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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
   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

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.

SEE ALSO

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

COLOPHON

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.



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