C Language - fflush() : flush stream

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; } }