C++第59课--类模板深度剖，类模板的特化，函数模板的特化

本文学习自 狄泰软件学院 唐佐林老师的 C++课程，文中图片源自老师课程PPT。

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实验1：类模板的特化
实验2：特化的深入理解：函数模板的完全特化

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实验1：类模板的特化

#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
{
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 >    //部分特化， 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;
    }
};

template
<  >
class Test < void*, void* >    // 完全特化，当 T1 == void* 并且 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;
    }
};

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;
}

mhr@ubuntu:~/work/c++$ 
mhr@ubuntu:~/work/c++$ g++ 59-1.cpp
mhr@ubuntu:~/work/c++$ ./a.out 
void add(T1 a, T2 b)
3.5
void add(T a, T b)
10
class Test < T, T >
void add(void* a, void* b)
Error to add void* param...
void add(T1* a, T2* b)
1.1
mhr@ubuntu:~/work/c++$ 

类模板的特化实现在表面上好像是我们定义了不同的类模板，但是其实不是，我们仅仅是根据需要将一个类模板分开成不同的情况来实现。

实验2：特化的深入理解：函数模板的完全特化

#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;
    }
};

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);
}

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;
    
	//编译器回优先的选择全局的重载函数。
    //cout << Equal( 0.001, 0.001 ) << endl;// cout << "bool Equal(double a, double b)" << endl;
    
     cout << Equal<>( 0.001, 0.001 ) << endl;//放弃全局重载函数，只使用函数模板。
     
    return 0;
}

mhr@ubuntu:~/work/c++$ g++ 59-2.cpp
mhr@ubuntu:~/work/c++$ ./a.out 
bool Equal(T a, T b)
1
bool Equal<double>(double a, double b)
1
mhr@ubuntu:~/work/c++$