File handling in C++ works almost identically to terminal input/output. To use files, you write #include <fstream> at the top of your source file. Then you can access two classes from the std namespace:

• ifstream – allows reading input from files 
• ofstream – allows outputting to files

Each open file is represented by a separate ifstream or an ofstream object. You can use
ifstream objects in excatly the same way as cin and ofstream objects in the same way as cout, except that you need to declare new objects and specify what files to open. For example:

# include
<fstream >

using
namespace std ;

int main ()
{
ifstream
source (" source -file . txt ");
ofstream
destination ("dest -file .txt");
int x;
source >> x;
source . close ();
destination << x;

return 0;

}
close ()

As an alternative to passing the filename to the constructor, you can use an existing ifstream or ofstream object to open a file by calling the open method on it: source.open("other-file.txt");.
Close your files using the close() method when you’re done using them. This is automatically done for you in the object’s destructor, but you often want to close the file ASAP, without waiting for the destructor.

You can specify a second argument to the constructor or the open method to specify what “mode” you want to access the file in – read-only, overwrite, write by appending, etc. Check documentation online for details.
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