@try - catch block in Objective-C

Question

Why doesn't @try block work? It crashed the app, but it was supposed to be caught by the @try block.

 NSString* test = [NSString stringWithString:@"ss"];

 @try {
    [test characterAtIndex:6];

 }
 @catch (NSException * e) {
    NSLog(@"Exception: %@", e);
 }
 @finally {
    NSLog(@"finally");
 }

You can replace NSString* test = [NSString stringWithString:@"ss"]; with NSString* test = @"ss"; — Duyen-Hoa, Jul 16 '14 at 12:21
Are you sure it is not something else because the exact code you have pasted above works fine. 2010-07-29 16:45:57.677 test[93103:207] Exception: *** -[NSCFString characterAtIndex:]: Range or index out of bounds 2010-07-29 16:45:57.678 test[93103:207] finally — mbogh, Jul 29 '10 at 14:47

score 148 · Answer 1 · edited Jun 20 '20 at 09:12

148

All work perfectly :)

 NSString *test = @"test";
 unichar a;
 int index = 5;
    
 @try {
    a = [test characterAtIndex:index];
 }
 @catch (NSException *exception) {
    NSLog(@"%@", exception.reason);
    NSLog(@"Char at index %d cannot be found", index);
    NSLog(@"Max index is: %lu", [test length] - 1);
 }
 @finally {
    NSLog(@"Finally condition");
 }

Log:

[__NSCFConstantString characterAtIndex:]: Range or index out of bounds

Char at index 5 cannot be found

Max index is: 3

Finally condition

edited Jun 20 '20 at 09:12

Community

1
1

answered Nov 29 '12 at 02:23

iTux

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Correct but a bit misleading - remember that the @finally block gets executed in BOTH cases, i.e. regardless of whether exception was or was not thrown. – Lenka Pitonakova Jun 20 '17 at 17:16
Yeah, I miss this :) – iTux Jun 20 '17 at 18:41
Please fix as @Elendurwen noted. – Sanich Nov 14 '18 at 14:08

score 79 · Accepted Answer · edited Oct 31 '13 at 15:55

79

Now I've found the problem.

Removing the obj_exception_throw from my breakpoints solved this. Now it's caught by the @try block and also, NSSetUncaughtExceptionHandler will handle this if a @try block is missing.

edited Oct 31 '13 at 15:55

rob mayoff

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answered Jul 30 '10 at 08:47

Alexandru Circus

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IF you hit continue when the debugger breaks, you should see the exception gets thrown and caught by your handler. – JeremyP Jul 30 '10 at 12:17

score 0 · Answer 3 · answered Nov 15 '18 at 15:35

0

Objective-C is not Java. In Objective-C exceptions are what they are called. Exceptions! Don’t use them for error handling. It’s not their proposal. Just check the length of the string before using characterAtIndex and everything is fine....

answered Nov 15 '18 at 15:35

Thallius

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Using try-catch in Objective-C is generally not recommended because it can potentially mess up the ARC. – slow Feb 12 '19 at 18:26

@try - catch block in Objective-C

3 Answers3

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