stringstream >> assignment

[eric]

Dear advanced g++ program:

  I copied a simple template and streamstring code from book, c++
cookbook, at chapter 3 section 5.pg131: Parsing a string containing a
Number in Scientific Notation.
-----------------------------------------------------------
#include <iostream>
#include <sstream>
#include <string>

using namespace std;

//double sciToDub(const string& str) {
  template<typename T>
  T strToNum(const string& str) {
    

  stringstream ss(str);
  T tmp;
  ss >> tmp;

//  double d = 0;
//  ss >> d;
  if (ss.fail()){
    string s = "Unable to format ";
    s += str;
    s += " as a number!";
    throw(s);
  }
  return(tmp);
}
int main() {
  try {
   /*
    cout << sciToDub("1.23456789e5") << endl;
    cout << sciToDub("6.02987654e-5") << endl;
    cout << sciToDub("asdf")    << endl;
   */
   double d = strToNum<double>("7.0"); cout << d << endl;
   float f = strToNum<float>("7.0");   cout << f << endl;
   int i = strToNum<int>("7.0");       cout << i << endl;
   char c = strToNum<char>("7.0");     cout << c << endl;
  }
  catch (string& e) {
    cerr << "Whoops: " << e << endl;
  }
}
------------------------------------------------
my test result is all 4 output is 7
why is that, especially first two, double and float?
thanks your help a lot in advance, Eric