编译时的编程机制

来源：互联网发布：淘宝货物怎么上架编辑：程序博客网时间：2024/06/15 17:03

1.阶乘

template<int n> class Factorial{public:    enum{        val=Factorial<n-1>::val*n    };};template<> class Factorial<0>{public:    enum{        val=1       };};Factorial<>::val;       //120

2.斐波那契数列

template<int n> class Fib{public:    enum{        val=Fib<n-1>::val+Fib<n-2>::val    };};template<> class Fib<1>{public:    enum{        val=1       };};template<> class Fib<0>{public:    enum{        val=0       };};Fib<5>::val;        //5

3.N的P次方

template<int N,int P> class Power{public:    enum{        val=N*Power<N,P-1>::val    };};template<int N> class Power<N,0>{public:    enum{        val=1    };};Power<2,5>::val;        //32

4.f(n)+f(n-1)….f(0)

template<int n, template<int> typename F> class Accumulate {public:    enum {        val=Accumulate<n-1,F>::val+F<n>::val    };};template<template<int> typename F> class Accumulate<0, F> {public:    enum {        val=F<0>::val    };};template<int n> class Identity {public:    enum {        val=n    };};Accumulate<4, Identity>::val;       //10

5.循环分解，整数幂

template<int n> inline int power(int m){    return power<n-1>(m)*m;};template<> inline int power<1>(int m){    return m;};template<> inline int power<0>(int m){    return 1;};power<3>(4);        //64

6.编译时的条件选择：最大值

template<int n1,int n2> class Max{    enum{        val=n1>n2?n1:n2    };};Max<10,20>::val;        //20

7.表达式模板

template<class, std::size_t> class MyVectorSum;template<typename T, std::size_t N> class MyVector {private:    T data[N];public:    MyVector<T, N> &operator=(const MyVector<T, N> &right) {        for (std::size_t i = 0; i < N; ++i) {            data[i] = right.data[i];        }        return *this;    }    MyVector<T, N> &operator=(const MyVectorSum<T, N> &right);    const T &operator[](std::size_t i) const {        return data[i];    }    T &operator[](std::size_t i) {        return data[i];    }};template<typename T, std::size_t N> class MyVectorSum {private:    const MyVector<T, N> &left;    const MyVector<T, N> &right;public:    MyVectorSum(const MyVector<T,N> &lhs,const MyVector<T,N> &rhs):left(lhs),right(rhs){}    T operator[](std::size_t i) const {        return left[i] + right[i];    }};template<typename T, std::size_t N> MyVector<T, N> &MyVector<T, N>::operator=(const MyVectorSum<T, N> &right) {    for (std::size_t i = 0; i < N; ++i) {        data[i] = right[i];    }    return *this;}template<typename T,std::size_t N> inline MyVectorSum<T, N> operator+(const MyVector<T, N> &left, const MyVector<T, N> &right) {    return MyVectorSum<T, N>(left, right);}template<typename T,std::size_t N>void init(MyVector<T, N> &v) {    for (std::size_t i = 0; i < N; ++i) {        v[i] = rand() % 100;    }}template<typename T, std::size_t N> void print(MyVector<T, N> &v) {    for (std::size_t i = 0; i < N; ++i) {        std::cout << v[i] << ' ';    }    std::cout << endl;}void main() {    srand(time(0));    MyVector<int, 5> v1;    init(v1);    print(v1);    MyVector<int, 5> v2;    init(v2);    print(v2);    MyVector<int, 5> v3;    init(v3);    print(v3);    v3.operator=(MyVectorSum<int, 5>(v2, v3));}

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