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FreeBSD 11.0 - man page for assert (freebsd section 3)

ASSERT(3)						   BSD Library Functions Manual 						 ASSERT(3)

NAME
assert -- expression verification macro
SYNOPSIS
#include <assert.h> assert(expression);
DESCRIPTION
The assert() macro tests the given expression and if it is false, the calling process is terminated. A diagnostic message is written to stderr and the function abort(3) is called, effectively terminating the program. If expression is true, the assert() macro does nothing. The assert() macro may be removed at compile time by defining NDEBUG as a macro (e.g., by using the cc(1) option -DNDEBUG).
EXAMPLES
The assertion: assert(1 == 0); generates a diagnostic message similar to the following: Assertion failed: (1 == 0), function main, file assertion.c, line 100.
SEE ALSO
abort(3)
STANDARDS
The assert() macro conforms to ISO/IEC 9899:1999 (``ISO C99'').
HISTORY
An assert macro appeared in Version 6 AT&T UNIX.
BSD
January 26, 1999 BSD