Question

我正在尝试重载ostream和istream作为模板中类的freind。我已经在线查看，但是找不到关于模板重载的更多内容，我所看到的似乎也表明这是一个重要的方式来实现这些。很明显，我对编程非常陌生，并希望得到任何帮助。谢谢。

#include <stdio.h>
#include<vector>
#include<iostream>
using namespace std;
template<class T>
class MyClass

{
enter code here
public:
    MyClass();
    MyClass(const T& p_val1);
    MyClass(const MyClass<T>& p_val1);
    ~MyClass();
    MyClass<T>& operator=(MyClass<T>& rhs);

    friend ostream& operator<<(ostream& lhs, const MyClass<T> &printme);
    friend istream& operator>><T>(istream& lhs, MyClass<T>& readme);

private:
    T* m_val1;

};

实现ostream和istream。

template<class T>
ostream& operator<<(ostream&lhs, const MyClass<T>& printme)
{
    lhs << printme.m_val1;
    return lhs;
}
template<class T>
istream& operator>>(istream& lhs, MyClass<T>& readme)
{
    lhs >> *(readme.m_val1);
    return lhs;
}

这是错误

Undefined symbols for architecture x86_64:
  "MyClass<int>::~MyClass()", referenced from:
      _main in main.o
  "operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, MyClass<int> const&)", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

主要功能

  MyClass<int> a(8);
    MyClass<int> b(9);
    cout << " Enter a value for the two types to be swapped: ";
    cin >> a >> b;
    cout << "Before swapping...\n";
    cout << "Object a's pointer member dereferences a value of:\t" << a << endl;
    cout << "Object b's pointer member dereferences a value of:\t" << b << endl;

Answer 1

您正在声明您的运营商，但没有定义它们。模板定义与类中的模板定义无关，因为它们的原型不同，因此链接错误。将您的声明更改为：

template <typename T, typename Trait>
friend std::basic_ostream<T, Trait>&
operator<< (std::basic_ostream<T, Trait>& out, const MyClass& c)
{
    return out << c.my_val1;
}

template <typename T, typename Trait>
friend std::basic_istream<T, Trait>&
operator>> (std::basic_istream<T, Trait>& in, MyClass& c)
{
    return in >> *(c.my_val1);
}

请注意，它使用std::basic_ostream和std::basic_istream及其各自的类型和类型特征。它允许使用所有流，而不仅仅是std::ostream和std::istream。

将插入和提取操作符重载为模板

1 个答案: