gnulib/doc/posix-functions/fopen.texi

@node fopen
@section @code{fopen}
@findex fopen

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html}

Gnulib module: fopen

Portability problems fixed by Gnulib:
@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 larger than 2 GB.  (Cf. @code{AC_SYS_LARGEFILE}.)
@item
On Windows platforms (excluding Cygwin), this function does usually not
recognize the @file{/dev/null} filename.
@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