more effective c++——Item M29 引用计数（一）简略的rfstring类设计和写时拷贝 这篇博客中所实现的引用计数还存在未解决的问题——如何通过相同的值多次构造rfstring对象时，防止多次在堆上分配内存？
可以通过在rfstring类中添加一个static list
// static_rfstring.h #pragma once #include <list> using namespace std; class static_rfstring { public: static_rfstring(const char *str); static_rfstring(const static_rfstring & rhl); static_rfstring & operator=(const char *str); static_rfstring & operator=(const static_rfstring & rhl); ~static_rfstring(); private: class stringvalue { public: stringvalue(const char *str); ~stringvalue(); char *value; int rfcount; }; stringvalue *strvalue; static list<stringvalue *> strvaluelist; }; // static_rfstring.cpp #include "static_rfstring.h" std::list<static_rfstring::stringvalue *> static_rfstring::strvaluelist; static_rfstring::static_rfstring(const char *str) { // 查找字符串是否已经存在 for (std::list<static_rfstring::stringvalue *>::iterator it = strvaluelist.begin();it != strvaluelist.end();++it) { if ((strlen((*it)->value) == strlen(str)) && (0 == strcmp(str, (*it)->value))) { (*it)->rfcount++; strvalue = *it; return; } } // 不存在则新构建个stringvalue对象 strvalue = new stringvalue(str); strvaluelist.push_back(strvalue); } static_rfstring::static_rfstring(const static_rfstring & rhl) { strvalue = rhl.strvalue; strvalue->rfcount++; } static_rfstring & static_rfstring::operator=(const char *str) { if (--strvalue->rfcount == 0) { delete strvalue; } for (std::list<static_rfstring::stringvalue *>::iterator it = strvaluelist.begin(); it != strvaluelist.end(); ++it) { if ((strlen((*it)->value) == strlen(str)) && (0 == strcmp(str, (*it)->value))) { (*it)->rfcount++; strvalue = *it; return *this; } } // 新构建一个stringvalue对象 strvalue = new stringvalue(str); strvaluelist.push_back(strvalue); return *this; } static_rfstring & static_rfstring::operator=(const static_rfstring & rhl) { if (this == &rhl) { return *this; } if (--strvalue->rfcount == 0) { delete strvalue; } strvalue = rhl.strvalue; strvalue->rfcount++; return *this; } static_rfstring::~static_rfstring() { for (std::list<static_rfstring::stringvalue *>::iterator it = strvaluelist.begin(); it != strvaluelist.end(); ++it) { if ((*it) == strvalue) { if (--(*it)->rfcount == 0) { strvaluelist.remove(strvalue); delete strvalue; } return; } } } static_rfstring::stringvalue::stringvalue(const char *str):rfcount(1) { value = new char[strlen(str) + 1]; strcpy(value, str); } static_rfstring::stringvalue::~stringvalue() { delete value; value = nullptr; }