1SETBUF(3)                  Linux Programmer's Manual                 SETBUF(3)
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NAME

6       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations
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SYNOPSIS

9       #include <stdio.h>
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11       void setbuf(FILE *stream, char *buf);
12       void setbuffer(FILE *stream, char *buf, size_t size);
13       void setlinebuf(FILE *stream);
14       int setvbuf(FILE *stream, char *buf, int mode , size_t size);
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DESCRIPTION

17       The  three types of buffering available are unbuffered, block buffered,
18       and line buffered.  When an output stream  is  unbuffered,  information
19       appears on the destination file or terminal as soon as written; when it
20       is block buffered many characters are saved up and written as a  block;
21       when  it  is  line  buffered characters are saved up until a newline is
22       output or input is read from any stream attached to a  terminal  device
23       (typically  stdin).   The  function  fflush(3) may be used to force the
24       block out early.   (See  fclose(3).)   Normally  all  files  are  block
25       buffered.   When the first I/O operation occurs on a file, malloc(3) is
26       called, and a buffer is obtained.  If a stream refers to a terminal (as
27       stdout  normally  does) it is line buffered.  The standard error stream
28       stderr is always unbuffered by default.
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30       The setvbuf() function may be used on any open  stream  to  change  its
31       buffer.  The mode parameter must be one of the following three macros:
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33              _IONBF unbuffered
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35              _IOLBF line buffered
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37              _IOFBF fully buffered
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39       Except  for unbuffered files, the buf argument should point to a buffer
40       at least size bytes long; this buffer will be used instead of the  cur‐
41       rent buffer.  If the argument buf is NULL, only the mode is affected; a
42       new buffer will be allocated on the next read or write operation.   The
43       setvbuf()  function  may only be used after opening a stream and before
44       any other operations have been performed on it.
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46       The other three calls are, in  effect,  simply  aliases  for  calls  to
47       setvbuf().  The setbuf() function is exactly equivalent to the call
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49              setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
50
51       The  setbuffer() function is the same, except that the size of the buf‐
52       fer is up to the caller, rather than being determined  by  the  default
53       BUFSIZ.  The setlinebuf() function is exactly equivalent to the call:
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55              setvbuf(stream, (char *)NULL, _IOLBF, 0);
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RETURN VALUE

58       The  function  setvbuf() returns 0 on success.  It can return any value
59       on failure, but returns non-zero when mode is invalid  or  the  request
60       cannot  be  honoured. It may set errno on failure.  The other functions
61       are void.
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CONFORMING TO

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

67       The setbuffer() and setlinebuf() functions are not portable to versions
68       of  BSD before 4.2BSD, and are available under Linux since libc 4.5.21.
69       On 4.2BSD and 4.3BSD systems, setbuf() always uses a suboptimal  buffer
70       size and should be avoided.
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72       You must make sure that both buf and the space it points to still exist
73       by the time stream is closed, which also happens  at  program  termina‐
74       tion.
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76       For example, the following is illegal:
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78       #include <stdio.h>
79       int main()
80       {
81           char buf[BUFSIZ];
82           setbuf(stdin, buf);
83           printf("Hello, world!\n");
84           return 0;
85       }
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87

SEE ALSO

89       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)
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93Linux                             2001-06-09                         SETBUF(3)
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