bsd man page for assert

ASSERT(3)						     Library Functions Manual							 ASSERT(3)

NAME
       assert - program verification

SYNOPSIS
       #include <assert.h>

       assert(expression)

DESCRIPTION
       Assert  is  a  macro that indicates expression is expected to be true at this point in the program.  It causes an exit(2) with a diagnostic
       comment on the standard output when expression is false (0).  Compiling with the cc(1) option -DNDEBUG effectively deletes assert from  the
       program.

DIAGNOSTICS
       `Assertion failed: file f line n.'  F is the source file and n the source line number of the assert statement.

7th Edition							   May 12, 1986 							 ASSERT(3)