类友元函数模板

[dalookzhu]

template < class C >
class Complex{

	friend ostream& operator << <C>( ostream& output, const Complex< C > &a );
private:
	C real;
	C imag;
};

template < class C >
ostream& operator << ( ostream& output, const Complex< C > &a ){
	output << "real = " << a.real <<"\timag = " a.imag << endl;
	return output;
}

请问出什么问题了。

template < class C >
class Complex{

	friend ostream& operator << <C>( ostream& output, const Complex< C > &a );
private:
	C real;
	C imag;
};

template < class C >
ostream& operator << <C>( ostream& output, const Complex< C > &a ){
	output << "real = " << a.real <<"\timag = " a.imag << endl;
	return output;
}

我改成这样也错

[oyster2008]

template < class C > class Complex{ 
template <class U>
friend ostream& operator <<( ostream& output, const Complex< U > &a ); private: C real; C imag; }; template < class C > ostream& operator <<( ostream& output, const Complex< C > &a ){ output << "real = " << a.real <<"\timag = " a.imag << endl; return output; }

[oyster2008]

template < class C >
class Complex{
template <class U>
friend ostream& operator <<( ostream& output, const Complex< U > &a );
private:
C real;
C imag;
};
template < class C >
ostream& operator <<( ostream& output, const Complex< C > &a )
{
output << "real = " << a.real <<"\timag = " a.imag << endl;
return output;
}

[BuleRiver]

friend ostream& operator <<(ostream& output, const Complex< C > &a);

[dalookzhu]

[Quote=引用 2 楼 oyster2008 的回复:]
template < class C >
class Complex{
template <class U>
friend ostream& operator <<( ostream& output, const Complex< U > &a );
private:
C real;
C imag;
};
template < class C >
……
[/Quote]

我只想授予特定实例的友元函数

[耍宝王]

需要先声明这个模板友元函数

template < class C > class Complex;
template < class C > ostream& operator <<( ostream& output, const Complex< C > &a );//声明

template < class C >
class Complex{

    friend ostream& operator << <C>( ostream& output, const Complex< C > &a );
private:
    C real;
    C imag;
};

template < class C >
ostream& operator << ( ostream& output, const Complex< C > &a ){
    output << "real = " << a.real <<"\timag = " a.imag << endl;
    return output;
}

P.S 同时，请确认你用的不是VC6.0这类，对模板支持不佳的编译器

[dalookzhu]

[Quote=引用 5 楼 pgplay 的回复:]
需要先声明这个模板友元函数

C/C++ code
template < class C > class Complex;
template < class C > ostream& operator <<( ostream& output, const Complex< C > &a );//声明

template < class C >
class Co……
[/Quote]
是不是模板也一定要声明？

[pengzhixi]

template < class C >
class Complex;
template < class C >
ostream& operator << ( ostream& output, const Complex< C > &a );
template < class C >
class Complex{

    friend ostream& operator << <C>( ostream& output, const Complex< C > &a );
private:
    C real;
    C imag;
};

template < class C >
ostream& operator << ( ostream& output, const Complex< C > &a ){
    output << "real = " << a.real <<"\timag = " a.imag << endl;
    return output;
}

这样用

[dalookzhu]

[Quote=引用 7 楼 pengzhixi 的回复:]
C/C++ code

template < class C >
class Complex;
template < class C >
ostream& operator << ( ostream& output, const Complex< C > &a );
template < class C >
class Complex{

frie……
[/Quote]

error C2146: 语法错误 : 缺少“;”(在标识符“a”的前面)
1> .\2.cpp(39): 参见对正在编译的函数 模板 实例化“std::ostream &operator <<<C>(std::ostream &,const Complex<C> &)”的引用
1> with
1> [
1> C=int
1> ]
1>.\2.cpp(22) : error C2563: 在形参表中不匹配
1>.\2.cpp(22) : error C2568: “<<”: 无法解析函数重载
1> D:\Program Files\Microsoft Visual Studio 9.0\VC\include\ostream(974): 可能是“std::basic_ostream<_Elem,_Traits> &std::endl(std::basic_ostream<_Elem,_Traits> &)”
1> with
1> [
1> _Elem=wchar_t,
1> _Traits=std::char_traits<wchar_t>
1> ]
1> D:\Program Files\Microsoft Visual Studio 9.0\VC\include\ostream(966): 或 “std::basic_ostream<_Elem,_Traits> &std::endl(std::basic_ostream<_Elem,_Traits> &)”
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> D:\Program Files\Microsoft Visual Studio 9.0\VC\include\ostream(940): 或 “std::basic_ostream<_Elem,_Traits> &std::endl(std::basic_ostream<_Elem,_Traits> &)”
报错

[别逗我乐]

请楼主参照帖子 http://topic.csdn.net/u/20100612/13/9365495d-b1d8-4e87-b704-23895acb1637.html

[pengzhixi]

template < class C >
class Complex{

   template<class T> friend ostream& operator << ( ostream& output, const Complex< T > &a );
private:
    C real;
    C imag;
};

template < class T>
ostream& operator << ( ostream& output, const Complex< T > &a ){
    output << "real = " << a.real <<"\timag = " a.imag << endl;
    return output;
}

[耍宝王]

[Quote=引用 6 楼 dalookzhu 的回复:]

是不是模板也一定要声明？
[/Quote]
什么意思啊？

漏看一处
output << "real = " << a.real <<"\timag = " a.imag << endl;
改成
output << "real = " << a.real <<"\timag = " << a.imag << endl;

[pengzhixi]

template < class C >
class Complex{

    friend ostream& operator << ( ostream& output, const Complex< C > &a ){
output << "real = " << a.real <<"\timag = " a.imag << endl;
    return output;
}
       
private:
    C real;
    C imag;
};

我就还不信了 3种写法你的编译器都不支持。

[oyster2008]

什么意思，针对哪个特例
[Quote=引用 4 楼 dalookzhu 的回复:]

引用 2 楼 oyster2008 的回复:
template < class C >
class Complex{
template <class U>
friend ostream&amp; operator <<( ostream&amp; output, const Complex< U > &amp;a );
private:
C real;
C ……
[/Quote]

[dalookzhu]

。。。。。有朋友帮我解决了。。。。。。
是output << "real = " << a.real <<"\timag = " a.imag << endl;
这句错了。。。。。