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Adding Last Build Date & Time

If you need or want the date and/or time the last time your app was built then there are two handy macros you can use. Consider the following example:

char *date = __DATE__;  // e.g. 'Dec 15 2009'
char *time = __TIME__;  // e.g. '15:25:56'
NSLog(@"Build date: %s", date);
NSLog(@"Build time: %s", time);

I tested it with GCC 4.0, GCC 4.2 and even the new LLVM GCC 4.2. It worked fine with all three compilers.

Those are precompiler macros which work by getting the precompiler to replace them with the current date and time when the file in which they are located in gets built. Bear in mind that generally building is incremental and therefore these will only get updated if there really IS a new build happening. That’s a drawback if you forget it, but you can or should always do a build – clean before you build a release or distribution version to make certain all got updated.

Since those macros date back to C times they get replaced with C-style strings. That’s a pointer to a char array with a binary zero at the end to terminate the string. To convert them to obj-C NSStrings is simple by means of the %s formatter or by using one of the more complicated initializers of NSString.

char *date = __DATE__;
char *time = __TIME__;
NSString *myDate = [NSString stringWithCString:date encoding:NSASCIIStringEncoding];
NSString *myTime = [NSString stringWithFormat:@"%s", time];

Finally if you are really so much “pro” that the build time of your app matters, then you will probably also ask if there is a way to force building of certain files to forego the incremental building. Sure you can. All you need to do is to add an extra script to your target to set the last modified time of the file using these macros to the future.

touch -t 2012310000 "${PROJECT_DIR}/Classes/CalendarAppDelegate.m"

Touching Script

It’s not enough to simply set the modified time once because then the next modification sets it back to the current date. Thus the need for this simple unobtrusive script, in this example I am setting the modified time for CalendarAppDelegate.m to Dec 31st 2020 which is sufficiently far away so that this blog article will work for the next 11 years. :-)

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