fflush() — Write Buffer to File

Format

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

Language Level: ANSI

Threadsafe: Yes.

Description

The fflush() function causes the system to empty the buffer that is associated with the specified output stream, if possible. If the stream is open for input, the fflush() function undoes the effect of any ungetc() function. The stream remains open after the call.

If stream is NULL, the system flushes all open streams.

Note:

The system automatically deletes buffers when you close the stream, or when a program ends normally without closing the stream.

Return Value

The fflush() function returns the value 0 if it successfully deletes the buffer. It returns EOF if an error occurs.

The value of errno can be set to:

Value: Meaning
ENOTOPEN: The file is not open.
ERECIO: The file is opened for record I/O.
ESTDIN: stdin cannot be opened.
EIOERROR: A non-recoverable I/O error occurred.
EIORECERR: A recoverable I/O error occurred.

The fflush() function is not supported for files that are opened with type=record.

Example that uses fflush()

This example deletes a stream buffer.

#include <stdio.h>
 
int main(void)
{
   FILE *stream;
   int ch;
   unsigned int result = 0;
 
   stream = fopen("mylib/myfile", "r");
   while ((ch = getc(stream)) != EOF && isdigit(ch))
      result = result * 10 + ch - '0';
   if (ch != EOF)
      ungetc(ch,stream);
 
   fflush(stream);           /* fflush undoes the effect of ungetc function
*/
   printf("The result is: %d\n", result);
   if ((ch = getc(stream)) != EOF)
      printf("The character is: %c\n", ch);
}

Related Information

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