结构体赋值的问题

ztkx

1. 
   
2. /*
   
3. * File:   main.cpp
   
4. * Author: zombo
   
5. *
   
6. * Created on 2009年6月25日, 上午8:54
   
7. */
   
8. 
   
9. #include <stdlib.h>
   
10. #include <iostream>
    
11. 
    
12. using namespace std;
    
13. 
    
14. typedef struct dam {
    
15.     int data;
    
16.     int len;
    
17. 
    
18.    void  operator()() {
    
19.         this->data = 0;
    
20.         this->len = 0;
    
21.     }
    
22. 
    
23. /*   void operator= ( dam value) {*/
    
24.            //this->data = value.data;
    
25.            //this->len = value.len;
    
26. /*   }*/
    
27.    dam& operator= (dam value) {
    
28.            this->data = value.data;
    
29.            this->len = value.len;
    
30.            return *this;
    
31.    }
    
32. 
    
33.    void print ( ) {
    
34.        cout << "data="<<this->data << "\tlen=" << this->len <<endl;
    
35.    }
    
36. 
    
37. } DAM, *PDAM;
    
38. 
    
39. typedef struct greendam {
    
40.     PDAM pvalue;
    
41.     //DAM value;
    
42. 
    
43.     void operator()() {
    
44.         pvalue = new dam();
    
45.     }
    
46. 
    
47.     greendam& operator= (greendam gdam) {
    
48.             this->pvalue = gdam.pvalue;
    
49.             return *this;
    
50.     }
    
51. 
    
52.     void print() {
    
53.             this->pvalue->print();
    
54.     }
    
55. 
    
56. 
    
57. } GDam, *PGDam;
    
58. 
    
59. /*
    
60. *
    
61. */
    
62. int main(int argc, char** argv) {
    
63. 
    
64.     PDAM as = new dam();
    
65. 
    
66.    PGDam pgDam = new greendam();
    
67.    GDam gdam;
    
68.    gdam.pvalue = new dam();
    
69. 
    
70.    gdam.print();  //正确
    
71.    pgDam->print();  //错误
    
72.    pgDam->pvalue->print();  // 错误
    
73. 
    
74.     return (EXIT_SUCCESS);
    
75. }
    
76. 
    
77. 
    

复制代码

结构体指针不能够实现正确的打印，但是，在重载函数里，已经生成一个新的结构体，并把指针传给它了

bruceteen

#include <iostream>

struct dam
{
        friend std::ostream& operator<<( std::ostream& os, const dam& d );
public:
        dam() : data_(0), len_(0)
        {
        }
        dam& operator=( const dam& rhs )
        {
                data_ = rhs.data_;
                len_ = rhs.len_;
                return *this;
        }
private:
        int data_;
        int len_;
};

std::ostream& operator<<( std::ostream& os, const dam& d )
{
        return os << "data=" << d.data_ << "\tlen=" << d.len_;
}

struct greendam
{
        friend std::ostream& operator<<( std::ostream& os, const greendam& d );
public:
        greendam() : pvalue_( new dam() )
        {
        }
        greendam( const greendam& rhs ) : pvalue_( new dam(*rhs.pvalue_) )
        {
        }
        greendam& operator=( const greendam& rhs )
        {
                if( this != &rhs )
                {
                        delete pvalue_;
                        pvalue_ = new dam( *rhs.pvalue_ );
                }
                return *this;
        }
        ~greendam()
        {
                delete pvalue_;
        }
private:
        dam* pvalue_;
};

std::ostream& operator<<( std::ostream& os, const greendam& d )
{
        return operator<<( os, *d.pvalue_ );
}


int main()
{
        using namespace std;

        dam a;
        cout << a << endl;

        greendam b;
        cout << b << endl;

        return 0;
}

ztkx

thanks