Does const go before or after CGFloat?

Question

Does it even matter? Const before or const after? I'm guessing that whether I put const before or after CGFloat it makes the value of CGFloat constant, but what about the pointer? Is this right for Objective-C:

// Example.h

extern CGFloat const kPasscodeInputBoxWidth;


// Example.m

CGFloat const kPasscodeInputBoxWidth = 61.0f;

Solution 1

It can go either before or after. In the case of a pointer, what matters is whether the const ends up before or after the asterisk:

const int *a;    // pointer to const int -- can't change what a points at
int const *a;    // same

int *const a;    // const pointer to int -- can't change the pointer itself.
                 // Note: must be initialized, since it can't be assigned.

Solution 2

It doesn't matter (I've always used the former, but I guess it's a matter of style):

const CGFloat kPasscodeInputBoxWidth = 61.0;
CGFloat const kPasscodeInputBoxWidth = 61.0;

At least in the current rendition of CGFloat, it's just a typedef of double, so do as you would with a regular primitive datatype. For pointers, the placement of const will determine if it's the pointer or the value that is constant, so for that it does matter.

Comments

[pmg]

You can also have const int *const a;: a read-only pointer to read-only objects :)

[ma11hew28]

CGFloat is actually a float, not a double.

[Gustav Larsson]

I think it varies between 32- and 64-bit systems. I run 64-bit and for me it's a double.

[ma11hew28]

Interesting. I didn't know that. I was just going by line 89 of CGBase.h: typedef CGFLOAT_TYPE CGFloat;, which I got to by command-clicking on CGFloat in Xcode. But, how could the source code be different for you? Shouldn't it be the same on all machines? Hmmm... I thought I was running 64-bit too. How do wou know it's not a double?

[Gustav Larsson]

I'm not sure, I thought I had read that somewhere when you said it was float, but it might be double for everyone. It's not like double requires a 64-bit system. They could theoretically be different even though we have the same source code, through preprocessor defines.

[Max MacLeod]

question relates to CGFloat not integer pointers. For integers, Apple guidelines state "You can use const to create an integer constant if the constant is unrelated to other constants; otherwise, use enumeration.". They only advocate const while using float. See developer.apple.com/library/mac/documentation/Cocoa/Conceptu‌​al/…

[Jerry Coffin]

@MaxMacLeod: The exact type (int, long, float, double, CGFloat, etc.) is pretty much irrelevant here.