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

1 #include <iostream>
2 #include <stdio.h>
3
4 using namespace std;
5
6 class String {
7 public:
8     String(const char *pdata);
9     String(const String &rhs);
10     String &operator = (const String &rhs);
11     ~String();
12
13 public: //应该使用private,但为了演示的目的而使用public
14     //内部类
15     class StringValue {
16     public:
17         StringValue(const char *pdata);
18         ~StringValue();
19     public:
20         int refCount;
21         char *data;
22     };
23
24     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
25 };
26
27 String::StringValue::StringValue(const char *pdata):refCount(1) {
28     data = new char[strlen(pdata) + 1];
29     strcpy(data,pdata);
30 }
31
32 String::StringValue::~StringValue() {
33     delete [] data;
34 }
35
36 String::String(const char *pdata) : value(new StringValue(pdata)) {}
37
38 String::String(const String &rhs) {//要对引用加1
39     value = rhs.value;
40     (value->refCount)++;//所有指向同一段data的对象的引用加1
41 }
42
43 String &String::operator =(const String &rhs) {
44     if (value == rhs.value)//注意，不是this == &rhs
45         return *this;
46     if(--value->refCount == 0)
47     {
48         printf("operator =[delete value] value->refCount=%d\n",value->refCount);
49         delete value;
50     }
51
52     value = rhs.value;
53     ++(value->refCount);
54
55     return *this;
56 }
57
58 String::~String() {
59     if ( (--value->refCount) == 0 )
60     {
61         printf("~String():[delete value] value->refCount=%d\n",value->refCount);
62         delete value;
63     }
64     else
65     {
66         printf("~String(): value->refCount=%d\n",value->refCount);
67     }
68 }
69
70 void test() {
71     String ss("ssss");
72     printf("ss.value->refCount=%d\n",ss.value->refCount);
73     String s1 = ss;
74     printf("s1.value->refCount=%d\n",s1.value->refCount);
75     printf("ss.value->refCount=%d\n",ss.value->refCount);
76     String s2("dddd");
77     printf("s2.value->refCount=%d\n",s2.value->refCount);
78     s2 = ss;
79     printf("s2.value->refCount=%d\n",s2.value->refCount);
80     printf("ss.value->refCount=%d\n",ss.value->refCount);
81 }
82
83 int main() {
84     test();
85 }

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