V10/man/adm/man3/setbuf.3

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.TH SETBUF 3S
.CT 2 file_io
.SH NAME
setbuf \(mi assign buffering to a stream
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.PP
.B setbuf(stream, buf)
.B FILE *stream;
.B char buf[BUFSIZ];
.fi
.SH DESCRIPTION
.I Setbuf
is used after a stream has been opened but before it
is read or written.
It causes the character array
.I buf
to be used instead of an automatically allocated buffer.
If
.I buf
is the constant pointer
.LR NULL ,
input/output will be completely unbuffered.
.PP
A buffer is normally obtained from
.IR  malloc (3)
upon the first
.IR getc (3)
or
.IR  putc
on the file.
Initially,
the standard stream
.I stderr
is unbuffered,
and the standard stream
.I stdout
is flushed automatically
whenever new data is read by
.IR getc .
The latter magic may be dissolved by a call to
.IR setbuf .
.SH "SEE ALSO"
.IR stdio (3), 
.IR malloc (3)