Extract specific information from file C++

Question

I'm trying to read a file using c++ but I am only looking to store certain things. This is what my file looks like

stufff
stuff
more stuff
    .
    .
    .
data_I_want 32 34 45
data_I_want 52 22 34
stuff again
    .
    .
    .
end of file

So far I have written this code, but the output is always 0.

ifstream file;
file.open("stuff.txt");
string line;
double v;
if(file.is_open()){
    while(getline(file,line) && line.compare("data_I_want")){
            file>>v;
            cout<<v<<endl;
    }
    file.close();
}

Answer 1

line is data_I_want 32 34 45, not just data_I_want. May be you want to find lines starting with data_I_want

And here is how you use get substring of a string (taken from here):

// string::substr
#include <iostream>
#include <string>

int main ()
{
  std::string str="We think in generalities, but we live in details.";
                                           // (quoting Alfred N. Whitehead)

  std::string str2 = str.substr (12,12);   // "generalities"

  std::size_t pos = str.find("live");      // position of "live" in str

  std::string str3 = str.substr (pos);     // get from "live" to the end

  std::cout << str2 << ' ' << str3 << '\n';

  return 0;
}