C++简单实现对象引用计数示例（转）

C++简单实现对象引用计数示例

#include <iostream>  
#include <stdio.h>  
  
using namespace std;  
  
class String {  
public:  
    String(const char *pdata);  
    String(const String &rhs);  
    String &operator = (const String &rhs);  
    ~String();  
  
public: //应该使用private,但为了演示的目的而使用public  
    //内部类  
    class StringValue {  
    public:  
        StringValue(const char *pdata);  
        ~StringValue();  
    public:  
        int refCount;  
        char *data;         
    };  
  
    StringValue *value;//所有的引用对象均共享唯一一个value，value里面实际存储data和引用次数  
};  
  
String::StringValue::StringValue(const char *pdata):refCount(1) {  
    data = new char[strlen(pdata) + 1];  
    strcpy(data,pdata);  
}  
  
String::StringValue::~StringValue() {  
    delete [] data;  
}  
  
String::String(const char *pdata) : value(new StringValue(pdata)) {}  
  
String::String(const String &rhs) {//要对引用加1  
    value = rhs.value;  
    (value->refCount)++;//所有指向同一段data的对象的引用加1  
}  
  
String &String::operator =(const String &rhs) {  
    if (value == rhs.value)//注意，不是this == &rhs  
        return *this;  
    if(--value->refCount == 0)  
    {     
        printf("operator =[delete value] value->refCount=%d
",value->refCount);  
        delete value;  
    }  
  
    value = rhs.value;  
    ++(value->refCount);  
      
    return *this;  
}  
  
String::~String() {  
    if ( (--value->refCount) == 0 )  
    {     
        printf("~String():[delete value] value->refCount=%d
",value->refCount);  
        delete value;  
    }  
    else  
    {  
        printf("~String(): value->refCount=%d
",value->refCount);  
    }  
}  
  
void test() {  
    String ss("ssss");  
    printf("ss.value->refCount=%d
",ss.value->refCount);  
    String s1 = ss;  
    printf("s1.value->refCount=%d
",s1.value->refCount);  
    printf("ss.value->refCount=%d
",ss.value->refCount);  
    String s2("dddd");  
    printf("s2.value->refCount=%d
",s2.value->refCount);  
    s2 = ss;  
    printf("s2.value->refCount=%d
",s2.value->refCount);  
    printf("ss.value->refCount=%d
",ss.value->refCount);  
}  
  
int main() {  
    test();  
}  

运行结果如下：

ss.value->refCount=1
s1.value->refCount=2
ss.value->refCount=2
s2.value->refCount=1
operator =[delete value] value->refCount=0
s2.value->refCount=3
ss.value->refCount=3
~String(): value->refCount=2
~String(): value->refCount=1
~String():[delete value] value->refCount=0

转自：http://blog.csdn.net/chinawangfei/article/details/50680574