@node fopen
@subsection @code{fopen}
@findex fopen

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/fopen.html}

Gnulib module: fopen or fopen-gnu
@mindex fopen
@mindex fopen-gnu

Portability problems fixed by either Gnulib module @code{fopen} or @code{fopen-gnu}:
@itemize
@item
This function does not fail when the file name argument ends in a slash
and (without the slash) names a nonexistent file or a file that is not a
directory, on some platforms:
HP-UX 11.00, AIX 7.1, Solaris 9.
@item
On platforms where @code{off_t} is a 32-bit type, @code{fopen} may not work
correctly with files 2 GiB and larger.  @xref{Large File Support}.
@item
On Windows platforms (excluding Cygwin), this function does usually not
recognize the @file{/dev/null} filename.
@end itemize

Portability problems fixed by Gnulib module @code{fopen-gnu}:
@itemize
@item
This function does not support the mode character
@samp{x} (corresponding to @code{O_EXCL}), introduced in ISO C11,
on some platforms:
FreeBSD 8.2, NetBSD 6.1, OpenBSD 5.6, Minix 3.2, AIX 6.1, HP-UX 11.31, Solaris 11.3, Cygwin 1.7.16 (2012), mingw with MSVCRT, MSVC 14.
@item
This function does not support the mode character
@samp{e} (corresponding to @code{O_CLOEXEC}),
introduced into a future POSIX revision through
@url{https://www.austingroupbugs.net/view.php?id=411}, on some platforms:
glibc 2.6, macOS 14, FreeBSD 9.0, NetBSD 5.1, OpenBSD 5.6, Minix 3.2, AIX 7.2, HP-UX 11.31, Solaris 11.3, Cygwin 1.7.16 (2012), mingw, MSVC 14.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
On Windows platforms (excluding Cygwin), this function does not set @code{errno}
upon failure.
@item
On Windows, this function returns a file stream in ``text'' mode by default;
this means that it translates @code{'\n'} to CR/LF by default.  Use the
@code{"b"} flag if you need reliable binary I/O.
@item
On Windows platforms (excluding Cygwin), this function fails to open
directories for reading.  Such streams have implementation-defined
semantics on other platforms.  To avoid directory streams with a
consistent error message, use @code{fstat} after @code{open} and
@code{fdopen}, rather than @code{fopen} and @code{fileno}.
@end itemize
