Fflush

fflush is a C function belonging to the ANSI C standard library, and included in the file stdio.h. Its purpose is to write any buffered output data for the specified stream.

Function prototype

:int fflush(FILE "*stream_pointer");

Argument meaning:
* "stream_pointer" is either a pointer to the output stream for which the buffered data is to be written, or "NULL". If "NULL" is passed as an argument fflush flushes all opened output streams.

Return value

The return value is an "integer" which means:
* "0" (zero) : function performed successfully in the stream.
* "EOF" : an error occurred and errno is set.

Note that each error number has a distinct meaning. The meaning can usually be revealed by checking "errno.h"; the strerror() function converts an error number to a descriptive text string.

Remarks

* The "fflush" function is usually used to prevent data loss by ensuring that the data is written to stream
* It should be used for output streams only; otherwise the behavior is undefined.
* Often "fflush" is used on the standard output stream because stdout is usually buffered and the output might not be prompted immediately.
* A call to fclose will flush the stream.
* A null argument did not have defined behavior in older implementations of the C library.

Example

#include

int main(void) { FILE *file_pointer; int i; file_pointer = fopen("text.txt", "wt"); for (i = 0; i < 100; i++) { fprintf(file_pointer, "Line %d ", i); fflush(file_pointer); } fclose(file_pointer); return 0;}This program code creates a file called "text.txt" and writes 100 strings of the form "Line " to it, flushing the buffer after each write.

External links

* [http://c-faq.com/stdio/stdinflush.html comp.lang.c FAQ list · Question 12.26a]
*

See also

* fclose
* setvbuf