Mega Code Archive
Sqrt
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/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
// primary template: yield second or third argument depending on first argument
template<bool C, typename Ta, typename Tb>
class IfThenElse;
// partial specialization: true yields second argument
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb> {
public:
typedef Ta ResultT;
};
// partial specialization: false yields third argument
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb> {
public:
typedef Tb ResultT;
};
// template to yield template argument as result
template<int N>
class Value {
public:
enum { result = N };
};
// template to compute sqrt(N) via iteration
template <int N, int I=1>
class Sqrt {
public:
// instantiate next step or result type as branch
typedef typename IfThenElse<(I*I<N),
Sqrt<N,I+1>,
Value<I>
>::ResultT
SubT;
// use the result of branch type
enum { result = SubT::result };
};
int main()
{
std::cout << "Sqrt<16>::result = " << Sqrt<16>::result << std::endl;
std::cout << "Sqrt<25>::result = " << Sqrt<25>::result << std::endl;
std::cout << "Sqrt<42>::result = " << Sqrt<42>::result << std::endl;
std::cout << "Sqrt<1>::result = " << Sqrt<1>::result << std::endl;
}
Sqrt::result = 4
Sqrt::result = 5
Sqrt::result = 7
Sqrt::result = 1
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