\u4e0b\u9762\u6211\u4eec\u5c06\u9010\u6b65\u5b9e\u73b0\u5e76\u5b8c\u5584\u8fd9\u4e2a\u901a\u7528\u7684\u8ba1\u6570\u7c7b\u3002<\/p>\n
class Counter { public: Counter() { ++count; } Counter(const Counter&) { ++count; } ~Counter() { --count; } static size_t howMany() { return count; } private: static size_t count; }; \/\/ This still goes in an implementation file size_t Counter::count = 0;<\/pre>\n\u4e0a\u9762\u8fd9\u4e2aCounter\u7c7b\u80fd\u5426\u6b63\u786e\u5b8c\u6210\u8ba1\u6570\u5462\uff1f\u4f8b\u5982\uff1aWidget\u7c7b\u5229\u7528\u5b83\u6765\u8fdb\u884c\u5b9e\u4f8b\u8ba1\u6570\uff1a<\/p>\n
\/\/ embed a Counter to count objects class Widget { public: ..... \/\/ all the usual public \/\/ Widget stuff static size_t howMany() { return Counter::howMany(); } private: ..... \/\/ all the usual private \/\/ Widget stuff Counter c; }; \/\/or: \/\/ inherit from Counter to count objects class Widget: public Counter { ..... \/\/ all the usual public \/\/ Widget stuff private: ..... \/\/ all the usual private \/\/ Widget stuff };<\/pre>\n\u5bf9\u4e8eWidget\u672c\u8eab\u6765\u8bf4\uff0cCounter\u5b8c\u6210\u4e86\u4efb\u52a1\u3002\u7136\u800c\uff0c\u5982\u679c\u6211\u4eec\u5728\u540c\u4e00\u8fdb\u7a0b\u4e2d\u8fd8\u9700\u8981\u5229\u7528Counter\u6765\u8ba1\u6570Fish\u7c7b\uff0c\u663e\u7136\uff0cCounter\u5c31\u4e0d\u80fd\u80dc\u4efb\uff0c\u56e0\u4e3a\u5b83\u53ea\u6709\u4e00\u4e2a\u9759\u6001\u6210\u5458\u53d8\u91cf\uff0c\u5b83\u4f1a\u5c06Widget\u548cFish\u7684\u4e2a\u6570\u4e00\u8d77\u7edf\u8ba1\u3002\u8fd9\u4e2a\u65b9\u6848\u4e0d\u884c\uff0c\u600e\u4e48\u529e\uff1f\u7528\u6a21\u677f\uff01\u5982\u4e0b\uff1a<\/p>\n
template<typename T> class Counter { public: Counter() { ++count; } Counter(const Counter&) { ++count; } ~Counter() { --count; } static size_t howMany() { return count; } private: static size_t count; }; \/\/ this now can go in header template<typename T> size_t Counter<T>::count = 0;<\/pre>\n\u5219\u4e0a\u9762\u7684\u5b9e\u73b0\u53d8\u6210\uff1a<\/p>\n
\/\/ embed a Counter to count objects class Widget { public: ..... static size_t howMany() {return Counter<Widget>::howMany();} private: ..... Counter<Widget> c; }; \/\/or: \/\/ inherit from Counter to count objects class Widget: public Counter<Widget> { ..... };<\/pre>\n\u8fd9\u6837\uff0c\u5176\u4ed6\u7c7b\u5c31\u53ef\u4ee5\u4f7f\u7528Counter\u8ba1\u6570\u81ea\u5df1\u7684\u5b9e\u4f8b\u4e86\uff0c\u5b83\u4eec\u5c06\u4e92\u4e0d\u5f71\u54cd\u3002
\n\u4e0a\u9762\u4e24\u79cd\u65b9\u6848\u90fd\u53ef\u6b63\u786e\u5b9e\u73b0\u8ba1\u6570\uff0c\u6211\u4eec\u7ee7\u7eed\u63a2\u8ba8\u8fd9\u4e24\u79cd\u65b9\u6848\u7684\u4f18\u7f3a\u70b9\u3002
\n\u9996\u5148\u8bb2public\u7ee7\u627f\uff0c\u5373class Widget: public Counter<Widget>\u8fd9\u79cd\u65b9\u6848\uff1a\u6709\u7ecf\u9a8c\u7684\u8bfb\u8005\u80af\u5b9a\u4f1a\u60f3\u5230\u57fa\u7c7bCounter\u7684\u6790\u6784\u51fd\u6570\u8981\u53d8\u4e3a\u865a\u51fd\u6570\u3002\u5426\u5219\u901a\u8fc7\u57fa\u7c7b\u6307\u9488delete\u6d3e\u751f\u7c7b\u65f6\uff0c\u7ed3\u679c\u672a\u5b9a\u4e49\uff08\u53ef\u80fd\u5bfc\u81f4\u7a0b\u5e8fcrash\u6216\u5176\u4ed6\uff09<\/p>\n
Counter<Widget> *pw = new Widget; \/\/ get base class ptr to derived class object ...... delete pw; \/\/ yields undefined results if the base class lacks a virtual destructor<\/pre>\n\u4f46\u4e00\u65e6Counter\u6709\u865a\u6790\u6784\u51fd\u6570\uff0c\u5c31\u4f1a\u7ed9\u7c7b\u5e26\u5165vTable\uff0c\u591a\u5360\u7528\u4e86\u7a7a\u95f4\u5e76\u5f71\u54cd\u5ba2\u6237\u7c7b\u7684\u6548\u7387\u3002<\/b>\u89e3\u51b3\u65b9\u6cd5\u53ef\u4ee5\u662f\u5c06\u6790\u6784\u51fd\u6570\u4f5c\u4e3aprotected\u6210\u5458\u3002\u8fd9\u6837\u5c31\u4e0d\u80fddelete pw\uff0c\u56e0\u4e3a\u5b83\u4f1a\u5bfc\u81f4\u7f16\u8bd1\u9519\u8bef\u3002<\/p>\ntemplate<typename T> class Counter { public: ..... protected: ~Counter() { --count; } ..... };<\/pre>\n\u5176\u6b21\uff0cCounter\u4f5c\u4e3a\u5ba2\u6237\u7c7b\u7684\u6210\u5458\u53d8\u91cf\u8fd9\u79cd\u65b9\u6848\uff08\u8fd9\u65f6Counter\u7684\u6790\u6784\u51fd\u6570\u5fc5\u987bpublic\uff09\u3002\u4e00\u4e2a\u660e\u663e\u7684\u7f3a\u70b9\u662f\u5ba2\u6237\u7c7b\u5fc5\u987b\u5b9a\u4e49Counter\u4e3a\u5176\u6210\u5458\u53d8\u91cf\u540c\u65f6\u8fd8\u5f97\u5b9a\u4e49\u4e00\u4e2ainline\u51fd\u6570\u4ee5\u8c03\u7528Counter\u7c7b\u5f97HowMany\u51fd\u6570\u3002\u53e6\u4e00\u4e2a\u8f83\u9690\u853d\u7684\u7f3a\u70b9\uff1a\u5b83\u589e\u5927\u4e86\u5ba2\u6237\u7c7b\u6240\u5360\u7528\u7684\u5185\u5b58\u3002Counter\u7c7b\u6ca1\u6709\u975e\u9759\u6001\u6210\u5458\u53d8\u91cf\uff0c\u6709\u4eba\u5c31\u53ef\u80fd\u4f1a\u8ba4\u4e3aCounter\u5bf9\u8c61\u7684\u5927\u5c0f\u4e3a0\uff0c\u5176\u5b9e\u4e0d\u7136\uff0cC++\u89c4\u5b9a\u6240\u6709\u5bf9\u8c61\u7684\u5927\u5c0f\u6700\u5c0f\u5fc5\u987b\u4e3a1\u5b57\u8282<\/b>\u3002\u6240\u4ee5\u8fd9\u7528\u65b9\u6848\u589e\u52a0\u4e86\u5ba2\u6237\u7c7b\u7684\u5927\u5c0f\u3002\u4f7f\u7528\u6d3e\u751f\u5219\u4e0d\u4e00\u6837\uff0c\u57fa\u7c7bsize\u53ef\u4ee50<\/b>\uff0c\u6240\u4ee5public\u7ee7\u627f\u65b9\u6848\u4e0d\u4f1a\u589e\u52a0\u5ba2\u6237\u7c7b\u7684\u5927\u5c0f\u3002<\/p>\n