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+@node Function Portability
+@section Portability of Standard Functions
+@cindex functions
+
+Many standard library functions have portability limitations, although
+they are specified in the
+@uref{http://www.opengroup.org/susv3, Posix standard}.  In this section,
+we mention only functions that behave differently than specified; we don't
+mention functions that are not implemented at all on some platforms, or
+that are implemented but not declared on some platforms.  Many of the
+portability problems have a solution in @ref{Gnulib}.
+
+@table @code
+@item a64l
+This function was not correctly implemented in glibc versions before 2.2.5.
+
+@item accept
+Some systems don't have a @code{socklen_t} type; in this case this function's
+third argument type is @samp{int *}.
+
+@item asctime
+This function may overflow its internal buffer if an invalid year is passed.
+
+@item asctime_r
+This function may put more than 26 bytes into the argument buffer if an
+invalid year is passed.
+
+@item basename
+glibc has two different functions @code{basename}: the POSIX version and
+the GNU version.
+
+@code{basename} assumes file names in POSIX syntax; it does not with file
+names in Windows syntax.
+
+@item bcmp
+This function is marked as ``legacy'' in POSIX.  Better use @code{memcmp}
+instead.
+
+@item bcopy
+This function is marked as ``legacy'' in POSIX.  Better use @code{memcpy}
+or @code{memmove} instead.
+
+@item btowc
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item bzero
+This function is marked as ``legacy'' in POSIX.  Better use @code{memset}
+instead.
+
+@item chown
+When applied to a symbolic link, some implementations don't dereference
+the symlink, i.e. they behave like @code{lchown}.
+
+@item cproj
+@itemx cprojf
+@itemx cprojl
+The glibc implementation is or was broken.
+
+@item creat
+On Windows, this function returns a file handle in @code{O_TEXT} mode.  If you
+need a file handle in @code{O_BINARY} mode, you need to use the function
+@code{open} instead.
+
+On platforms where @code{off_t} is a 32-bit type, @code{creat} may not work
+correctly to create files larger than 2 GB.  The fix is to use the
+@code{AC_SYS_LARGEFILE} macro.
+
+@item ctime
+This function may overflow its internal buffer if an invalid year is passed.
+
+@item ctime_r
+This function may put more than 26 bytes into the argument buffer if an
+invalid year is passed.
+
+@item dirname
+@code{dirname} assumes file names in POSIX syntax; it does not with file
+names in Windows syntax.
+
+@item dlopen
+If the file name argument is not absolute, the file is searched for.  The
+search algorithm is system specific.
+
+@item dlsym
+The visibility of symbols loaded in dependent shared libraries or present
+in the main executable is system dependent.
+
+@item ecvt
+This function is marked as ``legacy'' in POSIX.  Better use @code{sprintf}
+instead.
+
+@item errno
+On Windows, the socket functions don't set @code{errno}; their error code is
+available through @code{WSAGetLastError()} instead.
+
+@item fclose
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item fcvt
+This function is marked as ``legacy'' in POSIX.  Better use @code{sprintf}
+instead.
+
+@item fdopen
+@itemx fflush
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+@item fgetc
+@itemx fgets
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+@item fgetwc
+@itemx fgetws
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item fnmatch
+This function is broken in some version of Solaris or glibc.
+
+@item fopen
+On Windows systems (excluding Cygwin), this function does not set @code{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.
+
+@item fork
+On some systems, @code{fork} followed by a call of the @code{exec} family
+(@code{execl}, @code{execlp}, @code{execle}, @code{execv}, @code{execvp},
+or @code{execve}) is less efficient than @code{vfork} followed by the same
+call.  @code{vfork} is a variant of @code{fork} that has been introduced to
+optimize the @code{fork}/@code{exec} pattern.
+
+On Windows systems (excluding Cygwin), this function is not implemented; use
+@code{spawnvp} instead.
+
+@item fprintf
+On NetBSD and Windows, this function doesn't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines this function so that it is
+POSIX compliant.
+
+On Windows, this function doesn't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item fputc
+@itemx fputs
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+@item fputwc
+@itemx fputws
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item fread
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item free
+On old systems, @code{free (NULL)} is not allowed.
+
+@item freopen
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item fscanf
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+On Windows, this function doesn't support the @code{hh}, @code{ll}, @code{j},
+@code{t}, @code{z} size specifiers.
+
+@item fseek
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item fstat
+On platforms where @code{off_t} is a 32-bit type, @code{stat} may not report
+correctly the size of files or block devices larger than 2 GB.  The fix is to
+use the @code{AC_SYS_LARGEFILE} macro.
+
+On Cygwin, @code{fstat} applied to the file descriptors 0 and 1, returns
+different @code{st_ino} values, even if standard input and standard output
+are not redirected and refer to the same terminal.
+
+@item ftime
+This function is marked as ``legacy'' in POSIX.  Better use @code{gettimeofday}
+or @code{clock_gettime} instead, and use @code{ftime} only as a fallback for
+portability to Windows systems.
+
+@item fwide
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@code{fwide} is not guaranteed to be able to change a file stream's mode
+to a different mode than the current one.
+
+@item fwprintf
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item fwrite
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item fwscanf
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item gcvt
+This function is marked as ``legacy'' in POSIX.  Better use @code{sprintf}
+instead.
+
+@item getaddrinfo
+On Windows, this function is declared in @code{<ws2tcpip.h>} rather than in
+@code{<netdb.h>}.
+
+@item getc
+@itemx getchar
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+@item getcwd
+On glibc systems, @code{getcwd (NULL, n)} allocates memory for the result.
+On other systems, this call is not allowed.
+
+@item getgroups
+On Ultrix 4.3, @code{getgroups (0, 0)} always fails.  See macro
+@samp{AC_FUNC_GETGROUPS}.
+
+@item gethostname
+If the given buffer is too small for the host name, some implementations
+fail with EINVAL, instead of returning a truncated host name.
+
+@item getopt
+The glibc implementation of @code{getopt} by default allows mixing option and
+non-option arguments on the command line in any order.  Other implementations,
+such as the one in Cygwin, enfore strict POSIX compliance: they require that
+the option arguments precede the non-option arguments.  This is something to
+watch out in your program's testsuite.
+
+@item getpeername
+Some systems don't have a @code{socklen_t} type; in this case this function's
+third argument type is @samp{int *}.
+
+@item getrusage
+Many systems don't fill in all the fields of @code{struct rusage} with
+meaningful values.
+
+@item gets
+This function should never be used, because it can overflow any given buffer.
+
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item getsockname
+Some systems don't have a @code{socklen_t} type; in this case this function's
+third argument type is @samp{int *}.
+
+@item getsockopt
+Some systems don't have a @code{socklen_t} type; in this case this function's
+fifth argument type is @samp{int *}.
+
+Many socket options are not available on all systems.
+
+BeOS has the @code{setsockopt} function, but not the @code{getsockopt}
+function.
+
+@item gettimeofday
+On some systems, @code{gettimeofday} clobbers the buffer in which
+@code{localtime} returns its result.
+
+@item getwc
+@itemx getwchar
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item getwd
+The size of the buffer required for this function is not a compile-time
+constant. Also, the function truncates a result that would be larger than
+the minimum buffer size. For these reasons, this function is marked as
+``legacy'' in POSIX.  Better use the @code{getcwd} function instead.
+
+@item glob
+Some systems may store additional flags in the @code{gl_flags} field.
+
+@item gmtime_r
+Some systems define a function of this name that is incompatible to POSIX.
+
+@item iconv
+This function was not correctly implemented in glibc versions before 2.2.
+
+When @code{iconv} encounters an input character that is valid but that can
+not be converted to the output character set, glibc's and GNU libiconv's
+@code{iconv} stop the conversion.  Some other implementations put an
+implementation-defined character in the output buffer.
+
+@item iconv_open
+The set of supported encodings and conversions is system dependent.
+
+@item index
+This function is marked as ``legacy'' in POSIX.  Better use @code{strchr}
+instead.
+
+@item inet_addr
+On some old systems, this function returns a @samp{struct in_addr} rather
+than a scalar type such as @samp{unsigned int} or @samp{unsigned long}.
+
+@item ioctl
+Most @code{ioctl} requests are platform and hardware specific.
+
+@item isatty
+On Windows, @code{isatty} also returns true for character devices such as
+"NUL".
+
+@item iswalnum
+@itemx iswalpha
+@itemx iswblank
+@itemx iswcntrl
+@itemx iswctype
+@itemx iswdigit
+@itemx iswgraph
+@itemx iswlower
+@itemx iswprint
+@itemx iswpunct
+@itemx iswspace
+@itemx iswupper
+@itemx iswxdigit
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item l64a
+This function was not correctly implemented in glibc versions before 2.2.5.
+
+@item localtime_r
+Some systems define a function of this name that is incompatible to POSIX.
+
+@item longjmp
+The effects of this call are system and compiler optimization dependent,
+since it restores the contents of register-allocated variables but not
+the contents of stack-allocated variables.
+
+When longjumping out of a signal handler that was being executed on an
+alternate stack (installed through @code{sigaltstack}), on FreeBSD, NetBSD,
+OpenBSD, you need to clear the @code{SS_ONSTACK} flag in the @code{stack_t}
+structure managed by the kernel.
+
+@item lseek
+POSIX does not specify which file descriptors support seeking and which don't.
+In practice, regular files and block devices support seeking, and ttys, pipes,
+and most character devices don't support it.
+
+On platforms where @code{off_t} is a 32-bit type, @code{lseek} does not work
+correctly with files larger than 2 GB.  The fix is to use the
+@code{AC_SYS_LARGEFILE} macro.
+
+@item lstat
+When the argument ends in a slash, some systems don't dereference the
+argument.
+
+On platforms where @code{off_t} is a 32-bit type, @code{lstat} may not report
+correctly the size of files or block devices larger than 2 GB.  The fix is to
+use the @code{AC_SYS_LARGEFILE} macro.
+
+@item mbrtowc
+@itemx mbsrtowcs
+@itemx mbstowcs
+@itemx mbtowc
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item mkdir
+When the argument ends in a slash, the function call fails on some systems.
+
+On Windows systems (excluding Cygwin), this function is called @code{_mkdir}
+and takes only one argument.  The fix is to define a macro like this:
+@smallexample
+#define mkdir ((int (*)()) _mkdir)
+@end smallexample
+
+@item mkstemp
+On some systems (HP-UX 10.20, SunOS 4.1.4, Solaris 2.5.1), mkstemp has a silly
+limit that it can create no more than 26 files from a given template.  On
+OSF/1 4.0f, it can create only 32 files per process.
+
+On systems other than glibc 2.0.7 or newer, @code{mkstemp} can create a
+world or group writable or readable file, if you haven't set the process'
+umask to 077.  This is a security risk.
+
+@item mktemp
+This function is not appropriate for creating temporary files.  (It has
+security risks.)  Therefore it is marked as ``legacy'' in POSIX.  Better use
+@code{mkstemp} instead.
+
+@item mktime
+Some implementations of @code{mktime} may go into an endless loop.
+
+@item mmap
+To get anonymous memory, on some systems, you can use the flags
+@code{MAP_ANONYMOUS | MAP_PRIVATE} and @code{-1} instead of a file descriptor;
+on others you have to use a read-only file descriptor of @file{/dev/zero}.
+
+On HP-UX, passing a non-NULL first argument, as a hint for the address (even
+without @code{MAP_FIXED}, often causes @code{mmap} to fail.  Better pass NULL
+in this case.
+
+On HP-UX, @code{MAP_FIXED} basically never works.  On other systems, it depends
+on the circumstances whether memory can be returned at a given address.
+
+@item mprotect
+On AIX, it is not possible to use @code{mprotect} on memory regions allocated
+with @code{malloc}.
+
+@item msync
+On NetBSD, @code{msync} takes only two arguments.
+
+@item nanosleep
+
+@item nice
+In glibc before glibc 2.2.4, @code{nice} returned 0 upon success.
+
+@item nl_langinfo
+Some older versions of glibc had @code{nl_langinfo} but not the @code{CODESET}
+macro.
+
+On Cygwin, which doesn't have locales, @code{nl_langinfo(CODESET)} always
+returns @code{"US-ASCII"}.
+
+@item open
+On Windows, this function returns a file handle in @code{O_TEXT} mode by
+default; this means that it translates '\n' to CR/LF by default.  Use the
+@code{O_BINARY} flag if you need reliable binary I/O.
+
+On platforms where @code{off_t} is a 32-bit type, @code{open} may not work
+correctly with files larger than 2 GB.  The fix is to use the
+@code{AC_SYS_LARGEFILE} macro.
+
+@item poll
+On MacOS X 10.4.0 and AIX 5.3, this function doesn't work on special files
+like @file{/dev/null} and ttys like @file{/dev/tty}.
+
+@item printf
+On NetBSD and Windows, this function doesn't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines this function so that it is
+POSIX compliant.
+
+On Windows, this function doesn't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item pthread_create
+On Linux/glibc systems before the advent of NPTL, signals could only be
+executed in one particular thread, not by any thread of the process.
+
+@item putc
+@itemx putchar
+@itemx puts
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+@item putwc
+@itemx putwchar
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item readlink
+When @code{readlink} is called on a directory: In the case of NFS mounted
+directories, Cygwin sets errno to ENOENT or EIO instead of EINVAL.  To avoid
+this problem, check for a directory before calling @code{readlink}.
+
+When @code{readlink} is called on a file that is not a symbolic link:
+Irix may set errno to ENXIO instead of EINVAL.  Cygwin may set errno to
+EACCES instead of EINVAL.
+
+@item realpath
+This function does not allow to determine the required size of output buffer;
+PATH_MAX - if it is defined - is nothing more than a guess.
+
+@item recvfrom
+Some systems don't have a @code{socklen_t} type; in this case this function's
+sixth argument type is @samp{int *}.
+
+@item regcomp
+@itemx regexec
+Many regular expression implementations have bugs.
+
+@item rename
+This function does not work on SunOS 4.1 when the source file name ends in a
+slash.
+
+@item rewind
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item rindex
+This function is marked as ``legacy'' in POSIX.  Better use @code{strrchr}
+instead.
+
+@item rmdir
+When @code{rmdir} fails because the specified directory is not empty, the
+@code{errno} value is system dependent.
+
+@item scanf
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+On Windows, this function doesn't support the @code{hh}, @code{ll}, @code{j},
+@code{t}, @code{z} size specifiers.
+
+@item select
+When you call @code{select} with a timeout, some implementations modify the
+timeout parameter so that upon return from the function, it contains the
+amount of time not slept.  Other implementations leave the timeout parameter
+unmodified.
+
+On Windows systems (excluding Cygwin) and on BeOS, @code{select} can only be
+called on descriptors created by the @code{socket} function, not on regular
+file descriptors.
+
+On Linux, when some file descriptor refers to a regular file, @code{select}
+may fail, setting errno to EBADF.
+
+@item setcontext
+The effects of this call are system and compiler optimization dependent,
+since it restores the contents of register-allocated variables but not
+the contents of stack-allocated variables.
+
+@item setenv
+In some versions of glibc (e.g. 2.3.3), @code{setenv} doesn't fail if the
+first argument contains a @samp{=} character.
+
+@item setjmp
+POSIX does not specify whether @code{setjmp} saves the signal mask in the
+@code{jmp_buf}.  It does on BSD systems, and on glibc systems when
+@code{_BSD_SOURCE} is defined; in this case @code{setjmp} behaves like
+@code{sigsetjmp}, and functions @code{_setjmp} and @code{_longjmp} are
+available that don't save or restore the signal mask.  On System V systems,
+and on glibc systems by default, @code{setjmp} doesn't save the signal mask.
+
+@item setlocale
+On Cygwin, which doesn't have locales, @code{setlocale(LC_ALL,NULL)} always
+returns @code{"C"}.
+
+@item setsockopt
+Many socket options are not available on all systems.
+
+@item setvbuf
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item shmat
+Attempts to @code{shmat} into a previously malloc-ed region fail on SunOS 4,
+with errno set to EINVAL, even if there is an @code{munmap} call in between.
+
+On Linux, the flag @code{SHM_REMAP} is needed in order to force @code{shmat}
+to replace existing memory mappings in the specify address range.  On other
+systems, it is not needed.
+
+@item shmget
+On many systems (not Linux), SHMMAX is so small that it is unusable for
+reasonable applications, and/or @code{shmget} requires superuser privileges.
+
+@item sigaction
+The symbolic value @code{SIG_IGN} for the @code{SIGCHLD} signal is equivalent
+to a signal handler
+@smallexample
+void handle_child (int sigchld)
+@{
+  while (waitpid (-1, NULL, WNOHANG) > 0)
+    ;
+@}
+@end smallexample
+except that @code{SIG_IGN} for @code{SIGCHLD} has the effect that the children
+execution times are not accounted in the @code{times} function.
+On some systems (BSD? SystemV? Linux?), you need to use the @code{sigaction}
+flag @code{SA_NOCLDWAIT} in order to obtain this behaviour.
+
+@item sigaltstack
+@code{sigaltstack} doesn't work on HP-UX 11/IA-64 and OpenBSD 3.6/Sparc64.
+
+@item signal
+On System V systems, when the signal is triggered, the kernel uninstalls the
+handler (i.e. resets the signal's action to SIG_DFL) before invoking the
+handler.  This opens the door to race conditions: undesired things happen
+if the signal is triggered twice and the signal handler was not quick enough
+reinstalling itself as a handler.  On BSD systems and glibc systems, on the
+other hand, when the signal is triggered, the kernel blocks the signal
+before invoking the handler.  This is saner, but POSIX still allows either
+behaviour.  To avoid this problem, use @code{sigaction} instead of
+@code{signal}.
+
+@item sigtimedwait
+Linux implements the meaning of NULL timeout by doing what @code{sigwaitinfo}
+does; other systems may not do the same.
+
+@item sigwait
+On Linux/glibc systems before the advent of NPTL, signals could only be
+executed in one particular thread, not by any thread of the process.
+
+@item sleep
+According to POSIX, the @code{sleep} function may interfere with the program's
+use of the @code{SIGALRM} signal.  On Linux, it doesn't; on other platforms,
+it may.
+
+@item snprintf
+On NetBSD and Windows, this function doesn't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines this function so that it is
+is POSIX compliant.
+
+On Windows, this function doesn't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item socket
+On BeOS, the descriptors returned by the @code{socket} function can not be used
+in calls to @code{read}, @code{write}, and @code{close}; you have to use
+@code{recv}, @code{send}, @code{closesocket} in these cases instead.
+
+@item sprintf
+On NetBSD and Windows, this function doesn't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines this function so that it is
+is POSIX compliant.
+
+On Windows, this function doesn't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item sscanf
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+On Windows, this function doesn't support the @code{hh}, @code{ll}, @code{j},
+@code{t}, @code{z} size specifiers.
+
+@item stat
+On platforms where @code{off_t} is a 32-bit type, @code{stat} may not report
+correctly the size of files or block devices larger than 2 GB.  The fix is to
+use the @code{AC_SYS_LARGEFILE} macro.
+
+Cygwin's @code{stat} function sometimes sets errno to EACCES when ENOENT would
+be more appropriate.
+
+@item strcasecmp
+@itemx strcasestr
+As of 2006, no system is known that implements these functions correctly in
+multibyte locales.
+
+@item strerror_r
+glibc has an incompatible version of this function.  The POSIX compliant code
+@smallexample
+char *s = (strerror_r (err, buf, buflen) == 0 ? buf : NULL);
+@end smallexample
+is essentially equivalent to this code using the glibc function:
+@smallexample
+char *s = strerror_r (err, buf, buflen);
+@end smallexample
+
+@item strstr
+As of 2006, no system is known that implements this function correctly in
+multibyte locales.
+
+@item swprintf
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+On Windows, this function does not take a buffer size as second argument.
+
+@item system
+On Windows systems (excluding Cygwin), the command processor used by the
+@code{system} function is @file{cmd.exe}, not @file{/bin/sh}.  Accordingly,
+the rules for quoting shell arguments containing spaces, quote or other special
+characters are different.
+
+@item tcdrain
+On some systems, @code{tcdrain} on a non-tty fails with errno set to EINVAL
+or, on MacOS X, also EOPNOTSUPP or ENODEV, rather than ENOTTY.
+
+@item tcflush
+On some systems, @code{tcflush} of @code{TCIFLUSH} on a non-tty fails with
+errno set to EINVAL rather than ENOTTY.
+
+On some systems, @code{tcflush} of @code{TCOFLUSH} on a non-tty fails with
+errno set to EINVAL or, on IRIX, also ENOSYS, or, on MacOS X, also EOPNOTSUPP
+or ENODEV, rather than ENOTTY.
+
+@item tempnam
+This function is not appropriate for creating temporary files.  (It has
+security risks.)  Better use @code{mkstemp} instead.
+
+@item tmpnam
+This function is not appropriate for creating temporary files.  (It has
+security risks.)  Better use @code{mkstemp} instead.
+
+@item towctrans
+@itemx towlower
+@itemx towupper
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item ungetc
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+@item ungetwc
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item unlink
+Removing an open file is unportable: On Unix this allows the programs that
+have the file already open to continue working with it; the file's storage
+is only freed when the no process has the file open any more.  On Windows,
+the attempt to remove an open file fails.
+
+@item usleep
+According to POSIX, the @code{usleep} function may interfere with the program's
+use of the @code{SIGALRM} signal.  On Linux, it doesn't; on other platforms,
+it may.
+
+@item utime
+On some systems, @code{utime (file, NULL)} fails to set the file's timestamp
+to the current time.
+
+@item utimes
+This function is marked as ``legacy'' in POSIX.  Better use @code{utime}
+instead.
+
+@item va_arg
+The second argument of @code{va_arg} must be a type that is invariant under
+the ``default argument promotions'' (ISO C 99 6.5.2.2 paragraph 6).  This
+means that the following are not valid here:
+@table @asis
+@item @samp{float}
+Use @samp{double} instead.
+@item @samp{bool}
+Use @samp{int} instead.
+@item Integer types smaller than @samp{int}.
+Use @samp{int} or @samp{unsigned int} instead.
+@end table
+
+This is a portability problem because you don't know the width of some
+abstract types like @code{uid_t}, @code{gid_t}, @code{mode_t}.  So, instead of
+@smallexample
+mode = va_arg (ap, mode_t);
+@end smallexample
+you have to write
+@smallexample
+mode = (sizeof (mode_t) < sizeof (int)
+        ? va_arg (ap, int)
+        : va_arg (ap, mode_t));
+@end smallexample
+
+@item va_copy
+Some platforms don't provide this macro.  You can use __va_copy where
+available instead, or otherwise an assignment or @code{memcpy} call.
+
+@item vfprintf
+On NetBSD and Windows, this function doesn't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines this function so that it is
+POSIX compliant.
+
+On Windows, this function doesn't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item vfscanf
+On Windows systems (excluding Cygwin), this function does not set @code{errno}
+upon failure.
+
+On Windows, this function doesn't support the @code{hh}, @code{ll}, @code{j},
+@code{t}, @code{z} size specifiers.
+
+@item vprintf
+@itemx vsnprintf
+@itemx vsprintf
+On NetBSD and Windows, these functions don't support format directives that
+access arguments in an arbitrary order, such as "%2$s".  The fix is to include
+@file{<libintl.h>} from GNU gettext; it redefines these functions so that they
+are POSIX compliant.
+
+On Windows, these functions don't support the @code{'} flag and the @code{hh},
+@code{ll}, @code{j}, @code{t}, @code{z} size specifiers.
+
+@item vscanf
+@item vsscanf
+On Windows systems (excluding Cygwin), these functions do not set @code{errno}
+upon failure.
+
+On Windows, these functions don't support the @code{hh}, @code{ll}, @code{j},
+@code{t}, @code{z} size specifiers.
+
+@item vswprintf
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+On Windows, this function does not take a buffer size as second argument.
+
+@item waitid
+As of 2005, no system is known on which @code{waitid} with flag @code{WNOWAIT}
+works correctly.
+
+@item wcrtomb
+@itemx wcscat
+@itemx wcschr
+@itemx wcscmp
+@itemx wcscoll
+@itemx wcscpy
+@itemx wcscspn
+@itemx wcsftime
+@itemx wcslen
+@itemx wcsncat
+@itemx wcsncmp
+@itemx wcsncpy
+@itemx wcspbrk
+@itemx wcsrchr
+@itemx wcsrtombs
+@itemx wcsspn
+@itemx wcsstr
+@itemx wcstod
+@itemx wcstof
+@itemx wcstoimax
+@itemx wcstok
+@itemx wcstol
+@itemx wcstold
+@itemx wcstoll
+@itemx wcstombs
+@itemx wcstoul
+@itemx wcstoull
+@itemx wcstoumax
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@item wcswcs
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+This function is marked as ``legacy'' in POSIX.  Better use @code{wcsstr}
+instead.
+
+@item wcswidth
+@itemx wcsxfrm
+@itemx wctob
+@itemx wctomb
+@itemx wctrans
+@itemx wctype
+@itemx wcwidth
+@itemx wmemchr
+@itemx wmemcmp
+@itemx wmemcpy
+@itemx wmemmove
+@itemx wmemset
+@itemx wprintf
+@itemx wscanf
+On Windows systems, @code{wchar_t} is a 16-bit type and therefore cannot
+accomodate all Unicode characters.
+
+@end table