rule of three
rule of three or rule of five (額外多move). 此rule是根據rules of thumb in C++所產生 主要是為了預防再做資源管理時發生不可預期的錯誤, 所建議的撰寫規則. 如下為一個經由給定(=)後所產生的double free問題. #include <iostream> #include <string> class ResourceFreeFailed { private: char * m_str; public: ~ ResourceFreeFailed() { delete [] m_str; } ResourceFreeFailed() = default ; ResourceFreeFailed( const char * pstr) : m_str( new char [ 128 ]) { std :: strcpy(m_str, pstr); } }; int main () { ResourceFreeFailed c( "resource" ); { // d will release resource of c ResourceFreeFailed d; // ERROR: assign c to d d = c; } // c will release resource, but someting is wrong return 0 ; } [1][2]定義了兩種情況,在撰寫class時候需要記得此規則: 撰寫的class有需要自己做資源管理(resource management) 當撰寫以下其中一個成員函數時,需要一併明確定義其他成員函數 destructor copy constructor copy assignment operator move constructor (C+