Declaring a string variable

[carbcycle]

Hi,

I'm just starting to learn Objective-C.........very simple question for you...

How do I declare a string variable?

At the moment I am using:

NSString *colour;

But when I go to printf the contents of this variable, nothing is displayed.

I'm writing a small program to try and understand the syntax in objective-c, so please forgive my immaturity in the code below:-

#import <Cocoa/Cocoa.h>
#import <stdio.h>


@interface Cup : NSObject
{
	BOOL empty1;
	NSString *colour;
}

-(void)drinkCup:(BOOL)done;
-(void)paintCup:(id)paint;
-(void)print;

@end

@implementation Cup

-(void)drinkCup:(BOOL)done

{

	empty1 = done;
	
}

-(void)paintCup:(id)paint
{

	colour = paint;
	
}

-(void)print

{

	printf("The cup has been drunk:%i\n", empty1 );
	printf("The cup colour is:%@", colour );
	
	
}



@end


int main(int argc, char *argv[])
{
	Cup *lukesCup = [[Cup alloc] init];
	
	[lukesCup drinkCup: 1];
	[lukesCup paintCup: @"Red"];
	[lukesCup print];
	
	[lukesCup release];
	
    return NSApplicationMain(argc,  (const char **) argv);
	
}

Do I need to init the string as it is based on the class NSString?

Thanks for your help.

[_pi]

use NSLog to output strings

NSString has a class method called stringWithString that takes care of alloc, init and handling the release of the newly allocated string object.

As a rule of thumb: class methods that return a "ready-to-go" object also take care of memory management, so no need to call release on an object created through a class method.


Hope this helps.

[carbcycle]

Originally Posted by _pi

use NSLog to output strings

NSString has a class method called stringWithString that takes care of alloc, init and handling the release of the newly allocated string object.

As a rule of thumb: class methods that return a "ready-to-go" object also take care of memory management, so no need to call release on an object created through a class method.


Hope this helps.

Thank for the quick reply.

I understand what you are saying about "ready-to-go" object but not sure how I would use NSLog in my code. Can you demonstrate?

Cheers.

[_pi]

Originally Posted by carbcycle

Thank for the quick reply.

I understand what you are saying about "ready-to-go" object but not sure how I would use NSLog in my code. Can you demonstrate?

Cheers.

Sure. It's important to keep in mind, that NSLog simply takes 1 NSString object, so you either need to concatenate multiple strings together using the method "stringByAppendingString" or you can create one yourself using [NSString stringWithFormat] which allows to use placeholders (such as %d, %f, %@, and so on)

NSString *s = [NSString stringWithString:@"this is the content of the string"];	

NSLog([[NSString stringWithString:@"the string contains: "] stringByAppendingString:s]);

NSLog([NSString stringWithFormat:@"the string contains: %@", s]);

Hope this helps.

[carbcycle]

Originally Posted by _pi

Sure. It's important to keep in mind, that NSLog simply takes 1 NSString object, so you either need to concatenate multiple strings together using the method "stringByAppendingString" or you can create one yourself using [NSString stringWithFormat] which allows to use placeholders (such as %d, %f, %@, and so on)

NSString *s = [NSString stringWithString:@"this is the content of the string"];	

NSLog([[NSString stringWithString:@"the string contains: "] stringByAppendingString:s]);

NSLog([NSString stringWithFormat:@"the string contains: %@", s]);

Hope this helps.

Thats great thank you.

[Kalimba]

FYI, you can use printf() to display NSString strings. You just have to make the proper conversion, as follows:

NSString * myString = @"This is my string."

printf( "myString is '%s'\n", [myString UTF8String] );