The ****`freopen` function**** closes the old file in the given open stream and associates a new `filename` with this stream. It is written as follows:
```C
FILE *freopen(const char *filename, const char *mode, FILE *stream)
```

# Parameters
**`filename`** - the name of the file to be opened. This is a `C string`.

**`mode`** - `C string` containing a file access mode. Different file access modes are mentioned below:
| Mode|  Description |
| - | - |
| "r" |  Opens a file to be read. This file should already have been created. |
| "w"  | Creates an empty file that can be written to. If there is another file with the same name,then that is eradicated and this file is the empty file. |
| "a" | Adds contents to the end of a file. In case the file is not created already, then a new file is created first.  |
| "r+"  |  Opens a file to update it (both reading and writing). The file should already have been created. |
| "w+" | Creates a new empty file and opens it for update (both reading and writing). IIf there is another file with the same name,then that is eradicated and this file is the empty file..  |
| "a+" | Opens a file for update (both reading and appending).  |


# Return value
If the file was re-opened successfully, the function returns a pointer passed as the parameter `stream` that  identifies the reopened `stream`. Otherwise, `null pointer` is returned.

# Example
The following code shows the usage of the `freopen` function. After `freopen` is called, `stdout` is associated with the file `sampleFile.txt`. Therefore, whatever is written at `stdout` is written to `sampleFile.txt`:

#include <stdio.h>

int main () {
   freopen ("sampleFile.txt","w",stdout);
   printf ("This sentence will be moved to a file.");
   fclose (stdout);



   return(0);
}

After the execution of the code above, `sampleFile.txt` will contain the string at line 5.

What is freopen in C?

Reopens a file stream with a new filename, enabling file redirection in C programming.

Mode	Description
“r”	Opens a file to be read. This file should already have been created.
“w”	Creates an empty file that can be written to. If there is another file with the same name,then that is eradicated and this file is the empty file.
“a”	Adds contents to the end of a file. In case the file is not created already, then a new file is created first.
“r+”	Opens a file to update it (both reading and writing). The file should already have been created.
“w+”	Creates a new empty file and opens it for update (both reading and writing). IIf there is another file with the same name,then that is eradicated and this file is the empty file…
“a+”	Opens a file for update (both reading and appending).