why sizeof(function_name) is 1

Question

Why is the result of:

sizeof(function_name)?

1? Somebody in community said that sizeof(main) is 1 but sizeof(main()) is 4. Here main is returning int, so it is returning 4. but if we do declaration as char main() instead of int main() it will return 1 only.

@MartinJames hmmm, `gcc` allows `main` to return char but gives a warning `clang` gives an error. I think I would prefer it to be an error. — Shafik Yaghmour, Feb 21 '14 at 14:27

score 3 · Answer 1 · edited Feb 21 '14 at 14:37

It's illegal to use sizeof on a function.

C99 §6.5.3.4 The sizeof operator

The sizeof operator shall not be applied to an expression that has function type or an incomplete type, to the parenthesized name of such a type, or to an expression that designates a bit-field member.

So if foo is the function name, sizeof(foo) is illegal, but sizeof(foo()) applies sizeof on the return value of foo(). main() returns int in standard C, it's 4 bytes on most machines today.

score 0 · Answer 2 · answered Feb 21 '14 at 14:22

0

sizeof(char) equals 1, always and everywhere.

So everything declared char would do also, and this already at compile-time.

answered Feb 21 '14 at 14:22

alk

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why sizeof(function_name) is 1

2 Answers2

C99 §6.5.3.4 The `sizeof` operator

why sizeof(function_name) is 1

2 Answers2

C99 §6.5.3.4 The sizeof operator

C99 §6.5.3.4 The `sizeof` operator