Converting an Arbitrary Type to String
Our first function template takes a value of an arbitrary type T, converts it to string, and writes the result to a user-supplied string called val. We use the stringstream::str() member function to obtain a copy of the stream's internal string:

#include <sstream>
#include <string>
using namespace std;
template <class T>
void string_fmt(string & val, const T & t)
{
 ostringstream oss; // create a stream
 oss << t; // insert value to stream 
 val=oss.str(); // extract string and copy 
}

In the following example, we use the string_fmt() function template to convert the value 10.76 to string and write the result to val:

string val;
string_fmt(val,10.76);

Converting from One Arbitrary Type to Another
Our second function template is called cast_stream(). It converts a variable of type in_value to a variable of type out_type (in_value and out_value are template parameters):

template <class out_type, class in_value>
out_type cast_stream(const in_value & t)
{
 stringstream ss;
 ss << t; // first insert value to stream
 out_type result; // value will be converted to out_type
 ss >> result; // write value to result
 return result;
}

In the following example, cast_stream() converts a string with the value "18.67" to double using cast_stream():

string s="18.67";
double d=cast_stream < double > (s); // assign 18.67 to d