#include <iostream>
#include <string>
#include <sstream>

template <typename In_type, typename Out_type>
Out_type Convert(const In_type &value) {
    Out_type out;
    std::stringstream s;
    s << value;
    s >> out;
    return out;
}

int main() {
    std::string strNum = "1234";
    int dNum = Convert<std::string, int>(strNum);
    std::cout << strNum << " == " << dNum << std::endl;

    std::cout << "Enter a floating point value: ";
    float fNum;
    std::cin >> fNum;
    std::string strFloat = Convert<float, std::string>(fNum);
    std::cout << fNum << " == " << strFloat << std::endl;

    return 0;
}

Output:

1234 == 1234
Enter a floating point value: 481.3
481.3 == 481.3

That is interesting about the mixing of str() and the << operator. Doing so is kind of like mixing metaphors though — better to stick with one or the other.

There is an error in the section Clearing a stringstream for reuse. The second suggestion of using erase does not work. I think this is because os.str() returns a copy of the buffer and erase then just erases the copy leaving the original in tact. So the code in this case will still print “Hello World!”

Another point to note is that setting a buffer using str(“xx”) and then using the << operator on the stream will not append (as I at first thought) but will overwrite. So the following code:

stringstream os;
os.str("xxxxxxxxxx");
os << "World!";
cout << os.str() << endl;

will output:

World!xxxx

Second you need to include < sstream > to get at stringstream.

Third, the behaviour of >> and str() is subtly different as shown by this code:

stringstream os;
os << "12345 67.89"; // insert a string of numbers into the stream
string strValue;
os >> strValue; // extract 1st value
cout << "value1 " << strValue << endl;
os >> strValue; // extract 2nd value
cout << "value2 " << strValue << endl;
cout << "whole string " << os.str() << endl; // print whole string!

which gives the following output:

value1 12345
value2 67.89
whole string 12345 67.89

In other words the >> operator takes values from the string, moving along every time it is used, but the str() function always returns the whole string no matter how many times it is called (even after using >>)