C declarations were designed so that the **declaration** of an object looks like the use of the object. This isn't quite true - keywords like `volatile` and `const` only exist in declarations - but for the most part, this philosophy can be leveraged to read C declarations.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892098-->
END%%
## Declarations
A **declaration** consists of at least one type-specifier (e.g. `signed short`), storage class (e.g. `static`), and/or type qualifier (e.g. `const`) as well as one or more declarators.
%%ANKI
Basic
How many declarators does a declaration have?
Back: At least one.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892100-->
END%%
%%ANKI
Basic
How many declarations does a declarator have?
Back: N/A.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892101-->
END%%
%%ANKI
Basic
Which part of the following are declarators?
```c
int* a, b;
```
Back: `* a` and `b`.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892102-->
END%%
%%ANKI
Basic
Which part of the following are declarations?
```c
int* a, b;
```
Back: The entire line is a single declaration.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892103-->
END%%
%%ANKI
Basic
Which part of the following declaration is the declarator?
```c
const int *const x;
```
Back: `*const x`
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892104-->
END%%
%%ANKI
Basic
Which part of the following declaration is the type specifier?
```c
const int *const x;
```
Back: `int`
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892105-->
END%%
%%ANKI
Basic
Which part of the following declaration is the type qualifier?
```c
const int *const x;
```
Back: The first `const`.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892106-->
END%%
%%ANKI
Basic
What is the type of `x` in the following?
```c
const int *const x, y;
```
Back: `const int* const`
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892107-->
END%%
%%ANKI
Basic
What is the type of `y` in the following?
```c
const int *const x, y;
```
Back: `const int`
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892108-->
END%%
Declarations can be read by complying with the precedence rules outlined below:
1. Find the name of the declaration.
2. Obey the following precedence rules:
1. Parentheses grouping together parts of a declaration
2. Postfix operators `()` and `[]`
3. Prefix operator: the asterisk `*` denoting "pointer to"
3. If `const` and/or `volatile` keyword is next to a type specifier, it applies to the type specifier. Otherwise it applies to the pointer asterisk on its immediate left.
%%ANKI
Basic
In the precedence rules for C declarations, what available postfix operators are there?
Back: `()` and `[]`.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892113-->
END%%
%%ANKI
Basic
In the precedence rules for C declarations, what available prefix operators are there?
Back: Just `*`.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892114-->
END%%
%%ANKI
Basic
In the precedence rules for C declarations, what available type qualifiers are there?
Back: `const` and `volatile`.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892115-->
END%%
%%ANKI
Basic
What is the type of `foo` in the the following declaration?
```c
char *const *(*foo)();
```
Back: A pointer to a function returning a pointer to a `const` pointer-to-char.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892116-->
END%%
%%ANKI
Basic
What is the type of `foo` in the the following declaration?
```c
char *const *foo();
```
Back: A function returning a pointer to a `const` pointer-to-char.
Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
<!--ID: 1722786892117-->
END%%
%%ANKI
Basic
What is the type of `foo` in the the following declaration?
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?
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}`.
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
