Next: siprintf, Previous: setlinebuf, Up: Stdio
setvbuf—specify file or stream buffering #include <stdio.h>
int setvbuf(FILE *fp, char *buf,
int mode, size_t size);
Description
Use setvbuf to specify what kind of buffering you want for the
file or stream identified by fp, by using one of the following
values (from stdio.h) as the mode argument:
_IONBF_IOFBF_IOLBFUse the size argument to specify how large a buffer you wish. You
can supply the buffer itself, if you wish, by passing a pointer to a
suitable area of memory as buf. Otherwise, you may pass NULL
as the buf argument, and setvbuf will allocate the buffer.
Warnings
You may only use setvbuf before performing any file operation other
than opening the file.
If you supply a non-null buf, you must ensure that the associated storage continues to be available until you close the stream identified by fp.
Returns
A 0 result indicates success, EOF failure (invalid mode or
size can cause failure).
Portability
Both ANSI C and the System V Interface Definition (Issue 2) require
setvbuf. However, they differ on the meaning of a NULL buffer
pointer: the SVID issue 2 specification says that a NULL buffer
pointer requests unbuffered output. For maximum portability, avoid
NULL buffer pointers.
Both specifications describe the result on failure only as a nonzero value.
Supporting OS subroutines required: close, fstat, isatty,
lseek, read, sbrk, write.