.\" Copyright (c) 1980, 1991 Regents of the University of California. .\" All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" the American National Standards Committee X3, on Information .\" Processing Systems. .\" .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" %%%LICENSE_END .\" .\" @(#)setbuf.3 6.10 (Berkeley) 6/29/91 .\" .\" Converted for Linux, Mon Nov 29 14:55:24 1993, faith@cs.unc.edu .\" Added section to BUGS, Sun Mar 12 22:28:33 MET 1995, .\" Thomas.Koenig@ciw.uni-karlsruhe.de .\" Correction, Sun, 11 Apr 1999 15:55:18, .\" Martin Vicente .\" Correction, 2000-03-03, Andreas Jaeger .\" Added return value for setvbuf, aeb, .\" .TH SETBUF 3 2019-03-06 "Linux" "Linux Programmer's Manual" .SH NAME setbuf, setbuffer, setlinebuf, setvbuf \- stream buffering operations .SH SYNOPSIS .nf .B #include .PP .BI "void setbuf(FILE *" stream ", char *" buf ); .PP .BI "void setbuffer(FILE *" stream ", char *" buf ", size_t " size ); .PP .BI "void setlinebuf(FILE *" stream ); .PP .BI "int setvbuf(FILE *" stream ", char *" buf ", int " mode \ ", size_t " size ); .fi .PP .in -4n Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .PP .BR setbuffer (), .BR setlinebuf (): Since glibc 2.19: _DEFAULT_SOURCE Glibc 2.19 and earlier: _BSD_SOURCE .SH 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 \fIstdin\fP). The function .BR fflush (3) may be used to force the block out early. (See .BR fclose (3).) .PP Normally all files are block buffered. If a stream refers to a terminal (as .I stdout normally does), it is line buffered. The standard error stream .I stderr is always unbuffered by default. .PP The .BR setvbuf () function may be used on any open stream to change its buffer. The .I mode argument must be one of the following three macros: .RS .TP .B _IONBF unbuffered .TP .B _IOLBF line buffered .TP .B _IOFBF fully buffered .RE .PP Except for unbuffered files, the .I buf argument should point to a buffer at least .I size bytes long; this buffer will be used instead of the current buffer. If the argument .I buf is NULL, only the mode is affected; a new buffer will be allocated on the next read or write operation. The .BR setvbuf () function may be used only after opening a stream and before any other operations have been performed on it. .PP The other three calls are, in effect, simply aliases for calls to .BR setvbuf (). The .BR setbuf () function is exactly equivalent to the call .PP .in +4n setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ); .in .PP The .BR setbuffer () function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default .BR BUFSIZ . The .BR setlinebuf () function is exactly equivalent to the call: .PP .in +4n setvbuf(stream, NULL, _IOLBF, 0); .in .SH RETURN VALUE The function .BR setvbuf () returns 0 on success. It returns nonzero on failure .RI ( mode is invalid or the request cannot be honored). It may set .I errno on failure. .PP The other functions do not return a value. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lbw23 lb lb l l l. Interface Attribute Value T{ .BR setbuf (), .BR setbuffer (), .br .BR setlinebuf (), .BR setvbuf () T} Thread safety MT-Safe .TE .SH CONFORMING TO The .BR setbuf () and .BR setvbuf () functions conform to C89 and C99. .SH BUGS .\" The .\" .BR setbuffer () .\" and .\" .BR 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, .\" .BR setbuf () .\" always uses a suboptimal buffer size and should be avoided. .PP You must make sure that the space that .I buf points to still exists by the time .I stream is closed, which also happens at program termination. For example, the following is invalid: .PP .EX #include int main(void) { char buf[BUFSIZ]; setbuf(stdin, buf); printf("Hello, world!\en"); return 0; } .EE .SH SEE ALSO .BR stdbuf (1), .BR fclose (3), .BR fflush (3), .BR fopen (3), .BR fread (3), .BR malloc (3), .BR printf (3), .BR puts (3) .SH COLOPHON This page is part of release 5.04 of the Linux .I 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/.