The fclose command can be used to disconnect a file pointer from a file. This is usually done so that the pointer can be used to access a different file. All systems have a limit on the number of files which can be open simultaneously, so it is a good idea to close a file when you have finished using it.
This would be done by a statement like
fclose(output_file);
If files are still open when a program exits, the system will close them for you automatically. However it is usually better to close the files properly.
