ASSERT(3)              FreeBSD Library Functions Manual              ASSERT(3)

NAME
     assert - expression verification macro

SYNOPSIS
     #include <assert.h>

     assert(expression);

DESCRIPTION
     The assert() macro tests the given expression and if it is false, the
     calling process is terminated.  A diagnostic message is written to stderr
     and the function abort(3) is called, effectively terminating the program.

     If expression is true, the assert() macro does nothing.

     The assert() macro may be removed at compile time by defining NDEBUG as a
     macro (e.g., by using the cc(1) option -DNDEBUG).  Unlike most other
     include files, <assert.h> may be included multiple times.  Each time
     whether or not NDEBUG is defined determines the behavior of assert from
     that point forward until the end of the unit or another include of
     <assert.h>.

     The assert() macro should only be used for ensuring the developer's
     expectations hold true.  It is not appropriate for regular run-time error
     detection.

EXAMPLES
     The assertion:
           assert(1 == 0);
     generates a diagnostic message similar to the following:
           Assertion failed: (1 == 0), function main, file main.c, line 100.

     The following assert tries to assert there was no partial read:
           assert(read(fd, buf, nbytes) == nbytes);
     However, there are two problems.  First, it checks for normal conditions,
     rather than conditions that indicate a bug.  Second, the code will
     disappear if NDEBUG is defined, changing the semantics of the program.

SEE ALSO
     abort2(2), abort(3)

STANDARDS
     The assert() macro conforms to ISO/IEC 9899:1999 ("ISO C99").

HISTORY
     An assert macro appeared in Version 7 AT&T UNIX.

FreeBSD 13.1-RELEASE-p6          May 31, 2018          FreeBSD 13.1-RELEASE-p6