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(Decoding Output): New node.

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Richard M. Stallman 2003-07-22 15:18:32 +00:00
parent 75442b3f43
commit 582ef186ea
1 changed files with 53 additions and 22 deletions
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75
lispref/processes.texi
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@ -898,29 +898,11 @@ you want to keep the output to those streams separate, you should
redirect one of them to a file--for example, by using an appropriate
shell command.
Subprocess output is normally decoded using a coding system before the
buffer or filter function receives it, much like text read from a file.
You can use @code{set-process-coding-system} to specify which coding
system to use (@pxref{Process Information}). Otherwise, the coding
system comes from @code{coding-system-for-read}, if that is
non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
Coding Systems}).
@strong{Warning:} Coding systems such as @code{undecided} which
determine the coding system from the data do not work entirely reliably
with asynchronous subprocess output. This is because Emacs has to
process asynchronous subprocess output in batches, as it arrives. Emacs
must try to detect the proper coding system from one batch at a time,
and this does not always work. Therefore, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion---that is, one like @code{latin-1-unix},
rather than @code{undecided} or @code{latin-1}.
@menu
* Process Buffers:: If no filter, output is put in a buffer.
* Filter Functions:: Filter functions accept output from the process.
* Accepting Output:: Explicitly permitting subprocess output.
Waiting for subprocess output.
* Process Buffers:: If no filter, output is put in a buffer.
* Filter Functions:: Filter functions accept output from the process.
* Decoding Ouptut:: Filters can get unibyte or multibyte strings.
* Accepting Output:: How to wait until process output arrives.
@end menu
@node Process Buffers
@ -1162,6 +1144,55 @@ there is no filter function:
@end smallexample
@end ignore
@node Decoding Output
@subsection Decoding Process Output
When Emacs writes process output directly into a multibyte buffer,
it decodes the output according to the process output coding system.
If the coding system is @code{raw-text} or @code{no-conversion}, Emacs
converts the unibyte output to multibyte using
@code{string-to-multibyte}, inserts the resulting multibyte text.
You can use @code{set-process-coding-system} to specify which coding
system to use (@pxref{Process Information}). Otherwise, the coding
system comes from @code{coding-system-for-read}, if that is
non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
Coding Systems}).
@strong{Warning:} Coding systems such as @code{undecided} which
determine the coding system from the data do not work entirely
reliably with asynchronous subprocess output. This is because Emacs
has to process asynchronous subprocess output in batches, as it
arrives. Emacs must try to detect the proper coding system from one
batch at a time, and this does not always work. Therefore, if at all
possible, specify a coding system that determines both the character
code conversion and the end of line conversion---that is, one like
@code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}.
@cindex filter multibyte flag, of process
@cindex process filter multibyte flag
When Emacs calls a process filter function, it provides the process
output as a multibyte string or as a unibyte string according to the
process's filter multibyte flag. If the flag is non-@code{nil}, Emacs
decodes the output according to the process output coding system to
produce a multibyte string, and passes that to the process. If the
flag is @code{nil}, Emacs puts the output into a unibyte string, with
no decoding, and passes that.
When you create a process, the filter multibyte flag takes its
initial value from @code{default-enable-multibyte-characters}. If you
want to change the flag later on, use
@code{set-process-filter-multibyte}.
@defun set-process-filter-multibyte process multibyte
This function sets the filter multibyte flag of @var{process}
to @var{multibyte}.
@end defun
@defun process-filter-multibyte-p process
This function returns the filter multibyte flag of @var{process}.
@end defun
@node Accepting Output
@subsection Accepting Output from Processes