switch里面报crosses-initialization

如下写法会报错crosses initialization of ‘int r’

    switch(i) {
        case 1:
            int r = 1; // Failed to Compile
            cout << r;
            break;
        case 2:
            cout << r;
            break;
    };

正确的写法应该是

switch(i)
{
case 1:
    {
        int r = 1;
        cout << r;
    }
    break;
case 2:
    {
        int r = x - y;
        cout << r;
    }
    break;
};

标准说明如下：

It is possible to transfer into a block, but not in a way that
bypasses declarations with initialization. A program that jumps from a
point where a local variable with automatic storage duration is not in
scope to a point where it is in scope is ill-formed unless the
variable has POD type (3.9) and is declared without an initializer
(8.5).

https://stackoverflow.com/questions/2392655/what-are-the-signs-of-crosses-initialization