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setbuf(3)
NAME
  setbuf, setvbuf, setvbuf_unlocked, setbuffer, setlinebuf - Assign buffering
  to a stream

LIBRARY
  Standard C Library (libc.so, libc.a)

SYNOPSIS
  #include <stdio.h>

  void setbuf(
	  FILE *stream,
	  char *buffer);

  int setvbuf(
	  FILE *stream,
	  char *buffer,
	  int mode,
	  size_t size);

  int setvbuf_unlocked(
	  FILE *stream,
	  char *buffer,
	  int mode,
	  size_t size);

  void setbuffer(
	  FILE *stream,
	  char *buffer,
	  int size);

  void setlinebuf(
	  FILE *stream);

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  setbuf(), setvbuf():	XPG4, XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  stream    Specifies the input/output stream.

  buffer    Points to a character array.

  mode	    Determines how the stream parameter is buffered.

  size	    Specifies the size of the buffer to be used.



DESCRIPTION
  The setbuf() function causes the character array pointed to by the buffer
  parameter to be used instead of an automatically allocated buffer.  Use the
  setbuf() function after a stream has been opened but before it is read or
  written.

  If the buffer parameter is a null pointer, input/output is unbuffered.

  A constant, BUFSIZ, defined in the stdio.h header file, tells how large an
  array is needed:

       char buf[BUFSIZ];

  For the setvbuf() function, the mode parameter determines how the stream
  parameter is buffered:

  _IOFBF    Causes input/output to be fully buffered.

  _IOLBF    Causes output to be line buffered.	The buffer is flushed when a
	    new line is written, the buffer is full, or input is requested.

  _IONBF    Causes input/output to be completely unbuffered.

  If the buffer parameter is not a null pointer, the array that the parameter
  points to is used for buffering instead of a buffer that is automatically
  allocated.  The size parameter specifies the size of the buffer to be used.
  The constant BUFSIZ in the stdio.h header file is one buffer size.  If
  input/output is unbuffered, the buffer and size parameters are ignored.

  The setbuffer() function, an alternate form of the setbuf() function, is
  used after stream has been opened but before it is read or written.  The
  character array buffer, whose size is determined by the size parameter, is
  used instead of an automatically allocated buffer. If the buffer parameter
  is a null pointer, input/output is completely unbuffered.

  The setbuffer() function is not needed under normal circumstances, since
  the default file I/O buffer size is optimal.

  The setlinebuf() function is used to change stdout or stderr from block
  buffered or unbuffered to line buffered.  Unlike the setbuf() and
  setbuffer() functions, the setlinebuf() function can be used any time the
  file descriptor is active.

  A buffer is normally obtained from the malloc() function at the time of the
  first getc() or putc() function on the file, except that the standard error
  stream, stderr, is normally not buffered.

  Output streams directed to terminals are always either line buffered or
  unbuffered.

  The setvbuf_unlocked() function is functionally identical to the setvbuf()
  function, except that setvbuf_unlocked() may be safely used only within a
  scope that is protected by the flockfile() and funlockfile() functions used
  as a pair.  The caller must ensure that the stream is locked before these
  functions are used.




RETURN VALUES
  The setvbuf() and setvbuf_unlocked() functions return zero when successful.
  If they cannot honor the request, or if you give an invalid value in the
  mode argument, they return a nonzero value.

NOTES
  A common source of error is allocating buffer space as an automatic
  variable in a code block, and then failing to close the stream in the same
  block.

ERRORS
  If the following condition occurs, the setvbuf() function sets errno to the
  corresponding value.

  [EBADF]   The file descriptor that underlies stream is invalid.

RELATED INFORMATION
  Functions: fopen(3), fread(3), getc(3), getwc(3), malloc(3), putc(3),
  putwc(3)

  Standards: standards(5)

Index for Section 3

Alphabetical listing for S

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