SETBUF(3) Linux Programmer's Manual SETBUF(3)
NAME
 setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations
SYNOPSIS
 #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:
 _DEFAULT_SOURCE
 Glibc 2.19 and earlier:
 _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. 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 buf-
 fer 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);
RETURN VALUE
 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.
ATTRIBUTES
 For an explanation of the terms used in this section, see at-
 tributes(7).
 +------------------------+---------------+---------+
 |Interface | Attribute | Value |
 +------------------------+---------------+---------+
 |setbuf(), setbuffer(), | Thread safety | MT-Safe |
 |setlinebuf(), setvbuf() | | |
 +------------------------+---------------+---------+
CONFORMING TO
 The setbuf() and setvbuf() functions conform to C89 and C99.
BUGS
 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;
 }
SEE ALSO
 stdbuf(1), fclose(3), fflush(3), fopen(3), fread(3), malloc(3),
 printf(3), puts(3)
COLOPHON
 This page is part of release 5.10 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
 https://www.kernel.org/doc/man-pages/.
Linux 2019年03月06日 SETBUF(3)