Handling CGFloat with an NSScanner on arm64

问题:

Apparently CGFloat is double on arm64:

#if defined(__LP64__) && __LP64__
# define CGFLOAT_TYPE double
# define CGFLOAT_IS_DOUBLE 1
# define CGFLOAT_MIN DBL_MIN
# define CGFLOAT_MAX DBL_MAX
#else
# define CGFLOAT_TYPE float
# define CGFLOAT_IS_DOUBLE 0
# define CGFLOAT_MIN FLT_MIN
# define CGFLOAT_MAX FLT_MAX
#endif

So the code

NSScanner *scanner = [NSScanner scannerWithString:string];
CGFloat c[components];
[scanner scanFloat:&c[i]]

which was working fine for 32-bit apps, is broken for 64-bit. It can be replaced with

NSScanner *scanner = [NSScanner scannerWithString:string];
CGFloat c[components];
#if CGFLOAT_IS_DOUBLE 
   [scanner scanDouble:&c[i]]; 
#else 
   [scanner scanFloat:&c[i]]; 
#endif

But is there a better alternative?

回答1:

NSScanner only supports a few basic types, so you're going to need to have that #if directive somewhere. That said, if you're using this often you could subclass NSScanner or use a category to make the code more elegant.

I think the category-based code would look something like:

NSScanner+MyAdditions.h:

#import "NSScanner.h"

@interface NSScanner (MyAdditions)
  - (BOOL)my_scanCGFloat:(CGFloat *) cgFloatValue
@end

NSScanner+MyAdditions.m:

#import "NSScanner+MyAdditions.h"

@implementation NSScanner (MyAdditions)
  - (BOOL)my_scanCGFloat:(CGFloat *) cgFloatValue {
#if CGFLOAT_IS_DOUBLE 
    return [self scanDouble:cgFloatValue]; 
#else 
    return [self scanFloat:cgFloatValue]; 
#endif
}
@end