在模板类中专门设置friend运算符之前定义的错误

I tried to specialize << operator for char in my template class

我试图在我的模板类中专门化<< operator for char

hpp

template<class T>
class tablicowy{
public:
    T * tablica;
    int rozmiar;
public:
    tablicowy(T arr[], int n){
        {
            tablica = arr;
            rozmiar = n;
        }
    };
    friend std::ostream& operator<<(std::ostream& out, tablicowy<char>& that );
    friend std::ostream& operator<<(std::ostream& out, tablicowy<T>& that ){
        out << "( ";
        for(int i = 0; i < that.rozmiar; i++){
            out << that.tablica[i] << comma;
        }
        out << ")";
        return out;
    };

};

cpp

std::ostream& operator<<(std::ostream& out, tablicowy<char>& that ){
    out << "'";
    for(int i = 0; i < that.rozmiar; i++){
        out << that.tablica[i];
    }
    out << "'";
    return out;
};

C++ give me :

C ++给我:

In file included from /home/pawel/ClionProjects/lista9/obliczenia.cpp:1:0: /home/pawel/ClionProjects/lista9/obliczenia.hpp: In instantiation of ‘class obliczenia::tablicowy’: /home/pawel/ClionProjects/lista9/obliczenia.cpp:38:28: required from here /home/pawel/ClionProjects/lista9/obliczenia.hpp:40:30: error: redefinition of ‘std::ostream& obliczenia::operator<<(std::ostream&, obliczenia::tablicowy&)’ friend std::ostream& operator<<(std::ostream& out, tablicowy& that ){ ^ /home/pawel/ClionProjects/lista9/obliczenia.cpp:36:15: error: ‘std::ostream& obliczenia::operator<<(std::ostream&, obliczenia::tablicowy&)’ previously defined here std::ostream& operator<<(std::ostream& out, tablicowy& that ){

在/home/pawel/ClionProjects/lista9/obliczenia.cpp:1:0中包含的文件:/home/pawel/ClionProjects/lista9/obliczenia.hpp:在'class obliczenia :: tablicowy'的实例化中:/ home / pawel / ClionProjects / lista9 / obliczenia.cpp:38:28:从这里需要/home/pawel/ClionProjects/lista9/obliczenia.hpp:40:30:错误:重新定义'std :: ostream&obliczenia :: operator <<(std: :ostream&,obliczenia :: tablicowy&)'friend std :: ostream&operator <<(std :: ostream&out,tablicowy&that){^ /home/pawel/ClionProjects/lista9/obliczenia.cpp:36:15:error:'std :: ostream&obliczenia :: operator <<(std :: ostream&,obliczenia :: tablicowy&)'先前在此定义std :: ostream&operator <<(std :: ostream&out,tablicowy&that){

What can i do to overload or specialize that operator for char?

我可以做什么来重载或专门化该运算符的char?

2 个解决方案

#1

You may use the following:

您可以使用以下内容:

// Forward declare the class
template <typename T> class tablicowy;

// Forward declare the template operator
template <typename T>
std::ostream& operator<<(std::ostream& out, tablicowy<T>& that );

// Forward declare the function
std::ostream& operator<<(std::ostream& out, tablicowy<char>& that );

// Your class:
template<class T>
class tablicowy{
public:
    T * tablica;
    int rozmiar;
public:
    tablicowy(T arr[], int n){
        {
            tablica = arr;
            rozmiar = n;
        }
    };
    // just declare them friend.
    friend std::ostream& operator<<(std::ostream& out, tablicowy<char>& that );
    friend std::ostream& operator<< <>(std::ostream& out, tablicowy<T>& that );

};

// Implementation
template <typename T>
std::ostream& operator<<(std::ostream& out, tablicowy<T>& that )
{
    const std::string comma = ",";
    out << "( ";
    for(int i = 0; i < that.rozmiar; i++){
        out << that.tablica[i] << comma;
    }
    out << ")";
    return out;
}

And in cpp:

并在cpp:

std::ostream& operator<<(std::ostream& out, tablicowy<char>& that ){
    out << "'";
    for(int i = 0; i < that.rozmiar; i++){
        out << that.tablica[i];
    }
    out << "'";
    return out;
}

[https://ideone.com/SXClzp](Live example)

#2

Try adding template <> before friend std::ostream& operator<<(std::ostream& out, tablicowy<char>& that ); to indicate it is a Template Specialization

尝试在朋友std :: ostream&operator < <之前添加模板<> (std :: ostream&out,tablicowy &that);表明它是模板专业化

You will also need to move implementation of friend class outside of class - see Explicit specialization of friend function for a class template for details

您还需要在类之外移动友元类的实现 - 有关详细信息,请参阅类模板的朋友函数的显式特化

#1