warning: incompatible implicit declaration of built-in function 'malloc'

[Ian Lance Taylor]

Robert Dell <dellr@mac.com> writes:

> can somebody please explain why I'm getting this warning?
> warning: incompatible implicit declaration of built-in function 'malloc'
>
> char *returnval = 0;
> long outputBytes = 0;
> ... outputBytes gets changed and tested to ensure it's valid (non zero) ...
>
> the offending line is here.
> returnval = (char *) malloc(outputBytes + 2);

You are calling the malloc function, but you have not declared it.  That
means it gets the type "extern int malloc();".  Since you are compiling
in hosted mode (the default), gcc knows that that declaration is
incorrect, and it is warning about that (the correct declaration is
"extern void *malloc(size_t);").

Typically this is fixed by adding

#include <stdlib.h>

to the start of your file.

Ian