assert - abort the program if assertion is false
Standard C library (libc, -lc)
#include <assert.h>
void assert(scalar expression);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.
No value is returned.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
assert() |
Thread safety | MT-Safe |
C11, POSIX.1-2008.
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.
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.
abort(3), assert_perror(3), exit(3)