c++ - 无法在初始化列表中捕获

Question

对于以下代码:

#include <iostream>

struct Str
{
    Str() { throw 100; }
};

class Cla
{
public:
    Cla()
    try : m_mem() { }
    catch(...)
    {
        std::cout << "Catch block is called"<< std::endl;
    }
private:
    Str m_mem;
};

int main()
{
    Cla obj;
}

我试图在 catch 块中捕获异常。但是catch块运行后，系统仍然调用std::terminate来终止程序。我没有在catch块中重新抛出异常，你能告诉我系统崩溃的原因吗？谢谢!
这是在编译器资源管理器上的测试: https://godbolt.org/z/74sTcxrY4

Answer 1

你在自相矛盾。

I tried to catch the exception in the catch block. But after the catch block is run

如果运行 catch 块，您就成功地从初始化列表中捕获了异常。你只是对接下来发生的事情感到惊讶。
首先，让我们想想当构造函数抛出时会发生什么:对象没有被构造。对？构造函数从未完成设置，因此您不能将其用于任何事情。

int main() {
   Cla obj;     // member subobject constructor throw, but we caught it!
   obj.print(); // but we still can't use this here, because the constructor never completed
}

因此，让您在这里吞下异常并没有真正意义。您无法处理它，因为您无法返回并重新尝试构造您的成员和基类子对象。如果您没有正确构造的对象，C++ 处理它的唯一方法是展开块作用域，否则该对象将被假定为……嗯，一个真实的对象。
因此，根据 documentation :

Every catch-clause in the function-try-block for a constructor must terminate by throwing an exception. If the control reaches the end of such handler, the current exception is automatically rethrown as if by throw;. The return statement is not allowed in any catch clause of a constructor's function-try-block.

... 等价于标准 ( draft )

The currently handled exception is rethrown if control reaches the end of a handler of the function-try-block of a constructor or destructor.Otherwise, flowing off the end of the compound-statement of a handler of a function-try-block is equivalent to flowing off the end of the compound-statement of that function (see [stmt.return])