函數模板

函數模板

一個函數模板就是一個創建函數的藍圖或者公式。

例如，我們希望編寫一個函數來比較兩個值（值類型可能爲int型、double型、string型……），由於值類型繁多，所以我們必須編寫多個函數，每個函數比較一種給定類型的值。

但是，如果我們使用函數模板，通過函數模板這個藍圖生成針對特定類型的函數版本，那我們的工作量將大大減少。

#include <iostream>

using namespace std;

template <typename T>
void Swap(T &a , T &b)
{
    T temp;
    temp = a;
    a = b;
    b = temp;
}

int main() {
    int i = 10;
    int j = 20;
    cout << "Original:" << endl;
    cout << "i = " << i << "j = " << j << endl;
    Swap(i , j);
    cout <<"Swapped: " << endl;
    cout << "i = " << i << "j = " << j << endl;

    double m = 10.10;
    double n = 20.20;
    cout << "Original:" << endl;
    cout << "m = " << m << "n = " << n << endl;
    Swap(m , n);
    cout <<"Swapped: " << endl;
    cout << "m = " << m << "n = " << n << endl;
}

函數模板與重載

#include <iostream>

using namespace std;

const int Lim = 8;

template <typename T>
void Swap(T &a , T &b)
{
    T temp;
    temp = a;
    a = b;
    b = temp;
}

template <typename T>
void Swap(T a[] , T b[] , int n)
{
    T temp;
    for (int i = 0; i < n; ++i) {
        temp = a[i];
        a[i] = b[i];
        b[i] = temp;
    }
}


void show(int a[])
{
    cout << a[0] << a[1] << "/";
    cout << a[2] << a[3] << "/";
    for (int i = 4; i < Lim ; ++i)
        cout << a[i];
    cout << endl;
}

int main() {
    int i = 10;
    int j = 20;
    cout << "i = " << i << "j = " << j << endl;
    Swap(i , j);
    cout << "i = " << i << "j = " << j << endl;

    int d1[Lim] = {0,7,0,4,1,7,7,6};
    int d2[Lim] = {0,7,2,0,1,9,6,9};
    show(d1);
    show(d2);
    Swap(d1 , d2 , Lim);
    show(d1);
    show(d2);
}

顯示具體化模板函數

#include <iostream>

using namespace std;

struct job
{
    char name[40];
    double salary;
    int floor;
};

template <typename T>
void Swap(T &a , T &b)
{
    T temp;
    temp = a;
    a = b;
    b = temp;
}

template <> void Swap<job> (job &j1 , job &j2)
{
    double t1;
    int t2;

    t1 = j1.salary;
    j1.salary = j2.salary;
    j2.salary = t1;

    t2 = j1.floor;
    j1.floor = j2.floor;
    j2.floor = t2;
}

void show(job &j)
{
    cout << j.name << ": $" << j.salary << " on floor " << j.floor << endl;
}

int main()
{
    int i = 10 , j = 20;
    cout << " i , j = " << i << "," << j << endl;
    Swap(i , j);
    cout << " i , j = " << i << "," << j << endl;

    job sue = {"susan yaffe" , 73000.60 , 7};
    job sidney = {"sidney taffe" , 78060.72 , 9};
    show(sue);
    show(sidney);
    Swap(sue , sidney);
    show(sue);
    show(sidney);
}

再探模板函數