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authorUlrich Drepper <drepper@redhat.com>2000-04-21 04:56:35 +0000
committerUlrich Drepper <drepper@redhat.com>2000-04-21 04:56:35 +0000
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treeb2b77a66479f301688a120ecd5dec0c6ba9f974c /manual/stdio.texi
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Update.
2000-03-08 H.J. Lu <hjl@gnu.org> * posix/regex.c (regex_compile): Correctly handle "\{" when the RE_INTERVALS is set and the RE_NO_BK_BRACES bit is not set.
Diffstat (limited to 'manual/stdio.texi')
-rw-r--r--manual/stdio.texi50
1 files changed, 40 insertions, 10 deletions
diff --git a/manual/stdio.texi b/manual/stdio.texi
index 4764003443..5c37698fc6 100644
--- a/manual/stdio.texi
+++ b/manual/stdio.texi
@@ -27,6 +27,7 @@ representing a communications channel to a file, device, or process.
@code{printf} and friends.
* Formatted Input:: @code{scanf} and related functions.
* EOF and Errors:: How you can tell if an I/O error happens.
+* Error Recovery:: What you can do about errors.
* Binary Streams:: Some systems distinguish between text files
and binary files.
* File Positioning:: About random-access streams.
@@ -3055,16 +3056,6 @@ value may be some other negative number.
@comment stdio.h
@comment ISO
-@deftypefun void clearerr (FILE *@var{stream})
-This function clears the end-of-file and error indicators for the
-stream @var{stream}.
-
-The file positioning functions (@pxref{File Positioning}) also clear the
-end-of-file indicator for the stream.
-@end deftypefun
-
-@comment stdio.h
-@comment ISO
@deftypefun int feof (FILE *@var{stream})
The @code{feof} function returns nonzero if and only if the end-of-file
indicator for the stream @var{stream} is set.
@@ -3088,6 +3079,45 @@ conditions defined for @code{write} are meaningful for these functions.
For more information about the descriptor-level I/O functions, see
@ref{Low-Level I/O}.
+@node Error Recovery
+@section Recovering from errors
+
+You may explicitly clear the error and EOF flags with the @code{clearerr}
+function.
+
+@comment stdio.h
+@comment ISO
+@deftypefun void clearerr (FILE *@var{stream})
+This function clears the end-of-file and error indicators for the
+stream @var{stream}.
+
+The file positioning functions (@pxref{File Positioning}) also clear the
+end-of-file indicator for the stream.
+@end deftypefun
+
+Note that it is @emph{not} correct to just clear the error flag and retry
+a failed stream operation. After a failed write, any number of
+characters since the last buffer flush may have been committed to the
+file, while some buffered data may have been discarded. Merely retrying
+can thus cause lost or repeated data.
+
+A failed read may leave the file pointer in an inappropriate position for
+a second try. In both cases, you should seek to a known position before
+retrying.
+
+Most errors that can happen are not recoverable --- a second try will
+always fail again in the same way. So usually it is best to give up and
+report the error to the user, rather than install complicated recovery
+logic.
+
+One important exception is @code{EINTR} (@pxref{Interrupted Primitives}).
+Many stream I/O implementations will treat it as an ordinary error, which
+can be quite inconvenient. You can avoid this hassle by installing all
+signals with the @code{SA_RESTART} flag.
+
+For similar reasons, setting nonblocking I/O on a stream's file
+descriptor is not usually advisable.
+
@node Binary Streams
@section Text and Binary Streams