Invalid token at start of a preprocessor expression Xcode

Question

#define A7VERSION() ({[[[[[UIDevice currentDevice] systemVersion] componentsSeparatedByString:@"."] objectAtIndex:0] intValue];})

#define IS_OS_7 A7VERSION()>=7

The above declaration seems to compile well.

But as soon as I add it a .m file I get the following exception "invalid token at start of a preprocessor expression". I am not able to understand where I could be wrong

@implementation AppViewController
#if IS_OS_7
….
#else
….  
#endif
@end

Due to the dynamic nature of Objective-C, the value of method calls cannot be determined at compile time, meaning that a runtime check is all that you can do. A good list of runtime checks is here: http://stackoverflow.com/questions/3339722/check-iphone-ios-version — CodaFi, Jul 05 '13 at 05:05
THIS IS NOT A DUPLICATE QUESTION. Its related to preprocessor . Nor does my question title specify its a version check code.I was expecting it to work at runtime which was wrong and corrected by @bbum — weber67, Jul 06 '13 at 06:21

score 10 · Accepted Answer · edited Mar 30 '16 at 18:54

10

The problem has nothing to do with iOS 7.

Your #define does not lead to something that can be resolved at compile time. An #ifdef only works if the conditional is something that can be determined at compile time. It cannot be used to change behavior at runtime based on the environment an app is running on.

edited Mar 30 '16 at 18:54

jscs

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answered Jul 05 '13 at 05:07

bbum

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its not #ifdef. it is #if condition – weber67 Jul 05 '13 at 05:23
@weber67 doesn't matter. It is still a compile time test that cannot generate dynamic behavior at runtime. – bbum Jul 05 '13 at 14:38

Invalid token at start of a preprocessor expression Xcode

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