帮我看看，友元，模板组合使用的问题？（可能还有缺省模板参数问题）

[wukexin]

#include <iostream>
using namespace std;
//
class Byte
{
public:
Byte(const unsigned char c):ch_(c) {};
protected:
friend std::ostream& operator<< (std::ostream& out,const Byte& b);
private:
unsigned char ch_;
};
//
std::ostream& operator<< (std::ostream& out,const Byte& b)
{
for (int i = 7; i >= 0; i--)
{
if ( b.ch_ & (1 << i) )
out << '1';
else
out << '0';
}
return out;
}
//
template <typename T>
class MemoryMap
{
public:
MemoryMap(const T& x):data_(x) {};
protected:
friend std::ostream& operator<< (std::ostream& out, MemoryMap<T>& x);
private:
T data_;
};
//
template<typename T>
std::ostream& operator<< (std::ostream& out,MemoryMap<T>& x)
{
MemoryMap<T>* ptr=&x.data_;
size_t length=sizeof(x.data_);
Byte* p=reinterpret_cast<Byte*>(ptr);
for (size_t i=0;i<length;i++)
{
out<<*p++<<' ';
if (i>4 && i%4=0 ) out<<'\n';
}
return out;
}
//

int main()
{std::string s="\00a";

cout << s<< endl;
MemoryMap<std::string> mm(s);
cout<< mm<<endl;
return 0;
}

[WaistCoat12]

啥问题啊？

[baihacker]

#include <iostream> 
using namespace std; 
// 
    class Byte 
    { 
    public: 
        Byte(const unsigned char c):ch_(c) {}; 
    protected: 
        friend std::ostream& operator << (std::ostream& out,const Byte& b); 
    private: 
        unsigned char ch_; 
    }; 
// 
    std::ostream& operator << (std::ostream& out,const Byte& b) 
    { 
        for (int i = 7; i >= 0; i--) 
        { 
            if ( b.ch_ & (1 << i) ) 
                out << '1'; 
            else 
                out << '0'; 
        } 
        return out; 
    } 
// 
 template <typename T> 
    class MemoryMap ;
    template <typename T> 
    std::ostream& operator << (std::ostream& out,MemoryMap <T>& x) ;
    
    template <typename T> 
    class MemoryMap 
    { 
    public: 
        MemoryMap(const T& x):data_(x) {}; 
    protected: 
        friend std::ostream& operator << <T>(std::ostream& out, MemoryMap <T>& x); 
    private: 
        T data_; 
    }; 
// 
    template <typename T> 
    std::ostream& operator << (std::ostream& out,MemoryMap <T>& x) 
    { 
        T* ptr=&x.data_; 
        size_t length=sizeof(x.data_); 
        Byte* p=reinterpret_cast <Byte*>(ptr); 
        for (size_t i=0;i <length;i++) 
        { 
            out <<*p++ <<' '; 
            if (i>4 && (i%4==0) ) out <<'\n'; 
        } 
        return out; 
    } 
// 

int main() 
{std::string s="\00a"; 

    cout << s << endl; 
    MemoryMap <std::string> mm(s); 
    cout << mm <<endl; 
    return 0; 
} 

[lsldd]

MemoryMap <T>* ptr=&x.data_;
这里要强转。

if (i>4 && i%4=0 ) out <<'\n';
-->if (i>4 && i%4==0 ) out <<'\n';

[likee003]

1、请问楼主有何问题？
2、判断语句不能够用赋值符号：

if (i>4 && i%4=0 ) out <<'\n';

[太乙]

#include <iostream>
using namespace std;
class Byte
{
    public:
        Byte(const unsigned char c):ch_(c) {};
    protected:
        friend std::ostream& operator << (std::ostream& out,const Byte& b);
    private:
        unsigned char ch_;
};
std::ostream& operator << (std::ostream& out,const Byte& b)
{
    for (int i = 7; i >= 0; i--)
    {
        if ( b.ch_ & (1 << i) )
          out << '1';
        else
          out << '0';
    }
    return out;
}
template <typename T>
class MemoryMap ;
template <typename T>
std::ostream& operator << (std::ostream& out,MemoryMap <T>& x) ;
template <typename T>
class MemoryMap
{
    public:
        MemoryMap(const T& x):data_(x) {};
    protected:
        friend std::ostream& operator << (std::ostream& out, MemoryMap <T>& x)
        {
            size_t length=sizeof(x.data_);
            Byte* p=reinterpret_cast <Byte*>(&x.data_);
            for (size_t i=0;i <length;i++)
            {
                out <<*p++ <<' ';
                if (i>4 && i%4==0 ) out <<'\n';
            }
            return out;

        }
    private:
        T data_;
};

int main()
{
    std::string s="\00a";
    cout << s << endl;
    MemoryMap <std::string> mm(s);
    cout << mm <<endl;
    return 0;


}

[wukexin]

谢谢各位大拿，我都迷惑了好几天了，原来关键问题是处在 MemoryMap <T>* ptr=&x.data_;
这里。

[wukexin]

为什么得到的结果，那么奇怪！（只有int类型结果可以理解）

int main()
{
char* s="0a";
WKX::MemoryMap<unsigned char> c1='0';
WKX::MemoryMap<unsigned char> c2='a';
WKX::MemoryMap<char*> mm(s);
cout<<
c1<<'\n'<<
c2<<'\n'<<
s<<'\t'<<
sizeof(char)<<'\t'<<
sizeof(s)<<'\t'<<
mm<<endl;
int x=5;
WKX::MemoryMap<int> i(x);
cout<<"sizeof(WKX::MemoryMap<int>)="<<sizeof(i)<<"\n"
<<x<<"=\n"<<i<<"\n";
WKX::MemoryMap<int> si(-x);
cout<<-x<<"=\n"<<si<<"\n";
float y=0.1;
WKX::MemoryMap<float> f(y);
cout<<"sizeof(WKX::MemoryMap<float>)="<<sizeof(f)<<"\n"
<<y<<"=\n"<<f<<"\n";
WKX::MemoryMap<double> d(y);
cout<<"sizeof(WKX::MemoryMap<float>)="<<sizeof(d)<<"\n"
<<static_cast<double>(y)<<"=\n"<<d<<"\n";
return 0;
}
／／结果：
00110000
01100001
0a 1 4 00000000 00110001 01000001 00000000
sizeof(WKX::MemoryMap<int>)=4
5=
00000101 00000000 00000000 00000000
-5=
11111011 11111111 11111111 11111111
sizeof(WKX::MemoryMap<float>)=4
0.1=
11001101 11001100 11001100 00111101
sizeof(WKX::MemoryMap<float>)=8
0.1=
00000000 00000000 00000000 10100000 10011001 10011001 10111001 00111111

[hoomien]

学习

[macrojj]

注意赋值左右的类型

[lovesi3344]

关注

[wukexin]

baihacker
不好意思，结贴时疏忽了。

[baihacker]

[Quote=引用 11 楼 wukexin 的回复:]
baihacker
不好意思，结贴时疏忽了。
[/Quote]
没关系.