ASSERT

Section: Linux Programmer's Manual (3)
Updated: 2013-09-26
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NAME

assert - abort the program if assertion is false

SYNOPSIS

#include <assert.h>

void assert(scalar expression);

DESCRIPTION

If 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 error and terminates the program by calling abort(3) if expression is false (i.e., compares equal to zero).

The purpose of this macro is to help programmers find bugs in their programs. The message "assertion failed in file foo.c, function do_bar(), line 1287" is of no help at all to a user.

RETURN VALUE

No value is returned.

CONFORMING TO

POSIX.1-2001, C89, C99. In C89, expression is required to be of type int and undefined behavior results if it is not, but in C99 it may have any scalar type.

BUGS

assert() is implemented as a macro; if the expression tested has side-effects, program behavior will be different depending on whether NDEBUG is defined. This may create Heisenbugs which go away when debugging is turned on.

COLOPHON

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