c++ - 大括号括起来的初始化列表

Question

假设我有一个类似于这个的对象:

struct MenuDef
{
    int titleResourceId;

    struct MenuItemDef {
        char*               name;
        int                 value;
        SomeFunctionPtr     someFactory;
    } menuItems[10];
};

初始化是这样的:

const MenuDef m = {
    1,
    {
        {
            "zero",
            0,
            (SomeFunctionPtr) & MenuButton::factory,
        },
        {
            "one",
            1,
            (SomeFunctionPtr) & MenuButton::factory,
        },
        {
            "two",
            2,
            (SomeFunctionPtr) & MenuButton::factory,
        },
    }
};

假设 m.menuItems[3].someFactory == 0 是否安全？

例如在这样的循环中:

for ( int i = 0; m.menuItems[i].someFactory != 0; ++i)

或者为了安全起见，我是否必须手动插入最后一个元素来标记数组结束？

...
        {
            "two",
            2,
            (SomeFunctionPtr) & MenuButton::factory,
        },
        {
            "",
            0,
            (SomeFunctionPtr) 0,
        },
...

Answer 1

根据 8.5.1/7，我相信它是安全的:

If there are fewer initializers in the list than there are members in the aggregate, then each member not explicitly initialized shall be value-initialized (8.5).

提醒一下:

To value-initialize an object of type T means:

• if T is a class type (clause 9) with a user-declared constructor (12.1), then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);
• if T is a non-union class type without a user-declared constructor, then every non-static data member and base-class component of T is value-initialized;
• if T is an array type, then each element is value-initialized;
• otherwise, the object is zero-initialized