Compile Error with: switch, “expected expression before”

问题

Cut to the chase I have recreated my problem as it is fairly self explanatory.

this complies without error:

switch (n) {
    case 1:
        NSLog(@"");
        NSString *aStr;
        break;
    default:
        break;
    }

this compiles with error and it's only missing the NSLog():

switch (n) {
    case 1:
        NSString *aStr;
        break;
    default:
        break;
    }

it throws an error at compile "Expected expression before 'NSString'"

Am I missing something here?

回答1:

In normal C you'd have to enclose this in brackets in both cases. I suspect this may fix your problem:

case 1:
{
    NSLog(@"");
    NSString *aStr;
    break;
}

See this SO question for more info.

Another way to get around this problem is to put a statement between the case label and the first declaration as you've done in your working example above. See the comments and Quinn Taylor's answer for more info.

回答2:

You can't declare a variable as the first statement in a case without brackets, and in many other contexts in C-based languages. See Declaring variables inside a switch statement for details.

回答3:

case 0: {
    Loading my nib file;
    break; 
}
case 1: {
    Loading another nib file;
    break; 
}
Note that if you don't have an assignment (x = y) right after the case it won't be a problem. For example:

来源：https://stackoverflow.com/questions/2036819/compile-error-with-switch-expected-expression-before