How can I check specific macro is there or not with identifier stored inside NSString

Question

I have macros named

CONSTANT_1
CONSTANT_2
CONSTANT_3
CONSTANT_4 etc..

I have an NSString variable sending from another class consist of macro name only, how can I access the contents of macro variable matching with this NSString.

My NSString variable is defined as:

NSString *str=@"CONSTANT_3"

Answer 1

1 Here is one solution to do it, but it needs you to know all macros:

#define CONSTANT_1 1
#define CONSTANT_2 2
#define CONSTANT_3 3

#define STRINGIZE(x) #x

+ (int)getValueForContant:(NSString *)constantStr {
    const char *charStr = STRINGIZE(CONSTANT_1);
    NSString *str = [NSString stringWithUTF8String:charStr];
    if ([constantStr isEqualToString:str]) {
        return CONSTANT_1;
    }

    charStr = STRINGIZE(CONSTANT_2);
    str = [NSString stringWithUTF8String:charStr];
    if ([constantStr isEqualToString:str]) {
        return CONSTANT_2;
    }

    return -1;
}

And use it as:

int constVal = [ClassName getValueForContant:@"CONSTANT_1"];

It'll give you int value in return.

2 Use .plist to define constants and loop through to get appropriate value as provided string parameter to this method;

+ (int)getValueForContant:(NSString *)constantStr

Answer 2

I would recommend to better use constants

NSString *const CONSTANT_1 = @"1";
NSString *const CONSTANT_2 = @"2";
NSString *const CONSTANT_3 = @"3";

The you could use CFBundleGetDataPointerForName

-(NSString *)valueOfConstantWithName:(NSString *)constantName {
    void ** pointer = CFBundleGetDataPointerForName(CFBundleGetMainBundle(),   (__bridge CFStringRef)constantName);
    return (__bridge NSString *)(pointer ? *pointer : nil);
}

and use that method like

NSString *costant1 = [self valueOfConstantWithName:@"CONSTANT_1"];