C in a Nutshell

Name

assert

Synopsis

Tests an expression

#include <assert.h>
voidassert( int expression );

The assert() macro evaluates a given expression and aborts the program if the result is 0 (that is, false). In this case, assert() also prints a message on stderr, indicating the name of the program, and the source file, line number, and function in which the failing assert() call occurs:

program: file:line: function: Assertion 'expression' failed.

If the value of expression is true (that is, nonzero), assert() does nothing and the program continues.

Use assert() during development to guard against logical errors in your program. When debugging is complete, you can instruct the preprocessor to suppress all assert() calls by defining the symbolic constant NDEBUG.

Example

int units_in_stock = 10;
int units_shipped = 9;
/* ... */
  units_shipped++;
  units_in_stock--;
/* ... */
  units_in_stock -= units_shipped;
  assert(units_in_stock >= 0);

This code produces the following output:

inventory: inventory.c:110: main: Assertion `units_in_stock >= 0' failed.
Aborted.

See Also

exit(), _Exit(), raise(), abort()