If the macro
was defined at the moment
was last included, the macro
generates no code, and hence does nothing at all.
Otherwise, the macro
prints an error message to standard error and terminates the program
is false (i.e., compares equal to zero).
The purpose of this macro is to help programmers find bugs in
The message "assertion failed in file foo.c, function
do_bar(), line 1287" is of no help at all to a user.
No value is returned.
For an explanation of the terms used in this section, see
POSIX.1-2001, POSIX.1-2008, C89, C99.
is required to be of type
and undefined behavior results if it is not, but in C99
it may have any scalar type.
is implemented as a macro; if the expression tested has side-effects,
program behavior will be different depending on whether
This may create Heisenbugs which go away when debugging
is turned on.
This page is part of release 4.04 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at