gnulib/doc/posix-headers/assert.texi

@node assert.h
@section @file{assert.h}

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/assert.h.html}

Gnulib module: assert-h

See also the Gnulib modules @code{assert} and @code{verify}.

Portability problems fixed by Gnulib:
@itemize
@item
On older platforms @code{static_assert} and @code{_Static_assert} do
not allow the second string-literal argument to be omitted.  For
example, GCC versions before 9.1 do not support the single-argument
@code{static_assert} that was standardized by C2X and C++17.
@item
Even-older platforms do not support @code{static_assert} or
@code{_Static_assert} at all.  For example, GCC versions before 4.6 do
not support @code{_Static_assert}, and G++ versions before 4.3 do not
support @code{static_assert}, which was standardized by C11 and C++11.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
C @code{_Static_assert} and C++ @code{static_assert}
are keywords that can be used without including @code{<assert.h>}.
The Gnulib substitutes are macros that require including @code{<assert.h>}.
@item
The C @code{static_assert} and @code{_Static_assert} can also
be used within a @code{struct} or @code{union} specifier, in place of
an ordinary declaration of a member of the struct or union.  The
Gnulib substitute can be used only as an ordinary declaration.
@item
In C99 and later, @code{assert} can be applied to any scalar expression.
In C89, the argument to @code{assert} is of type @code{int}.
@end itemize