To copy the contents of one file into another, use the fstream classes. First, open the source file using an ifstream object, then create a target file using ofstream, and finally, read the source into the target using the rdbuf() member function:
std::ifstream in ("oldfile.txt"); // open original file
std::ofstream out("newfile.txt"); // open target file
out << in.rdbuf(); // read original file into target
out.close(); // explicit close, unnecessary in this case
in.close();// explicit close, unnecessary in this case
Note that you don't have to call the close() member function because the fstream objects do that automatically when their destructors are invoked. However, you want to call close() if other parts of the program access the files before the fstream objects go out of scope.