The **`fflush` function** is a C library function that flushes the output buffer of the stream.

> In the case of standard output, the output buffer is moved to the console. In the case of the file output stream, the output buffer is transferred to `disk`. 

In order to use the `fflush` function, the  `stdio` header file needs to be included in the program, as shown below:

``` C++
#include <stdio.h>
```


# Parameters

The function receives one parameter: a pointer to a `FILE` object that specifies a buffered stream.
# Return value

Upon successful execution of the function, zero is returned. End-of-File (EOF) is returned in case of any error, and the `error` indicator of the file stream is set.

# Example

The code below shows how the `fflush` function works in C++.

In line 9, the file is open for reading and writing. To do this, the stream is flushed after an output operation and before performing an input operation. This is done by explicitly calling the `fflush` function in line 11, as shown below:

#include <stdio.h>
#include <iostream>
using namespace std;

int main()
{
   char mybuffer[800];
   FILE * file;
   file = fopen ("demo.txt","r+");
   fputs ("test",file);
   fflush (file);    // flushing required
   fgets (mybuffer,800,file);
   cout << mybuffer << endl;
   fclose (file);
   return 0;
  
}

How to use fflush() in C++

The fflush function flushes the output buffer to the console or disk, requiring the stdio header and a FILE pointer.