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SETBUF !!!SETBUF NAME SYNOPSIS DESCRIPTION RETURN VALUE CONFORMING TO BUGS SEE ALSO ---- !!NAME setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations !!SYNOPSIS __#include __ __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''__);__ !!DESCRIPTION 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 a 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 by default. The __setvbuf__ function may be used on any open stream to change its buffer. The ''mode'' parameter must be one of the following three macros: ___IONBF__ unbuffered ___IOLBF__ line buffered ___IOFBF__ fully buffered 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. If the argument ''buf'' is __NULL__, only the mode is affected; a new buffer will be allocated on the next read or write operation. The ''setvbuf'' function may only be used after opening a stream and before any other operations have been performed on it. The other three calls are, in effect, simply aliases for calls to __setvbuf__. The __setbuf__ function is exactly equivalent to the call setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ); The __setbuffer__ 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); !!RETURN VALUE The function __setvbuf__ returns 0 on success. It can return any value on failure, but returns nonzero when ''mode'' is invalid or the request cannot be honoured. It may set ''errno'' on failure. The other functions are void. !!CONFORMING TO The __setbuf__ and __setvbuf__ functions conform to ANSI X3.159-1989 (``ANSI C''). !!BUGS The __setbuffer__ and __setlinebuf__ functions are not portable to versions of BSD before 4.2BSD, and are available under Linux since libc 4.5.21. On 4.2BSD and 4.3BSD systems, __setbuf__ always uses a suboptimal buffer size and should be avoided. You must make sure that both ''buf'' and the space it points to still exist by the time ''stream'' is closed, which also happens at program termination. For example, the following is illegal: #include !!SEE ALSO fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3) ----
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