| .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) |
| .\" |
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| .\" Modified Sat Jul 24 21:42:42 1993 by Rik Faith <faith@cs.unc.edu> |
| .\" Modified Tue Oct 22 23:44:11 1996 by Eric S. Raymond <esr@thyrsus.com> |
| .\" Modified Thu Jun 2 23:44:11 2016 by Nikos Mavrogiannopoulos <nmav@redhat.com> |
| .TH ASSERT 3 2017-09-15 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| assert \- abort the program if assertion is false |
| .SH SYNOPSIS |
| .nf |
| .B #include <assert.h> |
| .PP |
| .BI "void assert(scalar " expression ); |
| .fi |
| .SH DESCRIPTION |
| This macro can help programmers find bugs in their programs, |
| or handle exceptional cases |
| via a crash that will produce limited debugging output. |
| .PP |
| If |
| .I expression |
| is false (i.e., compares equal to zero), |
| .BR assert () |
| prints an error message to standard error |
| and terminates the program by calling |
| .BR abort (3). |
| The error message includes the name of the file and function containing the |
| .BR assert () |
| call, the source code line number of the call, and the text of the argument; |
| something like: |
| .PP |
| prog: some_file.c:16: some_func: Assertion `val == 0' failed. |
| .PP |
| If the macro |
| .B NDEBUG |
| is defined at the moment |
| .I <assert.h> |
| was last included, the macro |
| .BR assert () |
| generates no code, and hence does nothing at all. |
| It is not recommended to define |
| .B NDEBUG |
| if using |
| .BR assert () |
| to detect error conditions since the software |
| may behave non-deterministically. |
| .SH RETURN VALUE |
| No value is returned. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lb lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR assert () |
| T} Thread safety MT-Safe |
| .TE |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008, C89, C99. |
| In C89, |
| .I expression |
| is required to be of type |
| .I int |
| and undefined behavior results if it is not, but in C99 |
| it may have any scalar type. |
| .\" See Defect Report 107 for more details. |
| .SH BUGS |
| .BR assert () |
| is implemented as a macro; if the expression tested has side-effects, |
| program behavior will be different depending on whether |
| .B NDEBUG |
| is defined. |
| This may create Heisenbugs which go away when debugging |
| is turned on. |
| .SH SEE ALSO |
| .BR abort (3), |
| .BR assert_perror (3), |
| .BR exit (3) |