For unknown reasons, I tried:

usleep(1,000,000); (hey, it was early, don’t laugh)

and it compiled. And usleep was even returning 0 as if it was working. Well, from what I can tell, usleep was only seeing 1. Not sure where the rest of the 0’s went. As I’m sure you know, that needs to be:

usleep(1000000);

My question is why doesn’t the compiler whine about me sending 3 arguments to a C function that only takes 1? I don’t even see a warning. I dug a little deeper. Turns if you want to see the error, you have to #include<unistd.h> (that’s where usleep’s prototype is declared). So why does this even compile? Shouldn’t the compiler want a declaration for usleep before I can use it? Thinking this might be some Xcode magic (hey, I don’t know), I created a very small test program and compiled it with gcc-3.3 on a NetBSD box. The results were the same. The next question was, what if I try call an undefined function? Enter, “tonyrndl(5);”. The file compiles just fine, but it doesn’t link. This is surprising to me. I guess I’ve been living in a world with -Wall on for too long and taken a lot of warnings for granted. Compiling again with -Wall gives a nice:

test.c:6: warning: implicit declaration of function `usleep'
test.c:7: warning: implicit declaration of function `tonyrndl'

So the only reason it compiled and linked with usleep is because usleep is in libc so the linker happily found it’s way home.

Thoughts about warnings

I am a fan of warnings. I just set -Wall -Werror in my current Xcode project and it already found a stupid typo. I was calling ‘NSlog’ somewhere where I needed ‘NSLog’ (why that links, I’m not sure). Those are the types of errors that should be caught before you even run your app. Xcode’s default $(WARNING_CFLAGS) is pretty good, and sometimes -Wall -Werror makes you jump through hoops to get something you know is OK just to compile. So it’s a trade off that each project has to decide for itself. Personally, I need -Werror to force me to address each warning. It’s too easy to just ignore the “8 warnings” in the lower corner of Xcode. -Wall seems like a good idea, at least to start with. However, my project is still small, we’ll see how long -Wall -Werror holds.

Note, if you only wanted to catch the example I gave above without -Wall, add -Wimplicit-function-declaration to your projects “Other warning flags” build setting.

Not a problem in C++

Turns out C++ no longer allows implicit declarations. Attempting to explicitly set -Wimplicit-function-declaration for the C++ compiler gives you a compiler error stating it’s an invalid parameter for C++, but valid for C or Obj-C.

Sleep? Wuh?

You should be asking, “why is he calling usleep or any sleep related function at all”? Don’t worry, it was only to test how a thread acted if it slept for a little bit here and there. And yes, I know about NSThread’s:

+ (void)sleepUntilDate:(NSDate *)aDate

but again, this was just a quick and dirty test.

This entry was posted on Monday, December 19th, 2005 at 6:51 am and is filed under Code. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.