The <assert.h> header shall define the assert() macro. It
refers to the macro NDEBUG which is not defined in the header. If NDEBUG is
defined as a macro name before the inclusion of this header, the
assert() macro shall be defined simply as:
#define assert(ignore)((void) 0)
Otherwise, the macro behaves as described in assert().
The assert() macro shall be redefined according to the current state of
NDEBUG each time <assert.h> is included.
The assert() macro shall be implemented as a macro, not as a function. If
the macro definition is suppressed in order to access an actual function, the
behavior is undefined.
The following sections are informative.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html