Chapter 2. Diagnostics <assert.h>

The header <assert.h> defines the assert macro and refers to another macro.

NDEBUG

which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the point in the source file where <assert.h> is included, the assert macro is defined simply as

#define assert(ignore) ((void)0)

The assert macro is implemented as a macro, not as an actual function. If the macro definition is suppressed in order to access an actual function, the behavior is undefined.