You want GCC’s warn_unused_result
attribute:
#define WARN_UNUSED __attribute__((warn_unused_result))
int WARN_UNUSED f(int z) {
return z + (z*2) + z/3 + z*z + 23;
}
int main()
{
int i = 7;
f(i); ///// <<----- here i disregard the return value
return 1;
}
Trying to compile this code produces:
$ gcc test.c
test.c: In function `main':
test.c:16: warning: ignoring return value of `f', declared with
attribute warn_unused_result
You can see this in use in the Linux kernel; they have a __must_check
macro that does the same thing; looks like you need GCC 3.4 or greater for this to work. Then you will find that macro used in kernel header files:
unsigned long __must_check copy_to_user(void __user *to,
const void *from, unsigned long n);