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

NAME

     assert - abort the program if assertion is false

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  out-
     put.

     If  expression is false (i.e., compares equal to zero), assert() prints
     an error message to standard error and terminates the program by  call-
     ing  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-deterministi-
     cally.

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 |
     +----------+---------------+---------+

CONFORMING TO

     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

     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.