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() {
     data = new char[strlen(pdata) + ];
     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 == )
     {
         printf("operator =[delete value] value->refCount=%d\n",value->refCount);
         delete value;
     }  

     value = rhs.value;
     ++(value->refCount);  

     return *this;
 }  

 String::~String() {
     if ( (--value->refCount) ==  )
     {
         printf("~String():[delete value] value->refCount=%d\n",value->refCount);
         delete value;
     }
     else
     {
         printf("~String(): value->refCount=%d\n",value->refCount);
     }
 }  

 void test() {
     String ss("ssss");
     printf("ss.value->refCount=%d\n",ss.value->refCount);
     String s1 = ss;
     printf("s1.value->refCount=%d\n",s1.value->refCount);
     printf("ss.value->refCount=%d\n",ss.value->refCount);
     String s2("dddd");
     printf("s2.value->refCount=%d\n",s2.value->refCount);
     s2 = ss;
     printf("s2.value->refCount=%d\n",s2.value->refCount);
     printf("ss.value->refCount=%d\n",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