In C++, combination of ________ and _________ functions are used to determine the actual data length of a file.

In C++, combination of seekg() and tellg() functions are used to determine the actual data length of a file.

Here is a step by step guide:

1. Open the file in binary mode.
2. Use the seekg() function to move the get pointer to the end of the file. This function takes two arguments: the first is the number of positions to move (in this case, 0, because we want to move to the end), and the second is the position from where to move (in this case, ios::end, because we want to move from the end).
3. Use the tellg() function to get the position of the get pointer. This function returns the number of bytes from the beginning of the file to the current position of the get pointer, which is now at the end of the file. This number is the size of the file in bytes.
4. Don't forget to close the file after you're done.