我阅读了 Paul Deitel 的C++ How to Program 8th Edition 一书。在第 645 页有一个声明:
When an exception is thrown from the constructor for an object that's created in a new expression, the dynamically allocated memory for that object is released.
为了验证这个说法，我写了如下代码:
#include <iostream>
#include <exception>
#include <memory>
class A{
public:
A(){std::cout << "A is coming." << std::endl;}
~A(){std::cout << "A is leaving." << std::endl;}
};
class B
{
public:
B()
{
std::cout << "B is coming." << std::endl;
A b;
throw 3;
}
~B(){std::cout << "B is leaving." << std::endl;}
};
int main(void)
{
try
{
std::shared_ptr<B> pi(new B);
}
catch(...)
{
std::cout << "Exception handled!" << std::endl;
}
}
输出是:
B is coming.
A is coming.
A is leaving.
Exception handled!
这表明没有调用B的析构函数，这似乎与上面的说法冲突。
我的代码是否正确以验证声明？如果不是，我应该如何修改它？如果是，是否说明这个说法是错误的？
最佳答案
你混淆了两件事:
- 正在释放内存
- 被调用的析构函数
您已经证明后者不会发生，这是有道理的:您如何才能摧毁未正确构建的东西？请注意，成员变量将调用它们的析构函数，因为在构造函数抛出异常时所有成员变量都已完全构造。
但这与释放内存无关，肯定会发生。
[C++11: 15.2/2]:An object of any storage duration whose initialization or destruction is terminated by an exception will have destructors executed for all of its fully constructed subobjects (excluding the variant members of a union-like class), that is, for subobjects for which the principal constructor (12.6.2) has completed execution and the destructor has not yet begun execution. Similarly, if the non-delegating constructor for an object has completed execution and a delegating constructor for that object exits with an exception, the object’s destructor will be invoked. If the object was allocated in a new-expression, the matching deallocation function (3.7.4.2, 5.3.4, 12.5), if any, is called to free the storage occupied by the object.
关于c++ - 为什么从构造函数抛出异常时会发生内存泄漏？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30821651/