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setbuf (3)
  • setbuf (3) ( Solaris man: Библиотечные вызовы )
  • >> setbuf (3) ( FreeBSD man: Библиотечные вызовы )
  • setbuf (3) ( Русские man: Библиотечные вызовы )
  • setbuf (3) ( Linux man: Библиотечные вызовы )
  • setbuf (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc


     - stream buffering operations


    Lb libc


       #include <stdio.h>
    void setbuf (FILE * restrict stream char * restrict buf);
    void setbuffer (FILE *stream char *buf int size);
    int setlinebuf (FILE *stream);
    int setvbuf (FILE * restrict stream char * restrict 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 ();
    function may be used to alter the buffering behavior of a stream. The Fa mode argument must be one of the following three macros:

    line buffered
    fully buffered

    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.)

    The setvbuf ();
    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 setvbuf (.);
    Except for the lack of a return value, 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);"


    The setvbuf ();
    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 ();
    function returns what the equivalent setvbuf ();
    would have returned.  


    fclose(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)  


    The setbuf ();
    and setvbuf ();
    functions conform to St -isoC .  


    The setbuffer ();
    and setlinebuf ();
    functions are not portable to versions of BSD before BSD 4.2 On BSD 4.2 and BSD 4.3 systems, setbuf ();
    always uses a suboptimal buffer size and should be avoided.




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