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

Here is the "fully self-written" solution:

bool isEndsWith(const std::string& pstr, const std::string& substr) const
{
    int tlen = pstr.length();
    int slen = substr.length();

    if(slen > tlen)
        return false;

    const char* tdta = pstr.c_str();
    const char* sdta = substr.c_str();

    while(slen)
    {
        if(tdta[tlen] != sdta[slen])
            return false;

        --slen; --tlen;
    }
    return true;
}