Static成員變量的使用

#include <iostream> using namespace std; class enemytarget { public: enemytarget() { ++numtargets; } enemytarget(const enemytarget&) { ++numtargets; } ~enemytarget() { --numtargets; } static size_t numberoftargets() { return numtargets; } private: static size_t numtargets; }; int main() { enemytarget obj; obj.numberoftargets(); }

 

訪問錯誤，因爲 numtargets沒有內存空間所以鏈接出錯，

 

#include <iostream> using namespace std; class enemytarget { public: enemytarget() { ++numtargets; } enemytarget(const enemytarget&) { ++numtargets; } ~enemytarget() { --numtargets; } static size_t numberoftargets() { return numtargets; } private: static size_t numtargets; }; size_t enemytarget::numtargets = 0; int main() { enemytarget obj; obj.numberoftargets(); }

 

這個訪問正確，因爲numtargets有內存空間，

size_t enemytarget::numtargets = 0;  給numtargets 申請內存空間