C++ Extract number from the middle of a string

Question

I have a vector containing strings that follow the format of text_number-number

Eg: Example_45-3

I only want the first number (45 in the example) and nothing else which I am able to do with my current code:

std::vector<std::string> imgNumStrVec;
for(size_t i = 0; i < StrVec.size(); i++){
    std::vector<std::string> seglist;
    std::stringstream ss(StrVec[i]);
    std::string seg, seg2;
    while(std::getline(ss, seg, '_')) seglist.push_back(seg);
    std::stringstream ss2(seglist[1]);
    std::getline(ss2, seg2, '-');
    imgNumStrVec.push_back(seg2); 
}

Are there more streamlined and simpler ways of doing this? and if so what are they?

I ask purely out of desire to learn how to code better as at the end of the day, the code above does successfully extract just the first number, but it seems long winded and round-about.

Answer 1

You can also use the built in find_first_of and find_first_not_of to find the first "numberstring" in any string.

    std::string first_numberstring(std::string const & str)
    {
      char const* digits = "0123456789";
      std::size_t const n = str.find_first_of(digits);
      if (n != std::string::npos)
      {
        std::size_t const m = str.find_first_not_of(digits, n);
        return str.substr(n, m != std::string::npos ? m-n : m);
      }
      return std::string();
    }