What definitions exist like __LP64__ and __arm64__ in Cocoa that differentiate platforms at compile time? Where or how are they defined?

user_184130 0
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With the introduction of arm64 as a standard architecture for the iphoneos platform it's necessary in some cases to implement compile-time conditions for code that is specific to the 64/32 architecture.

If you look at CoreGraphics/CGBase.h and how some popular open source projects are providing support for arm64 it's clear that you can check for the presence of the 64bit runtime like so:

#if defined(__LP64__) && __LP64__
...
#else
...
#endif

It's also possible to check specifically for arm64 (as opposed to just a 64bit runtime) as mentioned in this fix for erikdoe/ocmock

#ifdef __arm64__
...
#else
....
#endif

Is there a comprehensive list, or documentation for these kinds of definitions? Where or how are they defined?

clang 64-bit objective-c c ios
3 Answers

After some years, I landed here while searching and offer this update:

Note that __LP64__ is not a reliable check for the 64-bit runtime on any system that doesn't define __LP64__. This is because LP64 is the name of the data model in use, which is one of several 64-bit data models that might be selected.

Data model is the term used to describe the arrangement of standard C/C++ types by size. In this example, LP64 means that long and pointer are 64-bits, with the implication that everything else is smaller. This is a fairly standard GCC/Clang configuration, but by no means universal (other 64-bit platforms use other standards). Microsoft, I believe, uses LLP64 as their data model, with long long and pointer being 64 bits, while int and long are both allocated 32.

There is even a SILP64 data model - 64-bit shorts, yikes!

If you want to detect 64-bits, you will do better to look at the predefined-macros page, which has been mentioned already. You can detect the architecture and go from there. If you want to know the size of certain types, you will probably be able to determine that information more portably by either (1) checking the result of sizeof(...); or (2) checking the values for e.g., INT_MAX, LONG_MAX, etc.

user_40290140
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