|FFLUSH(3P)||POSIX Programmer's Manual||FFLUSH(3P)|
int fflush(FILE *stream);
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.
- The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the write operation.
- The file descriptor underlying stream is not valid.
- An attempt was made to write a file that exceeds the maximum file size.
- An attempt was made to write a file that exceeds the file size limit of the process.
- The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.
- The fflush() function was interrupted by a signal.
- 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.
- The underlying stream was created by open_memstream() or open_wmemstream() and insufficient memory is available.
- There was no free space remaining on the device containing the file or in the buffer used by the fmemopen() function.
- 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:
- A request was made of a nonexistent device, or the request was outside the capabilities of the device.
The following sections are informative.
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);
The Base Definitions volume of POSIX.1‐2017, <stdio.h>
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
|2017||IEEE/The Open Group|