一个c++模板问题，请大家帮忙看看

[naturalpower1983]

#include<iostream>
using namespace std;
template<class elemType>
class Examples{
public:
explicit Examples(elemType val=0)
:_val(val){}
bool min(elemType value){return _val<value;}
void value(elemType new_val){_val=new_val;}
void print(ostream &os){os<<_val;}
private:
elemType _val;
};
template<class elemType>
ostream& operator<<(ostream &os,const Examples<elemType>&ex)
{
ex.print(os);
return os;
}
int main()
{
Examples<Examples<int>*> ex1;
Examples<int> sa(1024),sb;
sa=sb;
Examples<string> exs("walden");
//cout<<"exs:"<<exs<<endl;
return 0;
}
这样可以运行通过 但把注释的那句加上就报错
请高手指点

[chenyu2202863]

你把报错的提示给出来吧

[HewpKanXue]

改：
void print(ostream &os){os<<_val;}
--〉
void print(ostream &os) const {os<<_val;}

另外：min 这个函数名最好换一个，很多库里都已经有同名的了。
或者改成：
bool (min)(elemType value){return _val<value;}
用是可以，看着不顺眼。

[lzp729]

#include<iostream>
using namespace std;
template<class elemType>
class Examples{
public:
explicit Examples(elemType val=0)
:_val(val){}
bool min(elemType value){return _val<value;}
void value(elemType new_val){_val=new_val;}
void print(ostream &os){os<<_val;}
private:
elemType _val;
};
template<class elemType>
ostream& operator<<(ostream &os,Examples<elemType>&ex) // 去掉const
{
ex.print(os);
return os;
}
int main()
{
Examples<Examples<int>*> ex1;
Examples<int> sa(1024),sb;
sa=sb;
Examples<string> exs("walden");
cout<<"exs:"<<exs<<endl;
return 0;
}

[lzp729]

#include<iostream>
using namespace std;
template<class elemType>
class Examples{
public:
explicit Examples(elemType val=0)
:_val(val){}
bool min(elemType value){return _val<value;}
void value(elemType new_val){_val=new_val;}
void print(ostream &os)const {os<<_val;}//或者加个const
private:
elemType _val;
};
template<class elemType>
ostream& operator<<(ostream &os,const Examples<elemType>&ex)
{
ex.print(os);
return os;
}
int main()
{
Examples<Examples<int>*> ex1;
Examples<int> sa(1024),sb;
sa=sb;
Examples<string> exs("walden");
cout<<"exs:"<<exs<<endl;
return 0;
}

[lzp729]

to:HewpKanXue
类域是一个新的namespace 不会冲突

[HewpKanXue]

至少windows平台下，就有max/min的宏定义和你函数名冲突的。
你最好保佑你的程序没有包含有这些的文件。

[naturalpower1983]

E:\c++练习\moban.cpp(17) : error C2662: 'print' : cannot convert 'this' pointer from 'const class Examples<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >' to 'class Examples<class std::basic_string<char,str
uct std::char_traits<char>,class std::allocator<char> > > &'
Conversion loses qualifiers
E:\c++练习\moban.cpp(26) : see reference to function template instantiation 'class std::basic_ostream<char,struct std::char_traits<char> > &__cdecl operator <<(class std::basic_ostream<char,struct std::char_traits<char> > &,const class Examp
les<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > &)' being compiled
Error executing cl.exe.
这是报错信息
把const去掉也不行
报错如下：
E:\c++练习\moban.cpp(10) : error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' (or there is no acceptable conversion)
E:\c++练习\moban.cpp(10) : while compiling class-template member function 'void __thiscall Examples<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >::print(class std::basic_ostream<char,struct std::ch
ar_traits<char> > &)'
Error executing cl.exe.

[deng2000]

再加一个包含文件就行了:
#include<string>

[naturalpower1983]

非常感谢 本人太疏忽 不好意思