Assigning the standard streams

This method of redirecting streams is known as direct assignment. You can redirect a C standard stream by assigning a valid file pointer to it, as follows:

    FILE *stream;
    stream = fopen("new.file", "w+");
    stdout = stream;

You must ensure that the streams are appropriate; for example, do not assign a stream opened for w to stdin. Doing so would cause a function such as getchar() called for the stream to fail, because getchar() expects a stream to be opened for read access.

Similarly, you can redirect a standard stream under C++ by assignment:

ofstream myfile("myfile.data");
cout = myfile;

Again, you must ensure that the assigned stream is appropriate; for example, do not assign an fstream opened for ios::out only to cin. This will cause a subsequent read operation to fail.