When a String is not a String?

[mistergreen2011]

Ok, I'm really confused with this one.

I have a NSMutable array it looks like this.

{
    Fe = "0.1";
    name = "DTPA Fe (10%)";
    target = Fe;
    tsp = 4290;
}........

I want to grab the objectKey name and do some comparisons.

//shared.elements is above
NSArray *temp = [[shared.elements objectAtIndex:i] allKeys];
// temp gives me Fe,name,target,tsp

for(int j=0; j < [temp count]; j++) {
        //making sure it's a string!!!
        if ([[temp objectAtIndex:j] isKindOfClass:[NSString class]]) {
            NSLog(@"yes i'm a string");
        }

        if([(NSString *)[temp objectAtIndex:j] lowercaseString] == @"name") {
            NSLog(@"expletive");
            // nothing
        }

   if([temp objectAtIndex:j] == @"name") {
            NSLog(@"expletive");
            // nothing
        }
       
    }

None of the conditions are true except that it's a confirmation it's a NSString.

confused.

[Duncan C]

Originally Posted by mistergreen2011

Ok, I'm really confused with this one.

I have a NSMutable array it looks like this.

{
    Fe = "0.1";
    name = "DTPA Fe (10%)";
    target = Fe;
    tsp = 4290;
}........

I want to grab the objectKey name and do some comparisons.

//shared.elements is above
NSArray *temp = [[shared.elements objectAtIndex:i] allKeys];
// temp gives me Fe,name,target,tsp

for(int j=0; j < [temp count]; j++) {
        //making sure it's a string!!!
        if ([[temp objectAtIndex:j] isKindOfClass:[NSString class]]) {
            NSLog(@"yes i'm a string");
        }

        if([(NSString *)[temp objectAtIndex:j] lowercaseString] == @"name") {
            NSLog(@"expletive");
            // nothing
        }

   if([temp objectAtIndex:j] == @"name") {
            NSLog(@"expletive");
            // nothing
        }
       
    }

None of the conditions are true except that it's a confirmation it's a NSString.

confused.

You can't use == to compare objects. (NSStrings are objects).

In Objective C, a variable that refers to an instance of an object is actually a pointer.

So when you say

MyObject *anObject = [MyObject alloc] init];

the "anObject" variable is actually a pointer to the memory address of an object of type MyObject.

When you use == to compare 2 objects, you are actually comparing 2 pointer variables. The only time

if (objectA == objectB)

will evaluate as TRUE is if the variables objectA and objectB point to the same address.

To compare strings, use code like this:

if ([string1 isEqualToString: @"string"])
{
  //strings are equal, do something
}

Note that you have the same problem in trying to compare 2 C strings.

If you have code like this

char *aString = "foo";

char *bString = "foo";

if (aString == bString) 
{
  //won't work
}

Will not work, because the if statement compares the addresses of aString and bString,
not the string contents.


To compare 2 C strings, you use the strcmp function:

char *aString = "foo";

char *bString = "foo";

if (strcmp(aString,bString))
{
  //C strings are equal
}

[Domele]

To compare strings, you need to use isEqualToString:. "==" compares memory addresses. isEqualToString will compare the actual values of the strings.

[mistergreen2011]

ah! thanks folks.