c++ - 查找初始化列表中的哪个成员抛出异常

Question

假设我有一个类(class)，里面有一些成员。我知道带有初始化列表的 try-catch block 的语法如下

template<int N>
struct Member
{
    Member()
    {
        std::cout << "Default constructor of Member " << N << std::endl;
    }
};

class A 
{
    Member<1> m1;
    Member<2> m2;
    // n members 
public:
A() try
    : m1()
    , m2()
    {
        // constructor implementation
    }
    catch (std::exception const & e)
    {
               // ... cleanup 
        throw; // and rethrow
    }
};

由于涉及初始化列表，我不能使用多个 try catch block 。 如何判断哪个成员初始化抛出了异常？

Answer 1

可以追溯初始化过程

class A 
{
    Member<1> m1;
    bool m1threw = true;
    Member<2> m2;
    bool m2threw = true;
    // n members 
public:
A() try
    : m1()
    , m1threw(false)
    , m2()
    , m2threw(false)
    {
        // constructor implementation
    }
    catch (std::exception const & e)
    {
               // ... cleanup 
        if (m1threw) {
            // 
        }
        else if (m2threw) {

        }
        throw; // and rethrow
    }
};

注意 类内初始化只在c++11有效。使您的示例更复杂的是成员变量是默认构造的。如果他们的构造函数接受了一个参数，这将是 construction tracker idiom 的完美匹配。

我为 Member 提供了一个非默认构造函数来展示construction tracer idiom的示例

template<int N>
struct Member
{
    Member(int some_arg) 
    {
        std::cout << "Non default constructor of Meber " << N << std::endl;
    }
};

class A 
{
    Member<1> m1;
    Member<2> m2;
   enum TrackerType { NONE, ONE, TWO };
public:
   A(TrackerType tracker = NONE)
   try    // A constructor try block.
     : m1((tracker = ONE, 1)) // Can throw std::exception
     , m2((tracker = TWO, 1)) // Can throw std::exception
     {
         //TODO:
     }
   catch (std::exception const & e)
     {
        if (tracker == ONE) {
           std::cout << "m1 threw: " << e.what() << std::endl;
        }
        else if (tracker == TWO) {
           std::cout << "m2 threw: " << e.what() << std::endl;
        }
        throw;
     }
};

基本上这不需要额外的成员来实现跟踪 as you can see并且可以用 11 之前的 c++ 编译