类模板深度剖析

Posted 2021-09-28 学习只为旅行

#include <iostream>
#include <string>

using namespace std;

template
< typename T1, typename T2 >
class Test
{
public:
    void add(T1 a, T2 b)
    {
        cout << "void add(T1 a, T2 b)" << endl;
        cout << a + b << endl;
    }
};

template
< typename T1, typename T2 >
class Test < T1*, T2* >      // 关于指针的特化实现
{
public:
    void add(T1* a, T2* b)
    {
        cout << "void add(T1* a, T2* b)" << endl;
        cout << *a + *b << endl;
    }
};

template
< typename T >
class Test < T, T >    // 当 Test 类模板的两个类型参数完全相同时，使用这个实现
{
public:
    void add(T a, T b)
    {
        cout << "void add(T a, T b)" << endl;
        cout << a + b << endl;
    }
    void print()
    {
        cout << "class Test < T, T >" << endl;
    }
};

//完全特化
template
<  >
class Test < void*, void* >    // 当 T1 == void* 并且 T2 == void* 时
{
public:
    void add(void* a, void* b)
    {
        cout << "void add(void* a, void* b)" << endl;
        cout << "Error to add void* param..." << endl;
    }
};

int main()
{  
    Test<int, float> t1;
    Test<long, long> t2;
    Test<void*, void*> t3;
    
    t1.add(1, 2.5);
    
    t2.add(5, 5);
    t2.print();
    
    t3.add(NULL, NULL);
    
    Test<int*, double*> t4;
    int a = 1;
    double b = 0.1;
    
    t4.add(&a, &b);
    
    return 0;
}

将一个类模板分成不同的情况来使用，并不是定义多个类模板！！

#include <iostream>
#include <string>

using namespace std;

template
< typename T1, typename T2 >
class Test
{
public:
    void add(T1 a, T2 b)
    {
        cout << "void add(T1 a, T2 b)" << endl;
        cout << a + b << endl;
    }
};

/*
template
<  >
class Test < void*, void* >    // µ± T1 == void* ²¢ÇÒ T2 == void* ʱ
{
public:
    void add(void* a, void* b)
    {
        cout << "void add(void* a, void* b)" << endl;
        cout << "Error to add void* param..." << endl;
    }
};
*/

class Test_Void
{
public:
    void add(void* a, void* b)
    {
        cout << "void add(void* a, void* b)" << endl;
        cout << "Error to add void* param..." << endl;
    }
};

template
< typename T >
bool Equal(T a, T b)
{
    cout << "bool Equal(T a, T b)" << endl;
    
    return a == b;
}

template
< >
bool Equal<double>(double a, double b)
{
    const double delta = 0.00000000000001;
    double r = a - b;
    
    cout << "bool Equal<double>(double a, double b)" << endl;
    
    return (-delta < r) && (r < delta);
}

//重载
bool Equal(double a, double b)
{
    const double delta = 0.00000000000001;
    double r = a - b;
    
    cout << "bool Equal(double a, double b)" << endl;
    
    return (-delta < r) && (r < delta);
}

int main()
{  
    cout << Equal( 1, 1 ) << endl;
    cout << Equal<>( 0.001, 0.001 ) << endl;
    //如果不加上<>，那么编译器优先选择全局重载函数！加上<>之后，只考虑函数模板
    
    return 0;
}

函数模板只能够完全特化，不能部分特化！

小结