assert(3) - Linux manual page (original) (raw)

assert(3) Library Functions Manual assert(3)

NAME top

   assert - abort the program if assertion is false

LIBRARY top

   Standard C library (_libc_, _-lc_)

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)](../man3/abort.3.html).  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 top

   No value is returned.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **assert**()                             │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   C11, POSIX.1-2008.

HISTORY top

   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 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)](../man3/abort.3.html), [assert_perror(3)](../man3/assert%5Fperror.3.html), [exit(3)](../man3/exit.3.html)

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Linux man-pages 6.10 2024-07-23 assert(3)

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