assert(3) — Linux manual page


ASSERT(3)                 Linux Programmer's Manual                ASSERT(3)

NAME         top

       assert - abort the program if assertion is false

SYNOPSIS         top

       #include <assert.h>

       void assert(scalar expression);

DESCRIPTION         top

       This macro can help programmers find bugs in their programs, or
       handle exceptional cases via a crash that will produce limited
       debugging output.

       If expression is false (i.e., compares equal to zero), assert()
       prints an error message to standard error and terminates the program
       by calling abort(3).  The error message includes the name of the file
       and function containing the assert() call, the source code line
       number of the call, and the text of the argument; something like:

           prog: some_file.c:16: some_func: Assertion `val == 0' failed.

       If the macro NDEBUG is defined at the moment <assert.h> was last
       included, the macro assert() generates no code, and hence does noth‐
       ing at all.  It is not recommended to define NDEBUG if using assert()
       to detect error conditions since the software may behave non-deter‐

RETURN VALUE         top

       No value is returned.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value   │
       │assert()  │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, 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         top

       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.

SEE ALSO         top

       abort(3), assert_perror(3), exit(3)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                              2017-09-15                        ASSERT(3)

Pages that refer to this page: abort(3)assert_perror(3)