1FFLUSH(3P)                 POSIX Programmer's Manual                FFLUSH(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       fflush - flush a stream
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SYNOPSIS

15       #include <stdio.h>
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17       int fflush(FILE *stream);
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DESCRIPTION

21       If stream points to an output stream or an update stream in  which  the
22       most recent operation was not input, fflush() shall cause any unwritten
23       data for that stream to be written to the file,  and the  st_ctime  and
24       st_mtime fields of the underlying file shall be marked for update.
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26       If  stream  is  a  null  pointer,  fflush() shall perform this flushing
27       action on all streams for which the behavior is defined above.
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RETURN VALUE

30       Upon successful completion, fflush()  shall  return  0;  otherwise,  it
31       shall  set  the  error  indicator  for the stream, return EOF,  and set
32       errno to indicate the error.
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ERRORS

35       The fflush() function shall fail if:
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37       EAGAIN The O_NONBLOCK flag is set for the  file  descriptor  underlying
38              stream and the process would be delayed in the write operation.
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40       EBADF  The file descriptor underlying stream is not valid.
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42       EFBIG  An  attempt  was  made  to write a file that exceeds the maximum
43              file size.
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45       EFBIG  An attempt was made to write a file that  exceeds  the  process'
46              file size limit.
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48       EFBIG  The  file  is a regular file and an attempt was made to write at
49              or beyond the offset maximum associated with  the  corresponding
50              stream.
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52       EINTR  The fflush() function was interrupted by a signal.
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54       EIO    The process is a member of a background process group attempting
55              to write to its controlling terminal, TOSTOP is set, the process
56              is  neither ignoring nor blocking SIGTTOU, and the process group
57              of the process is orphaned. This  error  may  also  be  returned
58              under implementation-defined conditions.
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60       ENOSPC There  was  no free space remaining on the device containing the
61              file.
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63       EPIPE  An attempt is made to write to a pipe or FIFO that is  not  open
64              for  reading by any process. A SIGPIPE signal shall also be sent
65              to the thread.
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68       The fflush() function may fail if:
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70       ENXIO  A request was made of a nonexistent device, or the  request  was
71              outside the capabilities of the device.
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74       The following sections are informative.
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EXAMPLES

77   Sending Prompts to Standard Output
78       The  following example uses printf() calls to print a series of prompts
79       for information the user must enter from standard input.  The  fflush()
80       calls  force  the  output  to standard output. The fflush() function is
81       used because standard output is usually buffered and the prompt may not
82       immediately be printed on the output or terminal. The gets() calls read
83       strings from standard input and place the results in variables, for use
84       later in the program.
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86
87              #include <stdio.h>
88              ...
89              char user[100];
90              char oldpasswd[100];
91              char newpasswd[100];
92              ...
93              printf("User name: ");
94              fflush(stdout);
95              gets(user);
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97
98              printf("Old password: ");
99              fflush(stdout);
100              gets(oldpasswd);
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102
103              printf("New password: ");
104              fflush(stdout);
105              gets(newpasswd);
106              ...
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APPLICATION USAGE

109       None.
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RATIONALE

112       Data  buffered  by  the system may make determining the validity of the
113       position of the current file descriptor  impractical.  Thus,  enforcing
114       the repositioning of the file descriptor after fflush() on streams open
115       for read() is not mandated by IEEE Std 1003.1-2001.
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FUTURE DIRECTIONS

118       None.
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SEE ALSO

121       getrlimit(),    ulimit(),    the    Base    Definitions    volume    of
122       IEEE Std 1003.1-2001, <stdio.h>
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125       Portions  of  this text are reprinted and reproduced in electronic form
126       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
127       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
128       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
129       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
130       event of any discrepancy between this version and the original IEEE and
131       The  Open Group Standard, the original IEEE and The Open Group Standard
132       is the referee document. The original Standard can be  obtained  online
133       at http://www.opengroup.org/unix/online.html .
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137IEEE/The Open Group                  2003                           FFLUSH(3P)
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