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C++：template(函数模板)

news 2025/5/14 0:03:46

基础使用

在使用函数的过程中可能会遇到同一个函数名被多次调用的情况，比如

#include <iostream>using namespace std;void Swap(int &i1,int &i2){int tmp;tmp = i1;i1 = i2;i2 = tmp;cout <<"交换后的整形1="<<i1<<"交换后的整形2="<<i2<<endl;
}
void Swap(double &d1,double &d2){double tmp;tmp = d1;d1 = d2;d2 = tmp;cout <<"交换后的浮点形1="<<d1<<"交换后的浮点形2="<<d2<<endl;
}
void Swap(string &s1,string &s2){string tmp;tmp = s1;s1 = s2;s2 = tmp;cout <<"交换后的字符串1="<<s1<<"交换后的字符串2="<<s2<<endl;
}
int main(){int a1 = 3, a2 = 4;double d1 = 3.5, d2 = 4.5;string s1 = "绿茶", s2 = "清补凉";Swap(a1,a2);Swap(d1,d2);Swap(s1,s2);
}

输出结果

交换后的整形1=4交换后的整形2=3
交换后的浮点形1=4.5交换后的浮点形2=3.5
交换后的字符串1=清补凉交换后的字符串2=绿茶

这样定义多个函数虽然也能实现想要的效果，但使用函数模板更加方便

#include <iostream>using namespace std;template<typename T>
void Swap(T &t1,T &t2){T tmp;tmp = t1;t1 = t2;t2 = tmp;cout <<"交换后的整形/浮点形/字符串1="<<t1<<"交换后的整形/浮点形/字符串2="<<t2<<endl;
}
int main(){int a1 = 3, a2 = 4;double d1 = 3.5, d2 = 4.5;string s1 = "绿茶", s2 = "清补凉";Swap(a1,a2);Swap(d1,d2);Swap(s1,s2);
}

输出结果

交换后的整形/浮点形/字符串1=4交换后的整形/浮点形/字符串2=3
交换后的整形/浮点形/字符串1=4.5交换后的整形/浮点形/字符串2=3.5
交换后的整形/浮点形/字符串1=清补凉交换后的整形/浮点形/字符串2=绿茶

这样大大节约了写代码的时间

假如传进去的数据类型不一样，则定义的函数模版需要两个typename

#include <iostream>using namespace std;template<typename T1, typename T2>
void Swap(T1 &t1,T2 &t2){cout <<t1<<"的价格是"  << t2 << endl;
}
int main(){int a1 = 3, a2 = 4;double d1 = 3.5, d2 = 4.5;string s1 = "绿茶", s2 = "清补凉";Swap(s1,a1);Swap(s2,a2);
}

函数模板还能为函数指定返回值，但要注意返回值要相同

#include <iostream>using namespace std;template<typename T1, typename T2>
T1 Swap(T1& t1, T2& t2) {cout << t1 << "的价格是" << t2 << endl;return t1;
}
int main(){int a1 = 3, a2 = 4;double d1 = 3.5, d2 = 4.5;string s1 = "绿茶", s2 = "清补凉";string ss1 = Swap(s1,a1);string ss2 = Swap(s2,a2);cout << ss1 << ss2 << endl;
}

输出结果

绿茶的价格是3
清补凉的价格是4
绿茶清补凉

函数模板的具体化

定义：可以提供一个具体化的函数定义，当编译器找到与函数调用匹配的具体化定义时，将使用该定义，不再寻找模板

假如传入类的对象可以这么写

#include <iostream>using namespace std;
class C {
public:string s;C(const string& ss) :s(ss) {}
};template<typename T1, typename T2>void Swap(T1& t1, T2& t2) {string c3 = t1.s;t1.s = t2.s;t2.s = c3;
}
int main(){C c1("绿茶");C c2("清补凉");cout << "交换前c1是" << c1.s << "c2是" << c2.s << endl;Swap(c1,c2);cout << "交换后c1是" << c1.s << "c2是" << c2.s << endl;
}

输出结果

交换前c1是绿茶c2是清补凉
交换后c1是清补凉c2是绿茶

但是当Swap要实现既能传入string也能传入类的对象时，需要具体化函数模板

#include <iostream>using namespace std;
class C {
public:string s;C(const string& ss) :s(ss) {}
};template<typename T1, typename T2>
void Swap(T1& t1, T2& t2) {string tmp = t1;t1 = t2;t2 = tmp;
}
template<>
void Swap<C>(C& t1, C& t2)//用尖括号指定的数据类型，不加其实也可以 
{
string c3 = t1.s;
t1.s = t2.s;
t2.s = c3;
}
int main() {C c1("绿茶");C c2("清补凉");string s1 = "绿茶";string s2 = "清补凉";cout << "交换前c1是" << c1.s << "c2是" << c2.s << endl;cout << "交换前s1是" << c1.s << "s2是" << c2.s << endl;Swap(c1, c2);Swap(s1, s2);cout << "交换后c1是" << c1.s << "c2是" << c2.s << endl;cout << "交换后s1是" << c1.s << "s2是" << c2.s << endl;
}

输出结果