macOS Help with attributesOfItemAtPath

[EggWhite]

I got a function online that takes and NSString of a path and returns the inode value. But when I pass it a string it always errors with the following
Program received signal: “EXC_BAD_ACCESS”.

Here are the two strings I have tried, do I need to put then in some sort of special format.
NSString * temp = @"/Users/username/Desktop/Dropbox/Deleted/KeePass/KeePass.exe";
NSString *temp =@"/System/Library/Fonts/AppleGothic.ttf";

long getInode(NSString* path) {
	NSFileManager* fm = [NSFileManager defaultManager];
	NSError* error;
	NSDictionary* info = [fm attributesOfItemAtPath:path error:&error];
	NSNumber* inode = [info objectForKey:NSFileSystemFileNumber];
	if (error) {
		[NSApp presentError:error];
	}	
	return [inode longValue];
}

 

[lee1210]

What line does the code die on?

-Lee

 

[EggWhite]

Sorry should have been more clear. The code doesn't die, but the following prints "Program received signal: “EXC_BAD_ACCESS”." to the console


if (error) {
[NSApp presentError:error];
}

 

[lee1210]

I don't think that's the result you'd get from that line. That looks like a signal from the system. If you're running in XCode you get a backtrace by entering bt at the gdb prompt when execution stops.

-Lee

 

[Sydde]

I would guess that what is happening is the NSNumber is not being returned because the dictionary may not have that key. Add a check to see if you have a non-nil value for inode.

 

[EggWhite]

I stepped through the code line by line and it does seem to die now on "[NSApp presentError:error]; ", which I added when I was debuging to see why I wasn't getting the correct result.

I think my issue is because I didn't initialize *error to nil then it was always entering the if(error) check and I am getting the bad access error since that pointer value is no good. Does that make sense?

Sorry for the dumb questions this is my first OSX app, and I only started with iPhone programing less then a year ago so I am still learning.

 

[kpua]

Your suspicion about not initializing the error pointer is correct. It's a random value, so unless you get lucky, the 'if (error)' branch is taken, and a bogus pointer is passed to -[NSApp presentError:], causing a crash when it is later dereferenced.

 

[gnasher729]

Read the documentation of attributesOfItemAtPath. error is _only_ set if an error occurs. So what does error contain if there was no error?

 

[lee1210]

Read the documentation of attributesOfItemAtPath. error is _only_ set if an error occurs. So what does error contain if there was no error?

The sound of a tree falling when no one is around to hear it?

-Lee

 

[kpua]

It contains whatever it contained before the call. In this case, it contains random unpredictable garbage, whatever was left on the stack when the method was called.

(Nice one lee )

 

[EggWhite]

Thanks for all the help with this issue. Everything seems to be working fine now.