How to hack Gnu api

  When it comes to Gnu, many linux learner will ask me how to hack Gnu api? Okay, today i will communicate with you to introduce my way to hack it.
  Assuming we want to know how to use setbuf function following is the steps.

1, man setbuf | more -integer.
2, get the codes.
3, study it.

This is my study code.

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



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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setbuffer(), setlinebuf(): _BSD_SOURCE

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 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 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 returns non-zero 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.

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

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 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

       int
       main(void)
       {
           char buf[BUFSIZ];
           setbuf(stdin, buf);
           printf("Hello, world!\n");
           return 0;
       }

SEE ALSO
       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

COLOPHON
       This  page  is  part of release 3.15 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at



Linux                             2008-06-26                         SETBUF(3)


Reference: man manual.