break and label, “The label MyLabel is missing”

问题:

I have a code like this:

if(condition1)
{
    break MyLabel;
}
while(true)
{
    //some code here
    MyLabel: if(condition2) break;
    //more code here
}

and I get this error:

The label MyLabel is missing.

What's wrong?

回答1:

You can only break to a label that is on a textually enclosing statement. In your example, the label is NOT on a statement that encloses the break statement.

(For what it is worth, even higher-level languages that support goto don't allow you to jump into the middle of a loop from the outside. I'm thinking of C ... and older languages like FORTRAN.)

Java allows you to break out, but breaking in is illegal ... and will get you arrested :-)

_{(Sorry, I couldn't resist it. For those who don't get the joke, a "break in" is when someone enters your house to steal stuff - see "break and enter" ... )}

回答2:

You can't use labels as goto in that general way.
Use labels if you want to goto a higher level of nested code.

for example

l1: while
 l2: while
  l3: while
   break l1
   l4: while