< c‎ | error
Defined in header <assert.h>
#ifdef NDEBUG

#define assert(condition) ((void)0)
#define assert(condition) /*implementation defined*/


The definition of the macro assert depends on another macro, NDEBUG, which is not defined by the standard library.

If NDEBUG is defined as a macro name at the point in the source code where <assert.h> is included, then assert does nothing.

If NDEBUG is not defined, then assert checks if its argument (which must have scalar type) compares equal to zero. If it does, assert outputs implementation-specific diagnostic information on the standard error output and calls abort(). The diagnostic information is required to include the text of expression, as well as the values of the standard macros __FILE__, __LINE__, and the standard variable __func__.


[edit] Parameters

condition - expression of scalar type

[edit] Return value


[edit] Example

#include <stdio.h>
// uncomment to disable assert()
// #define NDEBUG
#include <assert.h>
#include <math.h>
int main(void)
    double x = -1.0;
    assert(x >= 0.0);
    printf("sqrt(x) = %f\n", sqrt(x));   
    return 0;


output with NDEBUG not defined:
a.out: main.cpp:10: main: Assertion `x >= 0.0' failed.
output with NDEBUG defined:
sqrt(x) = -nan

[edit] See also

causes abnormal program termination (without cleaning up)
C++ documentation for assert