setbuf setbuffer setlinebuf setvbuf - stream buffering operations
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.
function may be used to alter the buffering behavior of a stream. The Fa mode argument must be one of the following three macros:
The Fa size argument 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 Fa buf argument should point to a buffer at least Fa size bytes long; this buffer will be used instead of the current buffer. If Fa buf is not NULL it is the caller's responsibility to free(3) this buffer after closing the stream. (If the Fa size argument is not zero but Fa buf is NULL a buffer of the given size will be allocated immediately, and released on close. This is an extension to ANSI C; portable code should use a size of 0 with any NULL buffer.)
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, in effect, simply aliases for calls to
Except for the lack of a return value, the setbuf ();
function is exactly equivalent to the call
"setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default BUFSIZ The setlinebuf ();
function is exactly equivalent to the call:
"setvbuf(stream, (char *)NULL, _IOLBF, 0);"
function returns what the equivalent setvbuf ();
would have returned.
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Created 1996-2022 by Maxim Chirkov
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