CODEWITHSUNDEEP
cfunctionpointers
zero cola
zero cola

Reputation: 99

function pointer assignments

Why am I able to assign a function that returns an int with no parameters specified to a function pointer that returns an int but takes an int argument?

For example when I do:

int f()
{ return 0;}

int (*ptr)(int) = f;

the compiler gives me no warnings

Upvotes: 2

Views: 311

Answers (2)

Kerrek SB
Kerrek SB

Reputation: 477512

In C, f doesn't take "no arguments", but rather "any arguments"*. Say int f(void) to declare "no arguments".

This is different from C++. Notably, C has separate notions of function "declaration" and function "prototype":

int f();              /* declaration -- f is still a mystery */
int f(int, double);   /* prototype -- now we know how to call f */
int f(int n, double c) { return -1; }  /* defintion -- now we can link */

*) As I said in the comment, "any arguments" is restricted to types that do not suffer default-promotion (in the same way as default-promotion happens to variadic arguments). That is, float, all flavours of char and of short int, and also ..., are not permissible in the actual function signature.

Upvotes: 5

kol
kol

Reputation: 28728

Which compiler do you use?

  • MinGW-GCC-3.4.2: invalid conversion fromint (*)()' to int (*)(int)'
  • Visual Studio 2010 Pro: Error 1 error C2440: 'initializing' : cannot convert from 'int (__cdecl *)(void)' to 'int (__cdecl *)(int)'

Upvotes: 0

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