680 lines
20 KiB
Markdown
680 lines
20 KiB
Markdown
---
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title: Functions
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TARGET DECK: Obsidian::STEM
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FILE TAGS: c17::function
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tags:
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- c17
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---
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## Overview
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A function `f` without a following opening `(` is converted to a pointer to its start. This is called **function decay**.
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%%ANKI
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Basic
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What is the effect of function decay?
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Back: Evaluation of a function `f` without a following opening `(` is converted to a pointer to its start.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953243-->
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END%%
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%%ANKI
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Basic
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What name is given to the implicit conversion of a function to a pointer?
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Back: Function decay.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953247-->
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END%%
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%%ANKI
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Basic
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According to Gustedt, what C feature explains why are there no "function values"?
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Back: Function-to-pointer decay.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953250-->
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END%%
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%%ANKI
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Basic
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Why can't functions directly be made arguments to functions?
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Back: Because function arguments decay to pointers.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953255-->
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END%%
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%%ANKI
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Cloze
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{1:Function pointers} are to {2:`(...)`} whereas {2:pointers} are to {1:`[...]`}.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953260-->
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END%%
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%%ANKI
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Basic
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In what order are decays, dereferences, address ofs, and calls performed in the following?
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```c
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f(3);
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```
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Back: Decay, call.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953264-->
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END%%
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%%ANKI
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Basic
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In what order are decays, dereferences, address ofs, and calls performed in the following?
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```c
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(&f)(3);
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```
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Back: Address of, call.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953269-->
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END%%
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%%ANKI
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Basic
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In what order are decays, dereferences, address ofs, and calls performed in the following?
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```c
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(*f)(3);
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```
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Back: Decay, dereference, decay, call.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953273-->
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END%%
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%%ANKI
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Basic
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In what order are decays, dereferences, address ofs, and calls performed in the following?
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```c
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(*&f)(3);
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```
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Back: Address of, dereference, decay, call.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953277-->
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END%%
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%%ANKI
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Basic
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In what order are decays, dereferences, address ofs, and calls performed in the following?
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```c
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(&*f)(3);
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```
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Back: Decay, dereference, address of, call.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953281-->
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END%%
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%%ANKI
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Cloze
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{1:Pointers} refer to {2:arrays} whereas {2:function pointers} refer to {1:functions}.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732551953285-->
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END%%
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## Prototypes
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There exist two ways for a function [[c17/declarations|declaration]] to use declarators: **parameter type lists** and **identifier type lists**. To make the distinction clear, consider the following ways of defining an `add` function:
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```c
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int f(int x, int y) { return x + y; } // Paramter type list
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int f(x, y) int x; int y; { return x + y } // Identifier type list
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```
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A function **prototype** is a function declaration that specifies a function signature. There are three important points to make note of:
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* Empty identifier lists are interpreted as "the compiler has not been told what this function's arguments are."
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* The standard prohibits declaring functions with a non-empty identifier list.
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* Empty parameter lists are not allowed.
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Therefore:
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```c
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// Uses an empty identifer list. This declares a function `foo`
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// that takes an unknown specification of arguments.
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void foo();
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// Uses a non-empty identifier list. Compiler error.
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void foo(x, y);
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// Uses a non-empty identifier list. Compiler error.
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void foo(x, y) int x; int y;
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// Uses a non-empty identifier list. Definitions allow this.
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void foo(x, y) int x; int y; { }
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// Uses a non-empty parameter list. This prototypes a function
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// `foo` that takes no arguments.
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void foo(void);
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// Uses a non-empty parameter list. This prototypes and defines
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// a function `foo` that takes no arguments.
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void foo(void) {}
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```
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Together these points imply a function prototype *must* use a parameter type list.
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%%ANKI
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Basic
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Which of prototypes or declarations are more general?
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Back: Declarations.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751462-->
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END%%
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%%ANKI
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Basic
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What two ways are parameters declared in function declarations and definitions?
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Back: Identifier type lists and parameter type lists.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751467-->
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END%%
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%%ANKI
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Basic
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Which of identifier type lists and/or parameter type lists are considered obsolete?
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Back: Identifier type lists.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751470-->
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END%%
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%%ANKI
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Basic
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Define an addition function using identifier type lists.
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Back:
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```c
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int add(x, y) int x; int y; { return x + y; }
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```
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751473-->
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END%%
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%%ANKI
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Basic
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Define an addition function using parameter type lists.
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Back:
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```c
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int add(int x, int y) { return x + y; }
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```
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751476-->
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END%%
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%%ANKI
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Basic
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Is the following a prototype or a declaration?
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```c
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void foo();
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```
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Back: A declaration.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751479-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo();
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```
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Back: N/A.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751482-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo(x, y);
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```
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Back: A function declaration cannot have a non-empty identifier list.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751486-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo(x, y) int x; int y;
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```
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Back: A function declaration cannot have a non-empty identifier list.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751490-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo(x, y) int x; int y; {}
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```
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Back: N/A.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751495-->
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END%%
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%%ANKI
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Basic
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What function prototype is declared in the following?
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```c
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void foo(x, y) int x; int y; {}
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```
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Back: N/A. No prototype has been declared.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751499-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo();
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int main(void) { foo(1); }
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```
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Back: N/A.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751504-->
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END%%
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%%ANKI
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Basic
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Is the following a prototype, declaration, both, or neither?
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```c
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void f();
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```
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Back: A declaration.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1733492504375-->
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END%%
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%%ANKI
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Basic
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Is the following a prototype, declaration, both, or neither?
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```c
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void f(void);
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```
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Back: Both.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751509-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo(void);
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```
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Back: N/A.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751513-->
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END%%
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%%ANKI
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Basic
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What compilation error does the following raise?
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```c
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void foo(void);
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int main(void) { foo(1); }
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```
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Back: Too many arguments to function call `foo`.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751518-->
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END%%
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%%ANKI
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Basic
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What function prototype is declared in the following?
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```c
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void foo(int x, int y);
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```
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Back: `void foo(int, int)`
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751522-->
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END%%
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%%ANKI
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Basic
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What function prototype is declared in the following?
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```c
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void foo(int x, int y) {}
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```
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Back: `void foo(int, int)`
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751527-->
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END%%
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%%ANKI
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Basic
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How many arguments does the following declaration specify?
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```c
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void foo();
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```
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Back: Some number unknown to the compiler.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751531-->
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END%%
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%%ANKI
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Basic
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How many arguments does the following declaration specify?
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```c
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void foo(void);
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```
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Back: Zero.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751535-->
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END%%
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%%ANKI
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Basic
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Why might the following snippet raise a compilation error?
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```c
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int foo();
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int foo(int a);
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```
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Back: N/A. It likely wouldn't.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751539-->
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END%%
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%%ANKI
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Basic
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*Why* might the following snippet raise a compilation error?
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```c
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int foo();
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int foo(float a);
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```
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Back: Conflicting types. The first `foo` declares any `float` passed to it default promotes to a `double`.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751543-->
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END%%
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%%ANKI
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Basic
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*Why* might the following snippet raise a compilation error?
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```c
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int foo();
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int foo(char a);
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```
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Back: Conflicting types. The first `foo` declares any `char` passed to it default promotes to an `int`.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751547-->
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END%%
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%%ANKI
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Basic
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*Why* might the following snippet raise a compilation error?
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```c
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int foo();
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int foo(double a);
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```
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Back: N/A. It likely wouldn't.
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Reference: “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
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<!--ID: 1732031751552-->
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END%%
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### main
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`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:
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```c
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int main(void);
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int main(int argc, char* argv[argc+1]);
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```
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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`.
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%%ANKI
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Basic
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Which function serves as the entrypoint of C programs?
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Back: `main`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732293415792-->
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END%%
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%%ANKI
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Basic
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How many valid prototypes of `main` are available?
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Back: Indeterminate. Depends on the system.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732293415798-->
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END%%
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%%ANKI
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|
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%%
|
|
|
|
### Variable-Length Arrays
|
|
|
|
Within a function prototype, a parameter can denote a [[derived#Variable-Length|VLA]] using `[*]` syntax. For example, the following prototypes are all (more or less) equivalent:
|
|
|
|
```c
|
|
int sum2d(int , int , int a[*][*]);
|
|
int sum2d(int n, int , int a[n][*]);
|
|
int sum2d(int , int m, int a[*][m]);
|
|
int sum2d(int n, int m, int a[n][m]);
|
|
int sum2d(int , int , int a[][*]);
|
|
int sum2d(int , int , int (*a)[*]);
|
|
int sum2d(int , int m, int (*a)[m]);
|
|
```
|
|
|
|
%%ANKI
|
|
Basic
|
|
In what context are VLAs declared with `[*]` actually useful?
|
|
Back: Function prototypes.
|
|
Reference: https://stackoverflow.com/a/17371914
|
|
<!--ID: 1733144155068-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
Maintaining array syntax, rewrite the following without parameter names.
|
|
```c
|
|
int sum2d(int n, int m, int a[n][m]);
|
|
```
|
|
Back:
|
|
```c
|
|
int sum2d(int, int, int a[*][*]);
|
|
```
|
|
Reference: https://stackoverflow.com/a/17371914
|
|
<!--ID: 1733144155073-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
*Why* is the first `*` considered redundant in the following?
|
|
```c
|
|
int sum2d(int, int, int a[*][*]);
|
|
```
|
|
Back: Array decay.
|
|
Reference: https://stackoverflow.com/a/17371914
|
|
<!--ID: 1733144155076-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How can we rewrite the following with as few `*`s as possible?
|
|
```c
|
|
int sum2d(int, int, int a[*][*]);
|
|
```
|
|
Back:
|
|
```c
|
|
int sum2d(int, int, int a[][*]);
|
|
```
|
|
Reference: https://stackoverflow.com/a/17371914
|
|
<!--ID: 1733144155079-->
|
|
END%%
|
|
|
|
## Bibliography
|
|
|
|
* “ISO: Programming Languages - C17,” April 2017, [https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf](https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf).
|
|
* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020). |