看这个经典的NB 程序，求一个数有多少bit 。J

普通C++ 程序员

namespace traditional 

{ 

int bits_of(int remain) 

{ 

if (remain) 

return 1+bits_of( remain>>1 ); 

return 0; 

} 


int bits_of(void) 

{ 

return bits_of(~(int)0); 

} 

} 

文艺C++ 程序员

namespace modern 

{ 

template<int,typename THEN, typename ELSE> 

struct IF { typedefTHEN type; }; 


template<typename THEN, typename ELSE> 

struct IF<0,THEN,ELSE> { typedef ELSE type; }; 


template<typename T, T X> 

struct zero 

{ 

static const Tvalue = X; 

}; 


template<typename T, T X> 

struct bits_of 

{ 

typedef typenameIF<X, bits_of<T,(X>>1)>, zero<T,0> >::type type; 

static const Tvalue = type::value + !!X; 

}; 

}

还有文青的unit test，

typedef int a0[bits_of<int,0>::value==0? 1: -1];
typedef int a1[bits_of<int,1>::value==1? 1: -1];
typedef int a2[bits_of<int,2>::value==2? 1: -1];
typedef int a3[bits_of<int,3>::value==2? 1: -1];
typedef int a4[bits_of<int,4>::value==3? 1: -1];
typedef int a7[bits_of<int,7>::value==3? 1: -1];
typedef int a8[bits_of<int,8>::value==4? 1: -1];
typedef int a15[bits_of<int,15>::value==4? 1: -1];
typedef int a16[bits_of<int,16>::value==5? 1: -1];  

第三类C++ 程序员

namespace third_party 

{ 

// 您确定您能看懂？ ? ? 

}