友元函数

 1 // 比如
 2 //
 3 // 这段实现了重载操作符 String + char* 的操作
 4 
 5 const char* operator+(const char* str) {
 6     int len = 0;
 7     if( str )
 8         len = strlen(str);
 9     if(pTmpString)
10         delete pTmpString;
11 
12     int oldlen = strlen(pString);
13     pTmpString = new char[oldlen+len+1];
14     pTmpString[oldlen+len] = 0;
15     wsprintfA(pTmpString,"%s%s",pString,str);
16     return pTmpString;
17 }
18 

19 //
20 // 但是如果想实现 char* + String 的操作就必须使用友元函数了
21 //
22 // 因为他可以直接访问类里的私有数据
23 
24 friend const char* operator+(const char* str,String &strclass) {
25     int len = 0;
26     if( str )
27         len = strlen(str);
28     if(strclass.pTmpString)
29         delete strclass.pTmpString;
30 
31     int oldlen = strlen(strclass.pString);
32     strclass.pTmpString = new char[oldlen+len+1];
33     strclass.pTmpString[oldlen+len] = 0;
34     wsprintfA(strclass.pTmpString,"%s%s",str,strclass.pString);
35     return strclass.pTmpString;
36 }