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fflush()                  STDIO Function                 fflush()




Flush output stream's buffer

#include <stdio.h>
iinntt fffflluusshh(_f_p) FFIILLEE *_f_p;

fflush flushes any  buffered output data associated with the file
stream fp.   The file stream  stays open after  fflush is called.
fclose calls fflush, so there is  no need for you to call it when
normally closing a file or buffer.

***** Example *****

This  example demonstrates  fflush.  When run,  you will  see the
following:


        Line 1
        -----
        Line 1
        -----
        Line 1
        Line 2
        -----


The call


        fprintf(fp, "Line 2\n");


goes to a buffer and is  not in the file when file foo is listed.
However if you redirect the output  of this program to a file and
list the file, you will see:


        Line 1
        Line 1
        Line 1
        Line 2
        -----
        -----
        -----


because the line


        printf("-----\n");


goes into a  buffer and is not printed until  the program is over
and all buffers are flushed by exit().



COHERENT Lexicon                                           Page 1




fflush()                  STDIO Function                 fflush()



Although  the  COHERENT  screen  drivers  print  all  output  im-
mediately, not  all operating systems  work this way,  so when in
doubt, fflush().


#include <stdio.h>



main()
{
        FILE *fp;



        if (NULL == (fp = fopen("foo", "w")))
                exit(1);
        fprintf (fp, "Line 1\n");
        fflush (fp);
        system ("cat foo"); /* print Line 1 */



        printf("-----\n");
        fprintf(fp, "Line 2\n");
        system("cat foo"); /* print Line 1 */
        printf("-----\n");



        fflush(fp);
        system("cat foo"); /* print Line 1 Line 2 */
        printf("-----\n");
}


***** See Also *****

fclose(), setbuf(), STDIO, write()

***** Diagnostics *****

fflush returns  EOF if it cannot flush the  contents of the buff-
ers; otherwise it returns a meaningless value.

Note, also, that  all STDIO routines are buffered.  fflush should
be used to flush the output  buffer if you follow a STDIO routine
with an unbuffered routine.









COHERENT Lexicon                                           Page 2

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