c++模板类中怎么重载operator<<

rushrush

如题,我看的书上面没讲..我按自己的想法写了一个,结果编译不通过...
有人知道吗? thx

manphiz

模板类里重载operator<<？不太明白和普通类有什么区别？
而且operator<<作为成员存在没什么意义，一般作为全域函数，或者某类的friend。

rickxbx

Post by rushrush
如题,我看的书上面没讲..我按自己的想法写了一个,结果编译不通过...
有人知道吗? thx

如果有可能,把你的代码帖出来

rushrush

呃,是我没说清楚.是作为模板类的友员.
[PHP]
//testTempClass.h

#include <iostream>
using namespace std;

#ifndef H_testTempClass
#define H_testTempClass

template<class Type>
class testClass
{
        friend ostream& operator<<
                (ostream& osObj, const testClass<Type> &rightObj);
public:
        void setData(Type elem);
private:
        Type a;
};

template <class Type>
ostream& ostream& operator<<
                (ostream& osObj, const testClass<Type> &rightObj)
        //原来的testClass后面没有<Type>
{
        osObj<<rightObj.a;
        return osObj;
}

template <class Type>
void testClass<Type>::setData(Type elem)
{
        a = elem;
}

#endif

//main.cpp

#include "testTempClass.h"

int main()
{
        testClass<int> intObj;
        intObj.setData(2);
        cout<<intObj;
        cout<<endl;

        return 0;
}
[/PHP]

1. $ g++ -o test main.cpp
   
2. In file included from main.cpp:3:
   
3. testTempClass.h:13: warning: friend declaration `std::ostream&
   
4.    operator<<(std::ostream&, const testClass<Type>&)' declares a non-template
   
5.    function
   
6. testTempClass.h:13: warning: (if this is not what you intended, make sure the
   
7.    function template has already been declared and add <> after the function
   
8.    name here) -Wno-non-template-friend disables this warning
   
9. testTempClass.h:21: error: syntax error before `&' token
   
10. testTempClass.h:22: error: `Type' was not declared in this scope
    
11. testTempClass.h:22: error: template argument 1 is invalid
    
12. testTempClass.h:24: error: ISO C++ forbids declaration of `operator<<' with no
    
13.    type
    
14. testTempClass.h:24: error: ISO C++ forbids declaration of `rightObj' with no
    
15.    type
    
16. testTempClass.h: In function `int& operator<<(std::ostream&, const int&)':
    
17. testTempClass.h:25: error: request for member `a' in `rightObj', which is of
    
18.    non-class type `const int'
    
19. testTempClass.h:26: error: invalid initialization of reference of type 'int&'
    
20.    from expression of type 'std::basic_ostream<char, std::char_traits<char> >'

复制代码

还是错误,呵呵. 请大家多多指教..

rickxbx

呃,有点小问题,
[PHP]
//testTempClass.h

#include <iostream>
using namespace std;

#ifndef H_testTempClass
#define H_testTempClass

template<class Type>
class testClass
{
        friend ostream& operator<<
                (ostream& osObj, const testClass<Type> &rightObj);
[/php]
应该为:

1. 
   
2. template <typename T>
   
3. friend ostream& operator<<(ostream& osObj, const testClass<T> &rightObj);

复制代码

下面是笔误:
[php]
template <class Type>
ostream& ostream& operator<<
                (ostream& osObj, const testClass<Type> &rightObj)
        //原来的testClass后面没有<Type>
{
        osObj<<rightObj.a;
        return osObj;
}
[/php]
返回类型处多了一个ostream&

rushrush

编译成功
谢谢rickxbx