How to determine if compiling for 64-bit iOS in Xcode

问题:

Consider the following function

CGSize CGSizeIntegral(CGSize size) {     return CGSizeMake(ceilf(size.width), ceilf(size.height)); } 

CGSize actually consists of two CGFloats, and CGFloat's definition changes depending on the architecture:

typedef float CGFloat;// 32-bit typedef double CGFloat;// 64-bit 

So, the above code is wrong on 64-bit systems, and needs to be updated with something like

CGSize CGSizeIntegral(CGSize size) { #if 64_bit     return CGSizeMake(ceil(size.width), ceil(size.height)); #else     return CGSizeMake(ceilf(size.width), ceilf(size.height)); #endif } 

There is surely a compiler macro/constant for this (for Mac we can use INTEL_X86 for example) but I haven't been able to find this in the 64-bit transition guide.

How can I determine what architecture is being built for?

回答1:

To determine if you are compiling for 64-bit, use __LP64__:

#if __LP64__     return CGSizeMake(ceil(size.width), ceil(size.height)); #else     return CGSizeMake(ceilf(size.width), ceilf(size.height)); #endif 

__LP64__ stands for "longs and pointers are 64-bit" and is architecture-neutral.

According to your transition guide it applies for iOS as well:

The compiler defines the __LP64__ macro when compiling for the 64-bit runtime.

However, the preferred way to handle your use case is to use CGFLOAT_IS_DOUBLE. There is no guarantee that __LP64__ will always mean the CGFloat is a double, but it would be guaranteed with CGFLOAT_IS_DOUBLE.

#if CGFLOAT_IS_DOUBLE     return CGSizeMake(ceil(size.width), ceil(size.height)); #else     return CGSizeMake(ceilf(size.width), ceilf(size.height)); #endif 

回答2:

For Swift, and neglecting the OP's specific question involving CGFloats, etc., the following may be more swiftish:

  #if (arch(i386) || arch(arm))      ....  // For 32-bit systems   #else      ....  // For 64-bit systems   #endif     #if (arch(x86_64) || arch(arm64))      ....  // For 64-bit systems   #endif 

On the other hand, the compile-time constants discussed in the above answer are also available in Swift, if they are preferred.

This is mostly copied from here: https://stackoverflow.com/a/24869607/253938

And the Apple docs about these Swift compile-time constants is here: https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithCAPIs.html (at the very bottom of the page).

文章来源: How to determine if compiling for 64-bit iOS in Xcode