I have Constants NSString, that I want to call like:
[newString isEqualToString:CONSTANT_STRING]; Any wrong code here?
I got this warning:
sending 'const NSString *' to parameter of type 'NSString *' discards qualifiers
How should these be declared?
You should declare your constant string as follows:
NSString * const kSomeConstantString = @""; // constant pointer instead of:
const NSString * kSomeConstantString = @""; // pointer to constant // equivalent to NSString const * kSomeConstantString = @""; The former is a constant pointer to an NSString object, while the latter is a pointer to a constant NSString object.
Using a NSString * const prevents you from reassigning kSomeConstantString to point to a different NSString object.
The method isEqualToString: expects an argument of type NSString *. If you pass a pointer to a constant string (const NSString *), you are passing something different than it expects.
Besides, NSString objects are already immutable, so making them const NSString is meaningless.
const qualifier applies to the term on its left, and it applies to the term on its right only if there's nothing on its left side (e. g. const char * and a char const * are non-const pointers to const char, but char *const is a const pointer to non-const char).
just to put all on one place which found on various post on stackoverflow and works for me , #define is bad because you cannot benefit from variable types, basically the compiler replaces all occurrence when compiles (import Constants.h whenever you need) :
// Constants.h #import <Foundation/Foundation.h> @interface Constants : NSObject extern NSString *APP_STATE_LOGGED_IN; extern NSString *APP_STATE_LOGGED_OUT; @end // Constants.m #import <Foundation/Foundation.h> #import "Constants.h" @implementation Constants NSString *APP_STATE_LOGGED_IN = @"APP_STATE_LOGGED_IN"; NSString *APP_STATE_LOGGED_OUT = @"APP_STATE_LOGGED_OUT"; @end spare few minutes to read this. A goodread on pointers hell on constants and vice-versa.
