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Intervals and reorganized C files.

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Joshua Potter 2024-11-27 07:43:44 -07:00
parent 4194fc6c47
commit c3ca1f107d
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notes/.obsidian/plugins/obsidian-to-anki-plugin/data.json
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@ -221,7 +221,8 @@
"arg-build-area.png",
"stack-frame.png",
"buffer-overflow.png",
"infinite-cartesian-product.png"
"infinite-cartesian-product.png",
"postage-function.png"
],
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"algebra/abs-val.md": "a47bc08db62304eb526d15ede3e300cf",
@ -959,7 +960,8 @@
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---
title: "2024-11-26"
title: "2024-11-27"
---
- [ ] Anki Flashcards

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@ -0,0 +1,11 @@
---
title: "2024-11-26"
---
- [x] Anki Flashcards
- [x] KoL
- [x] OGS
- [ ] Sheet Music (10 min.)
- [ ] Korean (Read 1 Story)
* Notes on [[intervals]].

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## Overview
For a large class of modern ISAs, storage for basic C datatypes respect **self-alignmnet**. This means `char`s can start on any byte address, `short`s on any even address, 4-byte `int`s and `float`s must start on an address divisible by 4, and `double`s must start on an address divisible by 8. Likewise pointers are also self-aligned.
For a large class of modern ISAs, storage for basic C datatypes respect **self-alignment**. This means `char`s can start on any byte address, `short`s on any even address, 4-byte `int`s and `float`s must start on an address divisible by 4, and `double`s must start on an address divisible by 8. Likewise pointers are also self-aligned.
Wasted space introduced solely for alignment purposes is referred to as **slop**.

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@ -275,497 +275,6 @@ Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Progra
<!--ID: 1722786892125-->
END%%
## Prototypes
A function declaration/definition has two ways of using declarators: **parameter type lists** and **identifier type lists**. To make the distinction clear, consider the following two ways of defining an `add` function:
```c
int f(int x, int y) { return x + y; } // Paramter type list
int f(x, y) int x; int y; { return x + y } // Identifier type list
```
A function **prototype** is a kind of function declaration that specifies the function signature. There are three important points to make note of:
* Empty identifier lists are interpreted as "the compiler has not been told what this function's arguments are."
* The standard prohibits declaring functions with a non-empty identifier list.
* Empty parameter lists are not allowed.
Therefore:
```c
// Uses an empty identifer list. This declares a function `foo`
// that takes an unknown specification of arguments.
void foo();
// Uses a non-empty identifier list. Compiler error.
void foo(x, y);
// Uses a non-empty identifier list. Compiler error.
void foo(x, y) int x; int y;
// Uses a non-empty identifier list. Definitions allow this.
void foo(x, y) int x; int y; { }
// Uses a non-empty parameter list. This prototypes a function
// `foo` that takes no arguments.
void foo(void);
// Uses a non-empty parameter list. This prototypes and defines
// a function `foo` that takes no arguments.
void foo(void) {}
```
Together these points imply a function prototype *must* use a parameter type list.
%%ANKI
Basic
Which of prototypes or declarations are more general?
Back: Declarations.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751462-->
END%%
%%ANKI
Basic
What two ways are parameters declared in function declarations and definitions?
Back: Identifier type lists and parameter type lists.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751467-->
END%%
%%ANKI
Basic
Which of identifier type lists and/or parameter type lists considered obsolete?
Back: Identifier type lists.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751470-->
END%%
%%ANKI
Basic
Define an addition function using identifier type lists.
Back:
```c
int add(x, y) int x; int y; { return x + y; }
```
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751473-->
END%%
%%ANKI
Basic
Define an addition function using parameter type lists.
Back:
```c
int add(int x, int y) { return x + y; }
```
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751476-->
END%%
%%ANKI
Basic
Is the following a prototype or a declaration?
```c
void foo();
```
Back: A declaration.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751479-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo();
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751482-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y);
```
Back: A function declaration cannot have a non-empty identifier list.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751486-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y) int x; int y;
```
Back: A function declaration cannot have a non-empty identifier list.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751490-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y) int x; int y; {}
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751495-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(x, y) int x; int y; {}
```
Back: N/A. No prototype has been declared.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751499-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo();
int main(void) { foo(1); }
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751504-->
END%%
%%ANKI
Basic
Is the following a prototype or a declaration?
```c
void f(void);
```
Back: A prototype.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751509-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(void);
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751513-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(void);
int main(void) { foo(1); }
```
Back: Too many arguments to function call `foo`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751518-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(int x, int y);
```
Back: `void foo(int, int)`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751522-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(int x, int y) {}
```
Back: `void foo(int, int)`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751527-->
END%%
%%ANKI
Basic
How many arguments does the following declaration specify?
```c
void foo();
```
Back: Some number unknown to the compiler.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751531-->
END%%
%%ANKI
Basic
How many arguments does the following declaration specify?
```c
void foo(void);
```
Back: Zero.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751535-->
END%%
%%ANKI
Basic
Why might the following snippet raise a compilation error?
```c
int foo();
int foo(int a);
```
Back: N/A. It likely wouldn't.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751539-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(float a);
```
Back: Conflicting types. The first `foo` declares any `float` passed to it default promotes to a `double`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751543-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(char a);
```
Back: Conflicting types. The first `foo` declares any `char` passed to it default promotes to an `int`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751547-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(double a);
```
Back: N/A. It likely wouldn't.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751552-->
END%%
### main
`main` is a special function serving as the entrypoint to C programs. It can have several different prototypes, but the following two are always possible:
```c
int main(void);
int main(int argc, char* argv[argc+1]);
```
The only two return values guaranteed to work on all platform is `EXIT_SUCCESS` and `EXIT_FAILURE`. Reaching the end of `main` is equivalent to a `reutrn` with value `EXIT_SUCCESS`.
%%ANKI
Basic
Which function serves as the entrypoint of C programs?
Back: `main`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415792-->
END%%
%%ANKI
Basic
How many valid prototypes of `main` are available?
Back: Indeterminate. Depends on the system.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415798-->
END%%
%%ANKI
Basic
How many "official" prototypes of `main` are available?
Back: Two.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415801-->
END%%
%%ANKI
Basic
What are the "official" prototypes of `main`?
Back:
```c
int main(void);
int main(int argc, char* argv[argc + 1]);
```
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415804-->
END%%
%%ANKI
Basic
What are the "official" prototypes of `main`?
Back:
```c
int main(void);
int main(int argc, char* argv[argc + 1]);
```
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
END%%
%%ANKI
Basic
What are the only portable values that `main` can return?
Back: `EXIT_SUCCESS` and `EXIT_FAILURE`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415807-->
END%%
%%ANKI
Basic
Which library defines `EXIT_SUCCESS`?
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415810-->
END%%
%%ANKI
Basic
Which library defines `EXIT_FAILURE`?
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415813-->
END%%
%%ANKI
Basic
What happens when `main` does not explicitly return a value?
Back: `EXIT_SUCCESS` is implicitly returned.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415816-->
END%%
%%ANKI
Cloze
Returning {1:`s`} in {1:`main`} is equivalent to invoking function {2:`exit`} with argument {2:`s`}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415819-->
END%%
%%ANKI
Basic
Which library declares the following prototype?
```c
noreturn void exit(int)
```
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415823-->
END%%
%%ANKI
Basic
What does keyword `_Noreturn` indicate?
Back: The associated callee will never return control back to the caller.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415827-->
END%%
%%ANKI
Basic
What kind of syntactical construct is `_Noreturn`?
Back: A special keyword.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415832-->
END%%
%%ANKI
Basic
What kind of syntactical construct is `noreturn`?
Back: A macro.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415836-->
END%%
%%ANKI
Cloze
{1:`_Noreturn`} is a {2:keyword} whereas {2:`noreturn`} is a {1:macro}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415841-->
END%%
%%ANKI
Basic
Which library is `noreturn` defined in?
Back: `stdnoreturn.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415846-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[0]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: The name of the program invocation.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415851-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[argc]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `0`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415856-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[1]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `0` if `argc == 1` else the first argument to the program.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415860-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the minimum value of `argc`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `1`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415865-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the minimum length of `argv`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `2`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415869-->
END%%
## Initializers
An **initializer** is an expression that gives an object a value at time of declaration. Only variable-length arrays (VLAs) do not allow for an initializer. The default initializer looks like `{0}`.

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@ -0,0 +1,608 @@
---
title: Functions
TARGET DECK: Obsidian::STEM
FILE TAGS: c17::function
tags:
- c17
---
## Overview
A function `f` without a following opening `(` is converted to a pointer to its start. This is called **function decay**.
%%ANKI
Basic
What is the effect of function decay?
Back: Evaluation of a function `f` without a following opening `(` is converted to a pointer to its start.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953243-->
END%%
%%ANKI
Basic
What name is given to the implicit conversion of a function to a pointer?
Back: Function decay.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953247-->
END%%
%%ANKI
Basic
According to Gustedt, what C feature explains why are there no "function values"?
Back: Function-to-pointer decay.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953250-->
END%%
%%ANKI
Basic
Why can't functions directly be made arguments to functions?
Back: Because function arguments decay to pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953255-->
END%%
%%ANKI
Cloze
{1:Function pointers} are to {2:`(...)`} whereas {2:pointers} are to {1:`[...]`}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953260-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
f(3);
```
Back: Decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953264-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(&f)(3);
```
Back: Address of, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953269-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(*f)(3);
```
Back: Decay, dereference, decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953273-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(*&f)(3);
```
Back: Address of, dereference, decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953277-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(&*f)(3);
```
Back: Decay, dereference, address of, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953281-->
END%%
%%ANKI
Cloze
{1:Pointers} refer to {2:arrays} whereas {2:function pointers} refer to {1:functions}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953285-->
END%%
## Prototypes
A function declaration/definition has two ways of using declarators: **parameter type lists** and **identifier type lists**. To make the distinction clear, consider the following two ways of defining an `add` function:
```c
int f(int x, int y) { return x + y; } // Paramter type list
int f(x, y) int x; int y; { return x + y } // Identifier type list
```
A function **prototype** is a kind of function [[c17/declarations|declaration]] that specifies the function signature. There are three important points to make note of:
* Empty identifier lists are interpreted as "the compiler has not been told what this function's arguments are."
* The standard prohibits declaring functions with a non-empty identifier list.
* Empty parameter lists are not allowed.
Therefore:
```c
// Uses an empty identifer list. This declares a function `foo`
// that takes an unknown specification of arguments.
void foo();
// Uses a non-empty identifier list. Compiler error.
void foo(x, y);
// Uses a non-empty identifier list. Compiler error.
void foo(x, y) int x; int y;
// Uses a non-empty identifier list. Definitions allow this.
void foo(x, y) int x; int y; { }
// Uses a non-empty parameter list. This prototypes a function
// `foo` that takes no arguments.
void foo(void);
// Uses a non-empty parameter list. This prototypes and defines
// a function `foo` that takes no arguments.
void foo(void) {}
```
Together these points imply a function prototype *must* use a parameter type list.
%%ANKI
Basic
Which of prototypes or declarations are more general?
Back: Declarations.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751462-->
END%%
%%ANKI
Basic
What two ways are parameters declared in function declarations and definitions?
Back: Identifier type lists and parameter type lists.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751467-->
END%%
%%ANKI
Basic
Which of identifier type lists and/or parameter type lists considered obsolete?
Back: Identifier type lists.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751470-->
END%%
%%ANKI
Basic
Define an addition function using identifier type lists.
Back:
```c
int add(x, y) int x; int y; { return x + y; }
```
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751473-->
END%%
%%ANKI
Basic
Define an addition function using parameter type lists.
Back:
```c
int add(int x, int y) { return x + y; }
```
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751476-->
END%%
%%ANKI
Basic
Is the following a prototype or a declaration?
```c
void foo();
```
Back: A declaration.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751479-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo();
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751482-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y);
```
Back: A function declaration cannot have a non-empty identifier list.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751486-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y) int x; int y;
```
Back: A function declaration cannot have a non-empty identifier list.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751490-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(x, y) int x; int y; {}
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751495-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(x, y) int x; int y; {}
```
Back: N/A. No prototype has been declared.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751499-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo();
int main(void) { foo(1); }
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751504-->
END%%
%%ANKI
Basic
Is the following a prototype or a declaration?
```c
void f(void);
```
Back: A prototype.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751509-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(void);
```
Back: N/A.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751513-->
END%%
%%ANKI
Basic
What compilation error does the following raise?
```c
void foo(void);
int main(void) { foo(1); }
```
Back: Too many arguments to function call `foo`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751518-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(int x, int y);
```
Back: `void foo(int, int)`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751522-->
END%%
%%ANKI
Basic
What function prototype is declared in the following?
```c
void foo(int x, int y) {}
```
Back: `void foo(int, int)`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751527-->
END%%
%%ANKI
Basic
How many arguments does the following declaration specify?
```c
void foo();
```
Back: Some number unknown to the compiler.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751531-->
END%%
%%ANKI
Basic
How many arguments does the following declaration specify?
```c
void foo(void);
```
Back: Zero.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751535-->
END%%
%%ANKI
Basic
Why might the following snippet raise a compilation error?
```c
int foo();
int foo(int a);
```
Back: N/A. It likely wouldn't.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751539-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(float a);
```
Back: Conflicting types. The first `foo` declares any `float` passed to it default promotes to a `double`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751543-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(char a);
```
Back: Conflicting types. The first `foo` declares any `char` passed to it default promotes to an `int`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751547-->
END%%
%%ANKI
Basic
*Why* might the following snippet raise a compilation error?
```c
int foo();
int foo(double a);
```
Back: N/A. It likely wouldn't.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1732031751552-->
END%%
### main
`main` is a special function serving as the entrypoint to C programs. It can have several different prototypes, but the following two are always possible:
```c
int main(void);
int main(int argc, char* argv[argc+1]);
```
The only two return values guaranteed to work on all platform is `EXIT_SUCCESS` and `EXIT_FAILURE`. Reaching the end of `main` is equivalent to a `reutrn` with value `EXIT_SUCCESS`.
%%ANKI
Basic
Which function serves as the entrypoint of C programs?
Back: `main`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415792-->
END%%
%%ANKI
Basic
How many valid prototypes of `main` are available?
Back: Indeterminate. Depends on the system.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415798-->
END%%
%%ANKI
Basic
How many "official" prototypes of `main` are available?
Back: Two.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415801-->
END%%
%%ANKI
Basic
What are the "official" prototypes of `main`?
Back:
```c
int main(void);
int main(int argc, char* argv[argc + 1]);
```
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415804-->
END%%
%%ANKI
Basic
What are the "official" prototypes of `main`?
Back:
```c
int main(void);
int main(int argc, char* argv[argc + 1]);
```
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
END%%
%%ANKI
Basic
What are the only portable values that `main` can return?
Back: `EXIT_SUCCESS` and `EXIT_FAILURE`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415807-->
END%%
%%ANKI
Basic
Which library defines `EXIT_SUCCESS`?
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415810-->
END%%
%%ANKI
Basic
Which library defines `EXIT_FAILURE`?
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415813-->
END%%
%%ANKI
Basic
What happens when `main` does not explicitly return a value?
Back: `EXIT_SUCCESS` is implicitly returned.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415816-->
END%%
%%ANKI
Cloze
Returning {1:`s`} in {1:`main`} is equivalent to invoking function {2:`exit`} with argument {2:`s`}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415819-->
END%%
%%ANKI
Basic
Which library declares the following prototype?
```c
noreturn void exit(int)
```
Back: `stdlib.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415823-->
END%%
%%ANKI
Basic
What does keyword `_Noreturn` indicate?
Back: The associated callee will never return control back to the caller.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415827-->
END%%
%%ANKI
Basic
What kind of syntactical construct is `_Noreturn`?
Back: A special keyword.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415832-->
END%%
%%ANKI
Basic
What kind of syntactical construct is `noreturn`?
Back: A macro.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415836-->
END%%
%%ANKI
Cloze
{1:`_Noreturn`} is a {2:keyword} whereas {2:`noreturn`} is a {1:macro}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415841-->
END%%
%%ANKI
Basic
Which library is `noreturn` defined in?
Back: `stdnoreturn.h`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415846-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[0]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: The name of the program invocation.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415851-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[argc]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `0`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415856-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the value of `argv[1]`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `0` if `argc == 1` else the first argument to the program.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415860-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the minimum value of `argc`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `1`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415865-->
END%%
%%ANKI
Basic
Consider the following prototype. What is the minimum length of `argv`?
```c
int main(int argc, char* argv[argc + 1]);
```
Back: `2`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732293415869-->
END%%
## Bibliography
* “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).

599
notes/c17/pointers.md Normal file
View File

@ -0,0 +1,599 @@
---
title: Pointers
TARGET DECK: Obsidian::STEM
FILE TAGS: c17::pointer
tags:
- c17
---
## Overview
Pointers have the same size as the machine's word size since it should be able to refer to any virtual address. All pointers are either **valid**, **null**, or **indeterminate**.
%%ANKI
Basic
*Why* does a pointer's size match the machine's word size?
Back: Because it should be able to refer to any virtual address.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1707493017246-->
END%%
%%ANKI
Basic
How is a pointer represented in binary?
Back: N/A. This is implementation specific.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551586-->
END%%
%%ANKI
Basic
What three states can a pointer be in?
Back: Valid, null, or indeterminate.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551590-->
END%%
%%ANKI
Basic
How is a pointer made null?
Back: By initializing or assigning the pointer to `0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551592-->
END%%
%%ANKI
Basic
When does a pointer evaluate to `false`?
Back: When it is a null pointer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551594-->
END%%
%%ANKI
Basic
When does a pointer evaluate to `true`?
Back: When it is not a null pointer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551596-->
END%%
%%ANKI
Basic
Suppose a pointer logically evaluates to `true`. Why might it still be unsafe to use?
Back: Logical evaluation can't distinguish valid pointers from indeterminate pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551598-->
END%%
%%ANKI
Basic
What is the result of dereferencing an indeterminate pointer?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551599-->
END%%
%%ANKI
Basic
What is the result of dereferencing a null pointer?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551601-->
END%%
%%ANKI
Basic
How is `r->field` equivalently written using `*`?
Back: `(*r).field`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730757470069-->
END%%
%%ANKI
Basic
How is `(*r).field` more compactly written?
Back: `r->field`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730757492874-->
END%%
%%ANKI
Basic
How many members *must* be defined in a `struct` initializer?
Back: One.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730758755505-->
END%%
%%ANKI
Basic
Are `struct`s passed by reference or value?
Back: Value.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730758755506-->
END%%
C allows arithmetic on pointers, where the computed value is scaled according to the size of the data type referenced by the pointer.
%%ANKI
Basic
How is the following (assumed valid) expression simplified?
```c
*&E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461664-->
END%%
%%ANKI
Basic
How is the following (assumed valid) expression simplified?
```c
&*E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461665-->
END%%
%%ANKI
Cloze
Pointer arithmetic {`*(A + i)`} is equivalent to array reference `A[i]`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461666-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[1][2];
}
```
Back: `return *(A + 6);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799783-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[2][0];
}
```
Back: `return *(A + 8);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799787-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][2];
}
```
Back: `return *(A + 5);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799789-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][0];
}
```
Back: `return *(A + 3);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799791-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return E; }
```
Back:
```asm
movq %rdi,%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461667-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E) { return E[0]; }
```
Back:
```asm
movl (%rdi),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461668-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E, int i) { return E[i]; }
```
Back:
```asm
movl (%rdi, %rsi, 4),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461669-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return &E[2]; }
```
Back:
```asm
leaq 8(%rdi),%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461670-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) p + 7
```
Back: `S + 28`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192201-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) (p + 7)
```
Back: `S + 7`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192210-->
END%%
%%ANKI
Basic
How do we declare a function pointer `fp` to the following?
```c
int foo(int x, int *p);
```
Back:
```c
int (*fp)(int, int *);
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192213-->
END%%
%%ANKI
Basic
What do the following two lines declare instances of?
```c
int (*fp)(int, int *);
int *fp(int, int *);
```
Back: The first is a function pointer. The second is a function.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192218-->
END%%
%%ANKI
Basic
What is the value of a function pointer?
Back: The address of the first instruction in the function's machine-code representation.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192229-->
END%%
%%ANKI
Basic
Trap representations are most relevant to what kind of derivied type?
Back: Pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726948-->
END%%
%%ANKI
Basic
What does a trap representation refer to?
Back: An invalid interpretation of a bit pattern as a specific type.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726951-->
END%%
%%ANKI
Basic
What happens when accessing an object with a trap representation of its type?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726952-->
END%%
%%ANKI
Basic
*Why* must a dereferenced object have the correct designated type?
Back: A trap representation of an object's type leads to undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726953-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 2;
```
Back: N/A. It is.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726954-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 3;
```
Back: Pointers cannot refer to addresses beyond that immediately following the array.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726955-->
END%%
%%ANKI
Basic
Refer to the following. What values of `N` yield a valid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `0`, `1`, and `2`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726956-->
END%%
%%ANKI
Basic
Refer to the following. What is the first value of `N` that yields an invalid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `3`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726957-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[1]);
```
Back: Yes.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726958-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[2]);
```
Back: No.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726959-->
END%%
%%ANKI
Cloze
A pointer must point to a {valid object}, or {one position beyond} a valid object, or be {null}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726960-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 2;
double q = *p;
```
Back: On the third line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726961-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 3;
double q = *p;
```
Back: On the second line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726962-->
END%%
## NULL
The `NULL` macro refers to a **null pointer constant**, an ICE with value `0` or such an expression cast to type `void*`. The following table lists some valid values `NULL` can take on:
| Expansion | Type |
| -------------------------- | -------------------- |
| `0U` | `unsigned` |
| `0` | `signed` |
| `\0` | `signed` |
| Enum constant of value `0` | `signed` |
| `0UL` | `unsigned long` |
| `0L` | `signed long` |
| `0ULL` | `unsigned long long` |
| `0LL` | `signed long long` |
| `(void*)0` | `void*` |
%%ANKI
Basic
How are null pointer constants defined in terms of ICEs?
Back: As any ICE with value `0` or such an expression cast to type `void*`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644395-->
END%%
%%ANKI
Basic
What *must* the `NULL` macro expand to?
Back: Any null pointer constant.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644434-->
END%%
%%ANKI
Basic
Which of the following members of the list are ICEs?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, and `0UL`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644440-->
END%%
%%ANKI
Basic
Which of the following members of the list are null pointer constants?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, `0UL`, and `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644446-->
END%%
%%ANKI
Basic
Which of the following members of the list could `NULL` be identical to?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, `0UL`, and `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644454-->
END%%
%%ANKI
Basic
Which of the following members of the list are pointer constants?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: Just `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644461-->
END%%
%%ANKI
Basic
Why does Gustedt discourage use of `NULL`?
Back: The type of value it expands to is implementation-specific.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644469-->
END%%
%%ANKI
Basic
What is wrong with the following invocation?
```c
printf("%d, %p", 1, NULL);
```
Back: `NULL` may not refer to a pointer type.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644475-->
END%%
%%ANKI
Basic
What value must `NULL` have for the following to be correct?
```c
printf("%d, %p", 1, NULL);
```
Back: `(void*)0`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644482-->
END%%
## Aliasing
Accessing the same object through different pointers is called **aliasing**. With the exclusion of [[simple#Character Types|character types]], only pointers of the same base type may alias.
%%ANKI
Basic
What does aliasing refer to?
Back: Accessing the same object through different pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646937-->
END%%
%%ANKI
Basic
Is aliasing possible in the following function?
```c
void foo(double const* a, double* b);
```
Back: Yes.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646945-->
END%%
%%ANKI
Basic
Is aliasing possible in the following function?
```c
void foo(double const* a, float* b);
```
Back: No.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646948-->
END%%
## Bibliography
* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).

689
notes/c17/types/derived.md
View File

@ -865,696 +865,11 @@ END%%
## Pointers
Pointers have the same size as the machine's word size since it should be able to refer to any virtual address. All pointers are either **valid**, **null**, or **indeterminate**.
%%ANKI
Basic
*Why* does a pointer's size match the machine's word size?
Back: Because it should be able to refer to any virtual address.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1707493017246-->
END%%
%%ANKI
Basic
How is a pointer represented in binary?
Back: N/A. This is implementation specific.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551586-->
END%%
%%ANKI
Basic
What three states can a pointer be in?
Back: Valid, null, or indeterminate.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551590-->
END%%
%%ANKI
Basic
How is a pointer made null?
Back: By initializing or assigning the pointer to `0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551592-->
END%%
%%ANKI
Basic
When does a pointer evaluate to `false`?
Back: When it is a null pointer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551594-->
END%%
%%ANKI
Basic
When does a pointer evaluate to `true`?
Back: When it is not a null pointer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551596-->
END%%
%%ANKI
Basic
Suppose a pointer logically evaluates to `true`. Why might it still be unsafe to use?
Back: Logical evaluation can't distinguish valid pointers from indeterminate pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551598-->
END%%
%%ANKI
Basic
What is the result of dereferencing an indeterminate pointer?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551599-->
END%%
%%ANKI
Basic
What is the result of dereferencing a null pointer?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730755551601-->
END%%
%%ANKI
Basic
How is `r->field` equivalently written using `*`?
Back: `(*r).field`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730757470069-->
END%%
%%ANKI
Basic
How is `(*r).field` more compactly written?
Back: `r->field`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730757492874-->
END%%
%%ANKI
Basic
How many members *must* be defined in a `struct` initializer?
Back: One.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730758755505-->
END%%
%%ANKI
Basic
Are `struct`s passed by reference or value?
Back: Value.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1730758755506-->
END%%
C allows arithmetic on pointers, where the computed value is scaled according to the size of the data type referenced by the pointer.
%%ANKI
Basic
How is the following (assumed valid) expression simplified?
```c
*&E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461664-->
END%%
%%ANKI
Basic
How is the following (assumed valid) expression simplified?
```c
&*E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461665-->
END%%
%%ANKI
Cloze
Pointer arithmetic {`*(A + i)`} is equivalent to array reference `A[i]`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461666-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[1][2];
}
```
Back: `return *(A + 6);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799783-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[2][0];
}
```
Back: `return *(A + 8);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799787-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][2];
}
```
Back: `return *(A + 5);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799789-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][0];
}
```
Back: `return *(A + 3);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799791-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return E; }
```
Back:
```asm
movq %rdi,%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461667-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E) { return E[0]; }
```
Back:
```asm
movl (%rdi),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461668-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E, int i) { return E[i]; }
```
Back:
```asm
movl (%rdi, %rsi, 4),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461669-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return &E[2]; }
```
Back:
```asm
leaq 8(%rdi),%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461670-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) p + 7
```
Back: `S + 28`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192201-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) (p + 7)
```
Back: `S + 7`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192210-->
END%%
%%ANKI
Basic
How do we declare a function pointer `fp` to the following?
```c
int foo(int x, int *p);
```
Back:
```c
int (*fp)(int, int *);
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192213-->
END%%
%%ANKI
Basic
What do the following two lines declare instances of?
```c
int (*fp)(int, int *);
int *fp(int, int *);
```
Back: The first is a function pointer. The second is a function.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192218-->
END%%
%%ANKI
Basic
What is the value of a function pointer?
Back: The address of the first instruction in the function's machine-code representation.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192229-->
END%%
%%ANKI
Basic
Trap representations are most relevant to what kind of derivied type?
Back: Pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726948-->
END%%
%%ANKI
Basic
What does a trap representation refer to?
Back: An invalid interpretation of a bit pattern as a specific type.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726951-->
END%%
%%ANKI
Basic
What happens when accessing an object with a trap representation of its type?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726952-->
END%%
%%ANKI
Basic
*Why* must a dereferenced object have the correct designated type?
Back: A trap representation of an object's type leads to undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726953-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 2;
```
Back: N/A. It is.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726954-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 3;
```
Back: Pointers cannot refer to addresses beyond that immediately following the array.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726955-->
END%%
%%ANKI
Basic
Refer to the following. What values of `N` yield a valid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `0`, `1`, and `2`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726956-->
END%%
%%ANKI
Basic
Refer to the following. What is the first value of `N` that yields an invalid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `3`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726957-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[1]);
```
Back: Yes.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726958-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[2]);
```
Back: No.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726959-->
END%%
%%ANKI
Cloze
A pointer must point to a {valid object}, or {one position beyond} a valid object, or be {null}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726960-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 2;
double q = *p;
```
Back: On the third line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726961-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 3;
double q = *p;
```
Back: On the second line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726962-->
END%%
### NULL
The `NULL` macro refers to a **null pointer constant**, an ICE with value `0` or such an expression cast to type `void*`. The following table lists some valid values `NULL` can take on:
| Expansion | Type |
| -------------------------- | -------------------- |
| `0U` | `unsigned` |
| `0` | `signed` |
| `\0` | `signed` |
| Enum constant of value `0` | `signed` |
| `0UL` | `unsigned long` |
| `0L` | `signed long` |
| `0ULL` | `unsigned long long` |
| `0LL` | `signed long long` |
| `(void*)0` | `void*` |
%%ANKI
Basic
How are null pointer constants defined in terms of ICEs?
Back: As any ICE with value `0` or such an expression cast to type `void*`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644395-->
END%%
%%ANKI
Basic
What *must* the `NULL` macro expand to?
Back: Any null pointer constant.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644434-->
END%%
%%ANKI
Basic
Which of the following members of the list are ICEs?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, and `0UL`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644440-->
END%%
%%ANKI
Basic
Which of the following members of the list are null pointer constants?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, `0UL`, and `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644446-->
END%%
%%ANKI
Basic
Which of the following members of the list could `NULL` be identical to?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: `0U`, `\0`, `0UL`, and `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644454-->
END%%
%%ANKI
Basic
Which of the following members of the list are pointer constants?
```c
0U, '\0', 0UL, (void*)0, 5LL
```
Back: Just `(void*)0`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644461-->
END%%
%%ANKI
Basic
Why does Gustedt discourage use of `NULL`?
Back: The type of value it expands to is implementation-specific.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644469-->
END%%
%%ANKI
Basic
What is wrong with the following invocation?
```c
printf("%d, %p", 1, NULL);
```
Back: `NULL` may not refer to a pointer type.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644475-->
END%%
%%ANKI
Basic
What value must `NULL` have for the following to be correct?
```c
printf("%d, %p", 1, NULL);
```
Back: `(void*)0`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732456644482-->
END%%
### Aliasing
Accessing the same object through different pointers is called **aliasing**. With the exclusion of [[simple#Character Types|character types]], only pointers of the same base type may alias.
%%ANKI
Basic
What does aliasing refer to?
Back: Accessing the same object through different pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646937-->
END%%
%%ANKI
Basic
Is aliasing possible in the following function?
```c
void foo(double const* a, double* b);
```
Back: Yes.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646945-->
END%%
%%ANKI
Basic
Is aliasing possible in the following function?
```c
void foo(double const* a, float* b);
```
Back: No.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732623646948-->
END%%
Pointers are another type of derived type. They are listed in more detail [[pointers|here]].
## Functions
A function `f` without a following opening `(` is converted to a pointer to its start. This is called **function decay**.
%%ANKI
Basic
What is the effect of function decay?
Back: Evaluation of a function `f` without a following opening `(` is converted to a pointer to its start.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953243-->
END%%
%%ANKI
Basic
What name is given to the implicit conversion of a function to a pointer?
Back: Function decay.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953247-->
END%%
%%ANKI
Basic
According to Gustedt, what C feature explains why are there no "function values"?
Back: Function-to-pointer decay.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953250-->
END%%
%%ANKI
Basic
Why can't functions directly be made arguments to functions?
Back: Because function arguments decay to pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953255-->
END%%
%%ANKI
Cloze
{1:Function pointers} are to {2:`(...)`} whereas {2:pointers} are to {1:`[...]`}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953260-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
f(3);
```
Back: Decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953264-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(&f)(3);
```
Back: Address of, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953269-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(*f)(3);
```
Back: Decay, dereference, decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953273-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(*&f)(3);
```
Back: Address of, dereference, decay, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953277-->
END%%
%%ANKI
Basic
In what order are decays, dereferences, address ofs, and calls performed in the following?
```c
(&*f)(3);
```
Back: Decay, dereference, address of, call.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953281-->
END%%
%%ANKI
Cloze
{1:Pointers} refer to {2:arrays} whereas {2:function pointers} refer to {1:functions}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732551953285-->
END%%
Functions are another type of derived type. They are listed in more detail [[c17/functions|here]].
## Bibliography

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---
title: Intervals
TARGET DECK: Obsidian::STEM
FILE TAGS: calculus::intervals
tags:
- calculus
---
## Overview
An interval corresponds to a continuous segment of the real number line. There are a few different types. For all $a, b \in \mathbb{R}$ satisfying $a < b$:
* $[a, b]$ denotes a **closed interval**, all $x$ satisfying $a \leq x \leq b$;
* $(a, b)$ denotes an **open interval**, all $x$ satisfying $a < x < b$;
* $(a, b]$ denotes a **half-open interval**, all $x$ satisfying $a < x \leq b$;
* $[a, b)$ denotes a half-open interval, all $x$ satisfying $a \leq x < b$.
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ and consider interval $[a, b]$. How is $a$ and $b$ assumed to relate?
Back: $a < b$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063663-->
END%%
%%ANKI
Cloze
Let $a, b \in \mathbb{R}$ s.t. $a < b$. Then {$[a, b]$} denotes a {closed} interval.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724929-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. How is $[a, b]$ expressed as a chain of inequalities?
Back: As all $x$ satisfying $a \leq x \leq b$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724934-->
END%%
%%ANKI
Cloze
Let $a, b \in \mathbb{R}$ s.t. $a < b$. Then {$(a, b)$} denotes an {open} interval.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724937-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. How is $(a, b)$ expressed as a chain of inequalities?
Back: As all $x$ satisfying $a < x < b$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724939-->
END%%
%%ANKI
Cloze
Let $a, b \in \mathbb{R}$ s.t. $a < b$. Then {$(a, b]$ and $[a, b)$]} denote {half-open} intervals.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724942-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. How is $(a, b]$ expressed as a chain of inequalities?
Back: As all $x$ satisfying $a < x \leq b$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724945-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. How is $[a, b)$ expressed as a chain of inequalities?
Back: As all $x$ satisfying $a \leq x < b$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724948-->
END%%
%%ANKI
Cloze
Interval {$(a, b)$} is called the {interior} of interval $[a, b]$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732624724952-->
END%%
## Partitions
Let $a, b \in \mathbb{R}$ such that $a < b$. A **partition** $P$ of interval $[a, b]$ is a set of points $x_0 = a, x_1, \ldots, x_{n-1}, x_n = b$ satisfying $$x_0 < x_1 < \cdots < x_{n-1} < x_n.$$
We use the symbol $P = \{x_0, x_1, \ldots, x_n\}$ to designate this partition.
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. What is a partition of interval $[a, b]$?
Back: A set of points $x_0 = a, x_1, \ldots, x_{n-1}, x_n = b$ satisfying $$x_0 < x_1 < \cdots < x_{n-1} < x_n.$$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063669-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$. How is a partition of interval $[a, b]$ denoted?
Back: As $\{a, x_1, \ldots, x_{n-1}, b\}$ where $a < x_1 < \cdots < x_{n-1} < b$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063671-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$ and $P = \{a, x_1, \ldots, x_{n-1}, b\}$ be a partition of $[a, b]$. What are $P$'s closed subintervals?
Back: $[a, x_1]$, $[x_1, x_2]$, $\ldots$, $[x_{n-1}, b]$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063674-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$ and $P = \{a, x_1, \ldots, x_{n-1}, b\}$ be a partition of $[a, b]$. What are $P$'s open subintervals?
Back: $(a, x_1)$, $(x_1, x_2)$, $\ldots$, $(x_{n-1}, b)$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063677-->
END%%
%%ANKI
Basic
Let $a, b \in \mathbb{R}$ s.t. $a < b$ and $P = \{a, x_1, \ldots, x_{n-1}, b\}$ be a partition of $[a, b]$. How are the members of $P$ assumed to relate?
Back: $a < x_1 < \cdots < x_{n-1} < b$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732626063679-->
END%%
A **refinement** $P'$ of some partition $P$ is created by adjoining more subdivision points to those of $P$. $P'$, also a partition, is said to be **finer** than $P$.
%%ANKI
Basic
Let $P$ be a partition of $[a, b]$. What is a refinement of $P$?
Back: A partition created by adjoining one or more subdivision points to those of $P$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945403-->
END%%
%%ANKI
Basic
Let $P'$ be a refinement on partition $P$ of $[a, b]$. How do $P$ and $P'$ relate?
Back: $P \subseteq P'$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945410-->
END%%
%%ANKI
Basic
Let $P'$ be a refinement on partition $P$ of $[a, b]$. Which of $P$ or $P'$ have more subdivision points?
Back: $P'$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945412-->
END%%
%%ANKI
Cloze
Let $P'$ be a refinement on partition $P$ of $[a, b]$. Then $P'$ is said to be {finer} than $P$.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945416-->
END%%
## Step Functions
A function $s$, whose domain is a closed interval $[a, b]$, is called a **step function** if and only if there exists a [[#Partitions|partition]] $P = \{a, x_1, \ldots, x_{n-1}, b\}$ of $[a, b]$ such that $s$ is constant on each open subinterval of $P$.
> At each of the endpoints $x_{k-1}$ and $x_k$, the function must have some well-defined value.
Step functions are also called **piecewise constant functions**.
%%ANKI
Basic
With maximum specificity, what is the domain of a step function?
Back: A closed interval.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945419-->
END%%
%%ANKI
Basic
Suppose $s$ is a step function with domain $[a, b]$. This implies existence of what?
Back: A partition of $[a, b]$ such that $s$ is constant on each open subinterval.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945421-->
END%%
%%ANKI
Basic
Let $s$ be a step function on $[a, b]$. What of its corresponding partition must be constant?
Back: The value along each open subinterval.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945430-->
END%%
%%ANKI
Basic
Let $s$ be a step function on $[a, b]$ with partition $P$. What criteria must the endpoints of $P$'s open subintervals satisfy?
Back: They must be well-defined.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945436-->
END%%
%%ANKI
Cloze
{Step} functions are also called {piecewise constant} functions.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945439-->
END%%
%%ANKI
Basic
The following is an example of what kind of function?
![[postage-function.png]]
Back: A step function.
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945442-->
END%%
%%ANKI
Basic
What minimally refined partition is associated with the following step function?
![[postage-function.png]]
Back: $\{0, 1, 2, 3, 4\}$
Reference: Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).
<!--ID: 1732627945444-->
END%%
## Bibliography
* Tom M. Apostol, _Calculus, Vol. 1: One-Variable Calculus, with an Introduction to Linear Algebra_, 2nd ed. (New York: Wiley, 1980).

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## Equinumerosity
We say set $A$ is **equinumerous** to set $B$, written ($A \approx B$) if and only if there exists a [[functions#Injections|one-to-one]] function from $A$ [[functions#Surjections|onto]] $B$.
We say set $A$ is **equinumerous** to set $B$, written ($A \approx B$) if and only if there exists a [[set/functions#Injections|one-to-one]] function from $A$ [[set/functions#Surjections|onto]] $B$.
%%ANKI
Basic