How to check if string ends with .txt

Question

I am learning basic C++, and right now I have gotten a string from a user and I want to check if they typed the entire file name (including .txt) or not. I have the string,

Answer 1

bool has_suffix(const std::string &str, const std::string &suffix)
{
    std::size_t index = str.find(suffix, str.size() - suffix.size());
    return (index != std::string::npos);
}