C++ – Why can’t variables be declared in a switch statement

cswitch statement

I've always wondered this – why can't you declare variables after a case label in a switch statement? In C++ you can declare variables pretty much anywhere (and declaring them close to first use is obviously a good thing) but the following still won't work:

switch (val)  
{  
case VAL:  
  // This won't work
  int newVal = 42;  
  break;
case ANOTHER_VAL:  
  ...
  break;
}

The above gives me the following error (MSC):

initialization of 'newVal' is skipped by 'case' label

This seems to be a limitation in other languages too. Why is this such a problem?

Best Answer

Case statements are only labels. This means the compiler will interpret this as a jump directly to the label. In C++, the problem here is one of scope. Your curly brackets define the scope as everything inside the switch statement. This means that you are left with a scope where a jump will be performed further into the code skipping the initialization.

The correct way to handle this is to define a scope specific to that case statement and define your variable within it:

switch (val)
{   
case VAL:  
{
  // This will work
  int newVal = 42;  
  break;
}
case ANOTHER_VAL:  
...
break;
}
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