NAME
assert —
expression verification
macro
SYNOPSIS
#include
<assert.h>
assert(expression);
DESCRIPTION
Theassert()
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);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);NDEBUG is defined, changing the semantics of the
program.
SEE ALSO
STANDARDS
The assert() macro conforms to
ISO/IEC 9899:1999
(“ISO C99”).
HISTORY
An assert macro appeared in
Version 7 AT&T UNIX.