Vincent Gable

CFShow(coreFoundationThingy) will print out a description of coreFoundationThingy to the console. Output looks something like:

{value = w:1186.000000 h:687.000000 type = kAXValueCGSizeType}

If NSLog() is printing something out as an NSCFType, try CFShow().

There are lots of examples of people using text searching and regular expressions to find data in webpages. These examples are doing it wrong.

NSXMLDocument and an XPath query are your friends. They really make finding elements within a webpage, RSS feed or XML documents very easy.

– Matt Gallagher

I haven’t used XPath before, but after seeing Matt’s example code, I am convinced he’s right, because I’ve seen the other side of things. (I’ll let you in on a dirty little secret — right now the worst bit of the code-base I’m working on parses XML.)

    NSError *error;
    NSXMLDocument *document =
        [[NSXMLDocument alloc] initWithData:responseData options:NSXMLDocumentTidyHTML error:&error];
    [document autorelease];
    
    // Deliberately ignore the error: with most HTML it will be filled with
    // numerous ”tidy” warnings.
    
    NSXMLElement *rootNode = [document rootElement];
    
    NSString *xpathQueryString =
        @”//div[@id=’newtothestore’]/div[@class=’modulecontent’]/div[@class=’list_content’]/ul/li/a”;
    NSArray *newItemsNodes = [rootNode nodesForXPath:xpathQueryString error:&error];
    if (error)
    {
        [[NSAlert alertWithError:error] runModal];
        return;
    }
(I added [document autorelease]; to the above code, because you should always immediately balance an alloc/init with autorelease, outside of your own init methods.)

Or: How to Make NSLog() Useful With Your Objects

Say you have an archaically named NSArray that you want to inspect — it’s easy to do, since NSLog(@"The bestiary is %@", bestiary); prints out the array’s contents

2008-09-16 19:46:06.445 Tester[2678:10b] The bestiary is (
Cheetah,
Pumpa,
Jaguar,
Panther,
Tiger,
Leopard
)

But if you try to NSLog your own object, you get pretty useless output, like

myObject = <MyObject: 0×53f330>

Fortunately, it’s easy to fix! Just implement the method -(NSString*) description; and whatever it returns will be printed by NSLog and GDB (po object, will print object in GDB and the Xcode debugging console).

Here’s an (unfortunately complex) example,

- (NSString*) description;
{
  return [NSString stringWithFormat:@”<%@ %p> = {\n\tquestion=%@,\n\tanswer=%@,\n\tsource=%@\n}”, [self className], self, self.question, self.answer, self.source];
}

output:

myObject = <MyObject 0×53eed0> = {
  question=What is the Best Thing Ever Of All Times, Ever?,
  answer=The Internet!,
  source=http://www.cabel.name/2008/01/2007-cabel-yay-awards.html
}

Useful Formatters and such

These macros have made my debugging-life easer.

%p tells NSLog to print the address of a pointer.

-className returns gives the name of a class as an NSString.

Don’t manually print out a Cocoa struct, ever, there are already NSStringTo* functions to do that for you, like NSStringFromPoint().

NSStringFromSelector() works as advertized (and paired with NSSelectorFromString() is very useful in general).

%lld tells NSLog to print a long long (64-bit integer). See also, printf reference.

%Lf tells NSLog to print a long double. See also, printf reference.

Best Practices

Whenever you make a new object, I strongly recommended immediately implementing a description method, and religiously keeping it up to date (it’s not hard, honest!). This won’t fix bugs, but it will make finding some of them much easier.

Your code will also run faster because the internal implementation reduces message send overhead and increases pipelining potential.

–Matt Gallagher

I’ve written before about the advantages of a better enumeration paradigm, clearer code that’s faster to write, shorter, and with fewer bugs.

If you program in Cocoa, you should adopt fast enumeration post-haste.

Command + Option + Up-arrow will switch between a header and source-code file in Xcode. I wish I had figured this out years ago.

I have noticed a pattern in my Cocoa code, which I have been able to simplify. I often print out the value of a variable for debugging. 99 times out of 100, the code looks like this: NSLog(@"actionURL = %@", actionURL);, where actionURL is some variable.

But using the macros, I can say LOG_ID(actionURL);. This is shorter, and non-repetitive.

The macros I use to simplify debugging (2008-09-16):

#define FourCharCode2NSString(err) NSFileTypeForHFSTypeCode(err)

#define LOG_4CC(x) NSLog(@”%s = %@”, # x, FourCharCode2NSString(x))
#define LOG_FUNCTION() NSLog(@”%s”, __FUNCTION__)
#define LOG_ID(o) NSLog(@”%s = %@”, # o, o)
#define LOG_INT(i) NSLog(@”%s = %d”, # i, i)
#define LOG_INT64(ll) NSLog(@”%s = %lld”, # ll, ll)
#define LOG_FLOAT(f) NSLog(@”%s = %f”, # f, f)
#define LOG_LONG_FLOAT(f) NSLog(@”%s = %Lf”, # f, f)
#define LOG_OBJECT(o) LOG_ID(o)
#define LOG_POINT(p) NSLog(@”%s = %@”, # p, NSStringFromPoint(p))
#define LOG_RECT(r) NSLog(@”%s = %@”, # r, NSStringFromRect(r))
#define LOG_SIZE(s) NSLog(@”%s = %@”, # s, NSStringFromSize(s))

Look in assert.h for insight on how to roll your own debugging macros.

Your iSight camera can see into the IR spectrum. You can see the invisible IR light on your remote control if you watch it thought your iSight.

I have often recommended that people use file erasure tools regularly, especially when crossing international borders with their computers. Now we have one more reason to use them regularly: plausible deniability if you’re accused of erasing data to keep it from the police.

– Bruce Schneier

Finder -> Secure Empty Trash

/Developer/Applications/Utilities/CrashReporterPrefs.app can make crash reports much more useful.

Crash report-files are stored in ~/Library/Logs/CrashReporter/

Unfortunately, crash reports are not sent back to third-party developers, even when you send them to Apple.

Rands’ First Law of Information Management: “For each new piece of information you track, there is an equally old and useless piece of information you must throw away.”

–Rands in repose

So true.