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News: Read this please.The Great Kangaroo Escape Looking for reviews of the 4th ed on Amazon!   Twitter:  @skochan

+ Official Forum for Programming in Objective-C (the iPhone Programming Language) - Stephen Kochan
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| | |-+ Chapter 12 - The Preprocessor
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Author Topic: P252 (Read 1335 times)
Posts: 14

on: April 17, 2011, 11:29:21 AM

"As an example of how this can be used, the following lines appear in the Foundation header file NSString.h:
 #define NSMaximumStringLength   (INT_MAX-1)

This tests the value of the defined variable MAC_OS_X_VERSION_MIN_REQUIRED against the defined variable MAC_OS_X_VERSION_10_5. If the former is less than the latter, the #define that follows is processed; otherwise, it is skipped. "

I am reading Chapter 12 The Preprocessor today, and this sentence confuses me.
from the name  MAC_OS_X_VERSION_MIN_REQUIRED, it seems like it is defined name using the #define statement, but since a defined name is not a variable, as it's mentioned previously.

can someone tell me what kind data type it is?
Hero Member
Posts: 3114

Reply #1 on: September 09, 2011, 03:03:20 PM

They are defined names and their values get substituted and then compared by the #if, which can evaluate numeric expressions.  So there's a double processing (in a sense) of that line that's done by the preprocessor:  first substitute the text defined for the two name, then evaluate the expression. 


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