Reference
C Library
IOstream Library
Strings library
STL Containers
STL Algorithms
Miscellaneous
C Library
cassert (assert.h)
cctype (ctype.h)
cerrno (errno.h)
cfloat (float.h)
ciso646 (iso646.h)
climits (limits.h)
clocale (locale.h)
cmath (math.h)
csetjmp (setjmp.h)
csignal (signal.h)
cstdarg (stdarg.h)
cstddef (stddef.h)
cstdio (stdio.h)
cstdlib (stdlib.h)
cstring (string.h)
ctime (time.h)
cstdio (stdio.h)
functions:
clearerr
fclose
feof
ferror
fflush
fgetc
fgetpos
fgets
fopen
fprintf
fputc
fputs
fread
freopen
fscanf
fseek
fsetpos
ftell
fwrite
getc
getchar
gets
perror
printf
putc
putchar
puts
remove
rename
rewind
scanf
setbuf
setvbuf
sprintf
sscanf
tmpfile
tmpnam
ungetc
vfprintf
vprintf
vsprintf
macro constants:
EOF
FILENAME_MAX
NULL
TMP_MAX
objects:
stderr
stdin
stdout
types:
FILE
fpos_t
size_t


fflush

function
<cstdio>
int fflush ( FILE * stream );

Flush stream

If the given stream was open for writing and the last i/o operation was an output operation, any unwritten data in the output buffer is written to the file.
If it was open for reading and the last operation was an input operation, the behavior depends on the specific library implementation. In some implementations this causes the input buffer to be cleared, but this is not standard behavior.
If the argument is a null pointer, all open files are flushed.
The stream remains open after this call.
When a file is closed, either because of a call to fclose or because the program terminates, all the buffers associated with it are automatically flushed.

Parameters

stream
Pointer to a FILE object that specifies a buffered stream.

Return Value

A zero value indicates success.
If an error occurs, EOF is returned and the error indicator is set (see feof).

Example

In files open for update (i.e., open for both reading and writting), the stream shall be flushed after an output operation before performing an input operation. This can be done either by repositioning (fseek, fsetpos, rewind) or by calling explicitly fflush, like in this example:

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/* fflush example */
#include <stdio.h>
char mybuffer[80];
int main()
{
   FILE * pFile;
   pFile = fopen ("example.txt","r+");
   if (pFile == NULL) perror ("Error opening file");
   else {
     fputs ("test",pFile);
     fflush (pFile);    // flushing or repositioning required
     fgets (mybuffer,80,pFile);
     puts (mybuffer);
     fclose (pFile);
     return 0;
  }
}


See also

fclose Close file (function)
fopen Open file (function)
setbuf Set stream buffer (function)
setvbuf Change stream buffering (function)