freopen() - I/O Function

How is "freopen()" used in C++?


freopen() is an I/O function that is used to associate an existing stream with another file. This function returns a pointer to the stream on success, a null pointer otherwise.


FILE *freopen( const char *fname, const char *mode, FILE *stream);

Following table lists the different modes used by this function.
Mode Description
r Open the text file for reading.
w Create a text file for writing.
a Append to a file
r+ Open a file for both reading and writing.
w+ Create a empty file for reading and writing
a+ Open a file forreading and appending.

Example :

#include <stdio.h>
int main ()
freopen ("freopeneg.txt","w",stdout);
printf ("This text is redirected to freopeneg.txt.");
fclose (stdout);
return 0;

Result :

This text is redirected to freopeneg.txt

In the above example the "freopen()" is used redirect a standard output stream to write a text.

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