Convert char* to abitrary numeric type without using stringstream

I'd like to be able to convert a char* to an arbitrary numeric type T Similar to below, but without using the stringstream library, and obviously that one uses the string type which I don't want to use either.

How would I go about doing this?

e.g.

template<class T>
T string_as_T( const string& s )
{
    // Convert from a string to a T
    // Type T must support >> operator
    T t;
    std::istringstream is开发者_开发知识库t(s);
    ist >> t;
    return t;
}

---

Traits?

 template<class T>
 char* fmt(T value) { throw new /*some exception, or return null*/; }

 char* fmt<int>(int value) { return "%d"; } // forgive rusty specialization syntax
 // write fmt<double>, char, float, long, etc

 template<class T>
 T string_as_T( const char* s )
 {
     T val;
     sscanf(s, fmt(val), &val);
     return val;
 }

---

You can use boost.conversion, lexical_cast to achieve this.

#include "boost/lexical_cast.hpp"  

char* string = "15";
int output = 0;
output = boost::lexical_cast<INT_TYPE>(string);