Page History

...

Suppose the custom <myassert.h> declares a function assert() that does nonstandard verification, and the standard <assert.h> defines an assert macro as required by the standard.

#include <myassert.h>
#include <assert.h>

void fullAssert(int e) {
  assert(0 < e); // invoke standard library assert()
  (assert)(0 < e);   // assert() macro suppressed, calling function assert()
}

...

The programmer should place nonstandard verification in a function that does not conflict with the standard library macro assert, for example, myassert().

#include <myassert.h>
#include <assert.h>

void fullAssert(int e) {
  assert(0 < e); // standard library assert()
  myassert(e); // well defined custom assertion function
}

...

Legacy code is apt to include an incorrect declaration, such as the following.

extern int errno;

Compliant Solution (Redefining errno)

The correct way to declare errno is to include the header <errno.h>.

#include <errno.h>

Implementations conforming to C99 are required to declare errno in <errno.h>, although some historic implementations failed to do so.

...