fopen (GNU Gnulib)

Gnulib module: fopen or fopen-gnu

Portability problems fixed by either Gnulib module fopen or fopen-gnu:

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.
On platforms where off_t is a 32-bit type, fopen may not work correctly with files 2 GiB and larger. See Large File Support.
On Windows platforms (excluding Cygwin), this function does usually not recognize the /dev/null filename.

Portability problems fixed by Gnulib module fopen-gnu:

This function does not support the mode character ‘x’ (corresponding to 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, IRIX 6.5, Solaris 11.3, Cygwin 1.7.16 (2012), mingw, MSVC 14.
This function does not support the mode character ‘e’ (corresponding to O_CLOEXEC), introduced into a future POSIX revision through https://www.austingroupbugs.net/view.php?id=411, on some platforms: glibc 2.6, macOS 11.1, FreeBSD 9.0, NetBSD 5.1, OpenBSD 5.6, Minix 3.2, AIX 7.2, HP-UX 11.31, IRIX 6.5, Solaris 11.3, Cygwin 1.7.16 (2012), mingw, MSVC 14.

Portability problems not fixed by Gnulib:

On Windows platforms (excluding Cygwin), this function does not set errno upon failure.
On Windows, this function returns a file stream in “text” mode by default; this means that it translates '\n' to CR/LF by default. Use the "b" flag if you need reliable binary I/O.
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 fstat after open and fdopen, rather than fopen and fileno.