Dan Wood: The Eponymous Weblog (Archives)

One thing that drives me crazy about debugging in XCode is how the default print-object command invokes debugDescription on an object. Normally this is the same as description, but for certain data objects, it's much less readable than plain old description. OK, it has a bit more information, but it's generally not what I'm looking for and it's formatted so poorly.

What I do in our application is to redefine debugDescription in terms of description for debug builds. (I bracket this code within and #ifdef so it's not built for the release version.) Here's NSDictionary:

@implementation NSDictionary ( OverrideDebug )

- (NSString *)debugDescription
{
    return [self description];
}

@end

I do something similar for NSSet.

Easy enough, right? For NSArray, I've gone a step further by only printing the first 20 or so items in the array. That way an array with thousands of items won't fill up my terminal!

@implementation NSArray ( OverrideDebug )

- (NSString *)debugDescription
{
    #define MAXARRAYSHOW 20
    if ([self count] > MAXARRAYSHOW)
    {
        NSArray *subArray = [self subarrayWithRange:
            NSMakeRange(0,MAXARRAYSHOW)];
        return [NSString stringWithFormat:@"%@ [... %d items]",
                    [subArray description], [self count]];
    }
    else
    {
        return [self description];
    }
}
@end

For NSDictionary, I've gone all out and made a much more useable description. This implementation shows the data in a nicely formatted Hex/ASCII dump that's much more scannable. I also cut it off at 1024 bytes since I don't really want to see much more than this, and I hate to have to wait for a megabyte-long chunk of data to finish displaying.

Note that I've also gone ahead and re-implemented description, not debugDescription, so I always get this new style of display.

@implementation NSData ( description )

- (NSString *)description
{
#define MAXDATABYTES 1024
    unsigned char *bytes = (unsigned char *)[self bytes];
    unsigned length = [self length];
    NSMutableString *buf = [NSMutableString stringWithFormat:
        @"NSData %d bytes:\n", length];
    int i, j;

    for ( i = 0 ; i < length ; i += 16 )
    {
        if (i > MAXDATABYTES)       // don't print too much!
        {
            [buf appendString:@"\n...\n"];
            break;
        }
        for ( j = 0 ; j < 16 ; j++ )    // Show the row in Hex
        {
            int offset = i+j;
            if (offset < length)
            {
                [buf appendFormat:@"%02X ",bytes[offset]];
            }
            else
            {
                [buf appendFormat:@"   "];
            }
        }
        [buf appendString:@"| "];   // now show in ASCII
        for ( j = 0 ; j < 16 ; j++ )
        {
            int offset = i+j;
            if (offset < length)
            {
                unsigned char theChar = bytes[offset];
                if (theChar < 32 || theChar > 127)
                {
                    theChar ='.';
                }
                [buf appendFormat:@"%c", theChar];
            }
        }
        [buf appendString:@"\n"];
    }
    [buf deleteCharactersInRange:NSMakeRange([buf length]-1, 1)];
    return buf;
}
@end

Can anybody think of more improvements to the standard ways out describing objects?