From: Joseph Myers Date: Fri, 6 Sep 2024 20:38:23 +0000 (+0000) Subject: Document limitations on streams passed to freopen X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=a2509a8bc955988f01f389a1cf74db3a9da42409;p=glibc.git Document limitations on streams passed to freopen As recently discussed, document that freopen does not work with streams opened with functions such as popen, fmemopen, open_memstream or fopencookie. I've filed to clarify this issue in POSIX. Tested with "make info" and "make html". --- diff --git a/manual/stdio.texi b/manual/stdio.texi index 29888a361f..8590ae955a 100644 --- a/manual/stdio.texi +++ b/manual/stdio.texi @@ -330,6 +330,14 @@ this ability, so using @code{freopen} is more portable. When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32 bit machine this function is in fact @code{freopen64} since the LFS interface replaces transparently the old interface. + +@Theglibc{} only supports use of @code{freopen} on streams opened with +@code{fopen} or @code{fopen64} and on the original values of the +standard streams @code{stdin}, @code{stdout}, and @code{stderr}; such +a stream may be reopened multiple times with @code{freopen}. If it is +called on another kind of stream (opened with functions such as +@code{popen}, @code{fmemopen}, @code{open_memstream}, and +@code{fopencookie}), @code{freopen} fails and returns a null pointer. @end deftypefun @deftypefun {FILE *} freopen64 (const char *@var{filename}, const char *@var{opentype}, FILE *@var{stream})