Part9 模板与群体数据 9.1模板

//例：求绝对值函数的模板
#include<iostream>
using namespace std;
template<typename T>
T abs(T x){
    return x < 0 ? -x : x;
}
int main(){
    int n = -5;
    double d = -5.5;
    cout << abs(n) << endl;
    cout << abs(d) << endl;
    return 0;
}

//9-1函数模板的示例
#include<iostream>
using namespace std;
template<class T>
void outputArray(const T *array, int count){
    for(int i = 0; i < count;i++)
        cout << array[i] << " ";
    cout << endl;
}
int main(){
    const int A_COUNT = 8, B_COUNT = 8, C_COUNT = 20;
    int a[A_COUNT] = {1,2,3,4,5,6,7,8};
    double b[B_COUNT] = {1.1,2.2,3.3,4.4,5.5,6.6,7.7,8.8};
    char c[C_COUNT] = "Welcome!";
    
    cout << "a array contains: " << endl;
    outputArray(a, A_COUNT);
    cout << "b array contains: " << endl;
    outputArray(b, B_COUNT);
    cout << "c array contains: " << endl;
    outputArray(c, C_COUNT);
    return 0;
}

//例9-2 类模板示例
#include<iostream>
#include<cstdlib>
using namespace std;
struct Student{
    int id;
    float gpa;
};
template<class T>
class Store{//类模板：实现对任意类型数据进行存取
private:
    T item;
    bool haveValue;
public:
    Store();
    T &getElem();//提取数据函数
    void putElem(const T &x);//存入数据函数
};

template<class T>
Store<T>::Store():haveValue(false){}
template<class T>
T &Store<T>::getElem(){
    //如果试图提取未初始化的数据，则终止程序
    if(!haveValue){
        cout << "No item present!" << endl;
        exit(1); //使程序完全退出，返回到操作系统
    }
    return item;
}
template<class T>
void Store<T>::putElem(const T &x){
    haveValue = true;
    item = x;
}

int main(){
    Store<int> s1, s2;
    s1.putElem(3);
    s2.putElem(-7);
    cout << s1.getElem() << " " << s2.getElem() << endl;
    
    Student g = {1000,23};
    Store<Student> s3;
    s3.putElem(g);
    cout << "The student id is " << s3.getElem().id << endl;
    
    Store<double> d;
    cout << "Retrieving object D...";
    cout << d.getElem() << endl;//d未初始化
    return 0;
}