在switch语句奇怪的变量范围 [英] odd variable scope in switch statement

问题描述

这个问题让我想起了一个古老的悬而未决的问题在我的脑海约开关：

This question reminded me of an old unanswered question in my mind about switch:

    int personType = 1;
    switch (personType)
    {
        case 1:
            Employee emp = new Employee();
            emp.ExperienceInfo();
            break;
        case 2:
            Employee emp = new Employee(); 
            //Error: A local variable named 'emp' is already defined in this scope
            emp.ManagementInfo();
            break;
        case 3:
            Student st = new Student();
            st.EducationInfo();
            break;
        default:
            MessageBox.Show("Not valid ...");
    }

为什么EMP在案例2的认可？在C ++（如果我没看错），我们可以使用多种情况在一起，但在C＃中这是不可能的，我们应该关闭案例1 与休息所以下面的代码似乎是正确的C ++和错误在C＃中：

why is emp recognized in 'case 2'? in C++ (if I am not wrong) we could use multiple cases together, but in C# that is impossible and we should close case 1 with break so the following code seems right in C++ and wrong in C#:

case 1:
case 2:
   SomeMethodUsedByBothStates();

当我们不能有这样的行为，所以我们为什么要能在<$ C $申报EMP C>案例1 ，看看它在 2的情况下？如果无法在两个个案，一起发生何必对象均可以看到？

When we can not have such behaviour so why should we be able to declare emp in case 1 and see it in case 2? If never two cases happen together so why should the object be seen in both?

推荐答案

情况下并不创建在C范围++或C＃。所有的情况下内声明的变量都在相同的范围，即switch语句。你需要，如果你想这些变量是本地的一些特定的情况下使用大括号：

Cases do not create scope in c++ or in c#. All of those variables declared inside a case are in the same scope, that of the switch statement. You need to use braces if you want those variables to be local to some specific case:

switch (personType)
{
    case 1: {
        Employee emp = new Employee();
        emp.ExperienceInfo();
        break;
    }
    case 2: {
        Employee emp = new Employee(); 
        // No longer an error; now 'emp' is local to this case.
        emp.ManagementInfo();
        break;
    }
    case 3: {
        Student st = new Student();
        st.EducationInfo();
        break;
    }
    ...
}

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