assert(3) — Linux manual page

assert(3)               Library Functions Manual               assert(3)

NAME

       assert - abort the program if assertion is false

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <assert.h>

       void assert(scalar expression);

DESCRIPTION

       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
       nothing at all.  It is not recommended to define NDEBUG if using
       assert() to detect error conditions since the software may behave
       non-deterministically.

RETURN VALUE

       No value is returned.

ATTRIBUTES

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌─────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                           │ Attribute     │ Value   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │ assert()                            │ Thread safety │ MT-Safe │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C89, C99, POSIX.1-2001.

       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.

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                      assert(3)

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

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