setbuf(), setbuffer(), setlinebuf(), setvbuf() - stream buffering operations
#include <stdio.h>
void setbuf (FILE *stream, char *buf)
void setbuffer (FILE *stream, char *buf, size_t size)
void setlinebuf (FILE *stream)
int setvbuf (FILE *stream, char *buf, int mode, size_t size)
The three types of buffering available are unbuffered, block buffered, and line buffered. When an output stream is unbuffered, information appears on the destination file or terminal as soon as written; when it is block buffered many characters are saved up and written as a block; when it is line buffered characters are saved up until a newline is output or input is read from any stream attached to a terminal device (typically stdin). The function fflush(3) may be used to force the block out early. (See fclose(3).)
Normally all files are block buffered. When the first I/O operation occurs on a file, malloc(3) is called, and an optimally-sized buffer is obtained. If a stream refers to a terminal (as stdout normally does) it is line buffered. The standard error stream stderr is always unbuffered.
The setvbuf(3) function may be used to alter the buffering behavior of a stream. The mode parameter must be one of the following three macros:
In standard ANSI C implementations, the size parameter is the size of the buffer pointed to by buf. Normally, if buf is NULL, then size should be 0, and setvbuf(3) will allocate a buffer of size BUFSIZ. In this implementation, if buf is NULL but size is non-zero, setvbuf(3) (and setbuffer(3)) will allocate a buffer of size size and use that, releasing it on close. (Portable code should use a size of 0 with any NULL buffer.)
The size parameter may be given as zero to obtain deferred optimal-size buffer allocation as usual. If it is not zero, then except for unbuffered files, the buf argument should point to a buffer at least size bytes long; this buffer will be used instead of the current buffer.
The setvbuf(3) function may be used at any time, but may have peculiar side effects (such as discarding input or flushing output) if the stream is "active". Portable applications should call it only once on any given stream, and before any I/O is performed.
The other three calls are essentially aliases for calls to setvbuf(3). Except for the lack of a return value, the setbuf(3) function is exactly equivalent to the call
setvbuf(stream, buf, buf ? _IOFBF: _IONBF, BUFSIZ);
In the setbuffer(3) call, the size of the buffer is up to the caller, rather than being determined by the default BUFSIZE.
The setlinebuf(3) call is equivalent to the call:
setvbuf(stream, (char *)NULL, _IOLBF, 0);
The setvbuf(3) function returns 0 on success, or EOF if the request cannot be honored (note that the stream is still functional in this case).
The setlinebuf(3) function returns what the equivalent setvbuf(3) call would have returned.
fopen(3)
fclose(3)
fread(3)
malloc(3)
puts(3)
printf(3)