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SETBUF(3) Linux Programmer's Manual SETBUF(3)


     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);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     setbuffer(), setlinebuf():
         Since glibc 2.19:
         Glibc 2.19 and earlier:


     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.  If a stream refers to a  termi-
     nal (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 argument 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  cur-
     rent 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 be used only 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, NULL, _IOLBF, 0);


     The  function  setvbuf()  returns  0 on success.  It returns nonzero on
     failure (mode is invalid or the request cannot be honored).  It may set
     errno on failure.
     The other functions do not return a value.


     For   an   explanation   of   the  terms  used  in  this  section,  see
     allbox; lbw23 lb lb l l l.  Interface Attribute Value T{ setbuf(), set-
     setlinebuf(), setvbuf() T}   Thread safety  MT-Safe


     The setbuf() and setvbuf() functions conform to C89 and C99.


     You  must  make  sure that the space that buf points to still exists by
     the time stream is closed, which also happens at  program  termination.
     For example, the following is invalid:
     #include <stdio.h>
     int main(void) {
         char buf[BUFSIZ];
         setbuf(stdin, buf);
         printf("Hello, world!\n");
         return 0; }


     stdbuf(1),   fclose(3),   fflush(3),   fopen(3),  fread(3),  malloc(3),
     printf(3), puts(3)


     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at

Linux 2017-09-15 SETBUF(3)

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