Probably the best way is to read the entire file’s contents into a string, which can be done very easily using ifstream’s rdbuf() method:
std::ifstream in("myfile");
std::stringstream buffer;
buffer << in.rdbuf();
std::string contents(buffer.str());
You can then use regular string manipulation now that you’ve got everything from the file.
While Tomek was asking about reading a text file, the same approach will work for reading binary data, though the std::ios::binary flag needs to be provided when creating the input file stream.