C2079 'stream' uses undefined class 'std::basic_ifstream<char,std::char_traits<char>>'

First, make sure you have included the necessary header file for input/output operations:

#include <fstream>

Then, declare an object of type std::ifstream:

std::ifstream fileStream;

Ensure that you have access to the file you are trying to open and that the file path is correctly provided:

fileStream.open("example.txt");