lemene

說明

類的構造函數拋出異常，不會調用該類的析構函數，資源的釋放原則是編譯器申請的編譯器負責，程序員申請的程序員負責。
在實驗代碼中，子類Except的構造函數拋出異常，則Base和mMember1的構造函數是編譯器調用，因此編譯器會調用它們的析構函數，而mMember2由程序員主動使用new生成，因此需要程序員主動使用delete。

解決方法：

1. 在構造函數中使用try...catch結構
2. 使用類包裝資源申請，如auto_ptr。

實驗代碼

/** 
 * @file constructor_exception.cpp
 * @brief 測試構造函數異常引起的行為
 * @copyright public domain
 */
#include <iostream>
#include <exception>
#include <memory>
class Base {
public:
Base() { std::cout << "Base()" << std::endl; }
virtual ~Base() { std::cout << "~Base()" << std::endl; }
};
class Member {
public:
Member(int id):mId(id) { std::cout << "Member():" << mId << std::endl; }
virtual ~Member() { std::cout << "~Member()" << mId << std::endl; }
protected:
int mId;
};
class Except : public Base {
public:
Except() : mMember1(1), mMember2(NULL) { 
std::cout << "Except() enter" << std::endl; 
mMember2 = new Member(2);
mMember3.reset(new Member(3));
throw std::exception();
std::cout << "Except() leave" << std::endl; 
}
virtual ~Except() { 
delete mMember2;
std::cout << "~Except()" << std::endl; 
}
protected:
Member mMember1;
Member *mMember2;
std::auto_ptr<Member> mMember3;
};
int main() {
try {
Except e;
} catch (std::exception& e) {
std::cout << e.what() << std::endl;
}
return 0;
}

運行及結果

$ g++ constructor_exception.cpp 
$ ./a.out 
Base()
Member():1
Except() enter
Member():2
Member():3
~Member()3
~Member()1
~Base()
std::exception