You can open an output stream that puts it data in an obstack. See section Obstacks.
Calling fflush
on this stream updates the current size of the
object to match the amount of data that has been written. After a call
to fflush
, you can examine the object temporarily.
You can move the file position of an obstack stream with fseek
or
fseeko
(see section File Positioning). Moving the file position past
the end of the data written fills the intervening space with zeros.
To make the object permanent, update the obstack with fflush
, and
then use obstack_finish
to finalize the object and get its address.
The following write to the stream starts a new object in the obstack,
and later writes add to that object until you do another fflush
and obstack_finish
.
But how do you find out how long the object is? You can get the length
in bytes by calling obstack_object_size
(see section Status of an Obstack), or you can null-terminate the object like this:
obstack_1grow (obstack, 0);
Whichever one you do, you must do it before calling
obstack_finish
. (You can do both if you wish.)
Here is a sample function that uses open_obstack_stream
:
char * make_message_string (const char *a, int b) { FILE *stream = open_obstack_stream (&message_obstack); output_task (stream); fprintf (stream, ": "); fprintf (stream, a, b); fprintf (stream, "\n"); fclose (stream); obstack_1grow (&message_obstack, 0); return obstack_finish (&message_obstack); }
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