промыть ручей (flush a stream)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
fflush — flush a stream
Синопсис (Synopsis)
#include <stdio.h>
int fflush(FILE *stream);
Описание (Description)
The functionality described on this reference page is aligned
with the ISO C standard. Any conflict between the requirements
described here and the ISO C standard is unintentional. This
volume of POSIX.1‐2017 defers to the ISO C standard.
If stream points to an output stream or an update stream in which
the most recent operation was not input, fflush() shall cause any
unwritten data for that stream to be written to the file, and the
last data modification and last file status change timestamps of
the underlying file shall be marked for update.
For a stream open for reading with an underlying file
description, if the file is not already at EOF, and the file is
one capable of seeking, the file offset of the underlying open
file description shall be set to the file position of the stream,
and any characters pushed back onto the stream by ungetc() or
ungetwc() that have not subsequently been read from the stream
shall be discarded (without further changing the file offset).
If stream is a null pointer, fflush() shall perform this flushing
action on all streams for which the behavior is defined above.
Возвращаемое значение (Return value)
Upon successful completion, fflush() shall return 0; otherwise,
it shall set the error indicator for the stream, return EOF, and
set errno to indicate the error.
Ошибки (Error)
The fflush() function shall fail if:
EAGAIN The O_NONBLOCK flag is set for the file descriptor
underlying stream and the thread would be delayed in the
write operation.
EBADF The file descriptor underlying stream is not valid.
EFBIG An attempt was made to write a file that exceeds the
maximum file size.
EFBIG An attempt was made to write a file that exceeds the file
size limit of the process.
EFBIG The file is a regular file and an attempt was made to
write at or beyond the offset maximum associated with the
corresponding stream.
EINTR The fflush() function was interrupted by a signal.
EIO The process is a member of a background process group
attempting to write to its controlling terminal, TOSTOP is
set, the calling thread is not blocking SIGTTOU, the
process is not ignoring SIGTTOU, and the process group of
the process is orphaned. This error may also be returned
under implementation-defined conditions.
ENOMEM The underlying stream was created by open_memstream() or
open_wmemstream() and insufficient memory is available.
ENOSPC There was no free space remaining on the device containing
the file or in the buffer used by the fmemopen() function.
EPIPE An attempt is made to write to a pipe or FIFO that is not
open for reading by any process. A SIGPIPE signal shall
also be sent to the thread.
The fflush() function may fail if:
ENXIO A request was made of a nonexistent device, or the request
was outside the capabilities of the device.
The following sections are informative.
Примеры (Examples)
Sending Prompts to Standard Output
The following example uses printf() calls to print a series of
prompts for information the user must enter from standard input.
The fflush() calls force the output to standard output. The
fflush() function is used because standard output is usually
buffered and the prompt may not immediately be printed on the
output or terminal. The getline() function calls read strings
from standard input and place the results in variables, for use
later in the program.
char *user;
char *oldpasswd;
char *newpasswd;
ssize_t llen;
size_t blen;
struct termios term;
tcflag_t saveflag;
printf("User name: ");
fflush(stdout);
blen = 0;
llen = getline(&user, &blen, stdin);
user[llen-1] = 0;
tcgetattr(fileno(stdin), &term);
saveflag = term.c_lflag;
term.c_lflag &= ~ECHO;
tcsetattr(fileno(stdin), TCSANOW, &term);
printf("Old password: ");
fflush(stdout);
blen = 0;
llen = getline(&oldpasswd, &blen, stdin);
oldpasswd[llen-1] = 0;
printf("\nNew password: ");
fflush(stdout);
blen = 0;
llen = getline(&newpasswd, &blen, stdin);
newpasswd[llen-1] = 0;
term.c_lflag = saveflag;
tcsetattr(fileno(stdin), TCSANOW, &term);
free(user);
free(oldpasswd);
free(newpasswd);
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
Data buffered by the system may make determining the validity of
the position of the current file descriptor impractical. Thus,
enforcing the repositioning of the file descriptor after fflush()
on streams open for read() is not mandated by POSIX.1‐2008.
Будущие направления (Future directions)
None.
Смотри также (See also)
Section 2.5, Standard I/O Streams, fmemopen(3p), getrlimit(3p),
open_memstream(3p), ulimit(3p)
The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)
