.TH MPU_SETVBUF 3 "August 2026" "libmpuio" "LIBMPUIO Programmer's Manual"
.SH NAME
mpu_setvbuf, mpu_setbuf, mpu_setlinebuf, mpu_feof, mpu_ferror, mpu_clearerr \- buffering and stream status
.SH SYNOPSIS
.nf
#include <libmpuio.h>

int       mpu_setvbuf( mpu_FILE *stream, unsigned char *buf,
                       int mode, size_t size );
void      mpu_setbuf( mpu_FILE *stream, unsigned char *buf );
void      mpu_setlinebuf( mpu_FILE *stream );
int       mpu_feof( mpu_FILE *stream );
int       mpu_ferror( mpu_FILE *stream );
void      mpu_clearerr( mpu_FILE *stream );
.fi
.SH DESCRIPTION
.B mpu_setvbuf
selects full buffering (MPU_IOFBF), line buffering (MPU_IOLBF), or no buffering
(MPU_IONBF).  A caller-supplied buffer is used directly until the stream is
closed or reconfigured.
.PP
.B mpu_setbuf
selects full buffering with MPU_BUFSIZ when buf is non-NULL and unbuffered mode
when buf is NULL.
.PP
.BR mpu_feof ,
.BR mpu_ferror ,
and
.B mpu_clearerr
inspect or clear stream status indicators.
.SH STATUS AND ERROR INDICATORS
.BR mpu_feof ()
reports the EOF indicator; it does not predict whether the next read will hit
EOF.  The indicator is set only after an input operation observes end of file.
.BR mpu_ferror ()
reports the stream error indicator.
.BR mpu_clearerr ()
clears both indicators.
.PP
EAGAIN/EWOULDBLOCK on a nonblocking descriptor sets error, not EOF.  After the
condition changes, clearerr followed by another input operation can continue.
.SH LOCKED AND UNLOCKED STATUS OPERATIONS
mpu_feof_unlocked, mpu_ferror_unlocked, and mpu_clearerr_unlocked have the same
indicator semantics but do not acquire the stream mutex.  Use them only with
exclusive stream access or while holding mpu_flockfile().
.PP
Buffer configuration functions have no unlocked variants.  Buffering should be
configured as a stream-state operation, not raced with active I/O.
.SH TRANSACTIONAL RECONFIGURATION
For descriptor and cookie streams, replacement storage is prepared before the
current buffer is synchronized or released.  If an internal buffer allocation
fails, mpu_setvbuf() returns an error while leaving the previous buffer,
active direction, and pending buffered data usable.  A later synchronization
failure may still change backend state as part of the attempted synchronization.

.SH SEE ALSO
.BR mpu_fopen (3),
.BR mpu_fflush (3),
.BR mpu_flushlbf (3),
.BR libmpuio (3)

.SH SETLINEBUF
.BR mpu_setlinebuf ()
is a glibc-style convenience interface equivalent to selecting
.B MPU_IOLBF
with an internally allocated buffer of
.B MPU_BUFSIZ
characters/bytes appropriate to the byte-buffer backend.  As with setbuf(3),
it has no return value; use mpu_setvbuf() when the caller needs explicit error
reporting.

.SH FLUSHING LINE-BUFFERED STREAMS
.BR mpu_flushlbf (3)
flushes all currently writing streams configured with MPU_IOLBF while leaving
fully buffered streams untouched.