assert(3) -- Linux man page
NAMEassert - abort the program if assertion is false
#include <assert.h> void assert(scalar expression);
DESCRIPTIONIf the macro NDEBUG was defined at the moment <assert.h> was last included, the macro assert() generates no code, and hence does nothing at all. Otherwise, the macro assert() prints an error message to standard output and terminates the program by calling abort() if expression is false (i.e., compares equal to zero).
RETURN VALUENo value is returned.
CONFORMING TOISO9899 (ANSI C). In the 1990 standard, expression is required to be of type int and undefined behavior results if it is not, but in the 1999 standard it may have any scalar type.
BUGSassert() is implemented as a macro; if the expression tested has side-effects, program behaviour will be different depending on whether NDEBUG is defined. This may create Heisenbugs which go away when debugging is turned on.
SEE ALSOexit(3), abort(3), assert_perror(3)