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setbuf
void setbuf ( FILE * stream , char * buffer ); | stdio.h |
| cplusplus.com |
Change stream buffering.
Changes the buffer used for I/O operations with the
specified stream, or, if the specified buffer is NULL
it disables buffering with the stream.
This function should be called once the file associated with the
stream has been opened
but before any input or output operation has been done.
The buffer must point to an array
BUFSIZ bytes long
(BUFSIZ is defined in stdio.h).
With buffered streams writing operations do not write directly to the
device associated with them; the data is accumulated in the buffer
and written to the device as a block. This can be forced flushing
the stream by calling
fflush or by closing the file
(fclose). All buffers are also flushed
when program terminates.
With unbuffered streams, data is directly written to the physical device on
each writing operation.
Normally, files are opened with a default allocated buffer, where this function can be used
to define a user-allocated buffer or to disable buffering for the file.
System standard streams like stdout and stderr are unbuffered by default
if they are not redirected.
Parameters.
Return Value.
none
Example.
/* setbuf example */
#include <stdio.h>
main()
{
char buffer[BUFSIZ];
FILE *pFile1, *pFile2;
pFile1=fopen ("myfile.txt","w");
pFile2=fopen ("myfile2.txt","a");
setbuf ( pFile1 , buffer );
fputs ("This is sent to a buffered stream",pFile1);
fflush (pFile1);
setbuff ( pFile2 , NULL );
fputs ("This is sent to an unbuffered stream",pFile2);
fclose (pFile1);
fclose (pFile2);
return 0;
}
Two files are opened with writing access. The stream associated with the file
example1.txt is set to a user allocated buffer; a writing operation to it is
done; the data is logically part of the stream now and a reading operation to it
can get this data, but it has not been phisically writen to the device (hard drive)
until the fflush has been called.
The second buffer in the example, associated with the file example2.txt, is
set to unbuffered, so the subsequent output operation is directly written to the device.
See also.
fopen,
fflush,
setvbuf