{"id":129,"date":"2008-09-16T19:50:33","date_gmt":"2008-09-17T00:50:33","guid":{"rendered":"http:\/\/vgable.com\/blog\/2008\/09\/16\/description-little-known-hero-of-debugging\/"},"modified":"2008-09-16T19:50:36","modified_gmt":"2008-09-17T00:50:36","slug":"description-little-known-hero-of-debugging","status":"publish","type":"post","link":"https:\/\/vgable.com\/blog\/2008\/09\/16\/description-little-known-hero-of-debugging\/","title":{"rendered":"-description, Little-Known Hero of Debugging"},"content":{"rendered":"

Or: How to Make NSLog()<\/code> Useful With Your Objects<\/strong><\/p>\n

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

2008-09-16 19:46:06.445 Tester[2678:10b] The bestiary is (
\n Cheetah,
\n Pumpa,
\n Jaguar,
\n Panther,
\n Tiger,
\n Leopard
\n)\n<\/p><\/blockquote>\n

But if you try to NSLog<\/code> your own object, you get pretty useless output, like <\/p>\n

myObject = <MyObject: 0x53f330><\/p><\/blockquote>\n

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

Here’s an (unfortunately complex) example,
\n
- (NSString*) description;
\n{
\n  return [NSString stringWithFormat:@\"<%@ %p> = {\\n\\tquestion=%@,\\n\\tanswer=%@,\\n\\tsource=%@\\n}\", [self className], self, self.question, self.answer, self.source];
\n}
<\/code>
\noutput:<\/p>\n

myObject = <MyObject 0x53eed0> = {
\n  question=What is the Best Thing Ever Of All Times, Ever?,
\n  answer=The Internet!,
\n  source=http:\/\/www.cabel.name\/2008\/01\/2007-cabel-yay-awards.html
\n}<\/p><\/blockquote>\n

Useful Formatters and such<\/strong><\/p>\n

These macros have made my debugging-life easer<\/a>.<\/p>\n

%p<\/code> tells NSLog<\/code> to print the address of a pointer.<\/p>\n

-className<\/code> returns gives the name of a class as an NSString<\/code>.<\/p>\n

Don’t manually print out a Cocoa struct<\/code>, ever<\/em>, there are already NSStringTo*<\/code> functions to do that for you, like NSStringFromPoint()<\/code>.<\/p>\n

NSStringFromSelector()<\/code> works as advertized (and paired with NSSelectorFromString()<\/code> is very useful in general).<\/p>\n

%lld<\/code> tells NSLog<\/code> to print a long long<\/code> (64-bit integer). See also, printf<\/code> reference<\/a>.<\/p>\n

%Lf<\/code> tells NSLog<\/code> to print a long double<\/code>. See also, printf<\/code> reference<\/a>.<\/p>\n

Best Practices<\/strong><\/p>\n

Whenever you make a new object, I strongly<\/em> recommended immediately implementing a description<\/code> 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<\/em>.<\/p>\n","protected":false},"excerpt":{"rendered":"

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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,3,5,4,13,10],"tags":[77,83,174,78],"class_list":["post-129","post","type-post","status-publish","format-standard","hentry","category-cocoa","category-macosx","category-objective-c","category-programming","category-sample-code","category-tips","tag-debugging","tag-nslog","tag-nsobject","tag-nsstring"],"_links":{"self":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts\/129","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/comments?post=129"}],"version-history":[{"count":0,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts\/129\/revisions"}],"wp:attachment":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/media?parent=129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/categories?post=129"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/tags?post=129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}