42 lines
1.1 KiB
C++
42 lines
1.1 KiB
C++
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#include <iostream>
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using namespace std;
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// 前置声明，否则会报错，因为下面的友元函数模版中使用了Pair模版
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template <typename T1, typename T2>
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class Pair;
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template <typename T1, typename T2>
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ostream &operator<<(ostream &out, const Pair<T1, T2> &p);
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template <typename T1, typename T2>
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class Pair
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{
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// 使用外部实现友元函数的方式，需要添加<>空泛型标识，否则编译器会认为是重复声明
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friend ostream &operator<<<>(ostream &out, const Pair<T1, T2> &p);
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private:
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T1 first;
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T2 second;
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public:
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Pair(T1 f, T2 s) : first(f), second(s) {}
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T1 getFirst() const { return first; }
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T2 getSecond() const { return second; }
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};
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template <typename T1, typename T2>
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ostream &operator<<(ostream &out, const Pair<T1, T2> &p)
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{
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out << p.getFirst() << " " << p.getSecond();
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return out;
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}
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int main()
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{
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Pair<string, int> p1 = Pair<string, int>("x", 20);
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Pair<string, string> p2 = Pair<string, string>("name", "disen");
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// cout << p1 << endl;
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cout << p1 << "," << p2 << endl;
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return 0;
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}
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