macOS Obj-c finding index of character in NSString

lee1210 said:

Not that anyone asked, but this also seemed like a case that you could extend NSString to provide extra functionality.

I then found out that actually extending NSString is a really bad idea (but not until I had done so and had this working), so I made a class using composition instead.

Using NS for your own classes isn't a good idea, I was just playing with this.

The result:

NSExtendedString.m:

Code:

#import "NSExtendedString.h"

@implementation NSExtendedString

-(unsigned int) indexOf:(char) searchChar {
  NSRange searchRange;
  searchRange.location=(unsigned int)searchChar;
  searchRange.length=1;
  NSRange foundRange = [backingString rangeOfCharacterFromSet:[NSCharacterSet characterSetWithRange:searchRange]];
  return foundRange.location;
}

-(NSExtendedString *) initWithString: (NSString *) origString {
  if(self = [super init]) {
    backingString = [[NSString alloc] initWithString:origString];
  }
  return self;
}
-(NSExtendedString *) initWithExtendedString: (NSExtendedString *) origString {
  if(self = [super init]) {
    backingString = [[origString string] copy];
  }
  return self;
}

-(NSString *) string {
  return backingString;
}
@end

NSExtendedString.h:

Code:

#import <Foundation/Foundation.h>

@interface NSExtendedString : NSObject {
  NSString *backingString;
}
- (unsigned int) indexOf:(char) searchChar;
-(NSExtendedString *) initWithString: (NSString *) origString;
-(NSExtendedString *) initWithExtendedString: (NSExtendedString *) origString;
-(NSString *) string;


@end

TestNewString.m:

Code:

#import <Foundation/Foundation.h>
#import "NSExtendedString.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    NSExtendedString *myString = [[NSExtendedString alloc] initWithString:@"Test:string+number-one"];
	unsigned int colonPosition = [myString indexOf:':'];
	unsigned int plusPosition = [myString indexOf:'+'];
	unsigned int minusPosition = [myString indexOf:'-'];
	NSLog(@"The position of the first colon is: %u, the position of the first plus is: %u, the position of the first minus is: %u",colonPosition,plusPosition,minusPosition);
	NSExtendedString *stringTwo = [[NSExtendedString alloc] initWithExtendedString:myString];
	unsigned int plusPositionTwo = [stringTwo indexOf:'+'];
	NSLog(@"Testing copy: %u",plusPositionTwo);
    [pool release];
    return 0;
}

I'm on 10.4, so the proper type for most everything in 10.5 and above would be NSUInteger rather than unsigned int.

-Lee

Click to expand...

@interface NSString (indexOfChar)
- (unsigned int) indexOfChar: (char) toFind;
@end

@implementation NSString (indexOfChar)
// will return NSNotFound if not in the string
- (unsigned int) indexOfChar: (char) toFind {
     // you could experiment with this, I suspect linear searching each 
     // character would be about as fast as it can get.
     NSString *substring = [NSString stringWithFormat: @"%c", toFind];
     NSRange range = [self rangeOfString: substring];
     return range.location;
}
@end

// call like...
NSString *s = @"some string";
unsigned int index = [s indexOfChar: 'm'];
if (index != NSNotFound) {
...

jared_kipe said:

To be fair, not that anyone asked, I don't really see the reason to extend NSString at all in this case to provide this functionality. Well not by subclassing anyway since Objective-C has such a nice way of giving existing classes new methods.

Code:

@interface NSString (indexOfChar)
- (unsigned int) indexOfChar: (char) toFind;
@end

@implementation NSString (indexOfChar)
// will return NSNotFound if not in the string
- (unsigned int) indexOfChar: (char) toFind {
     // you could experiment with this, I suspect linear searching each 
     // character would be about as fast as it can get.
     NSString *substring = [NSString stringWithFormat: @"%c", toFind];
     NSRange range = [self rangeOfString: substring];
     return range.location;
}
@end

// call like...
NSString *s = @"some string";
unsigned int index = [s indexOfChar: 'm'];
if (index != NSNotFound) {
...

Click to expand...

lee1210 said:

To be fair (to me) I wrote that in 2008. I was embarrassed to see that not-category business when I looked at this thread, but feel better that it was so old (if you're not getting better...).

-Lee

Click to expand...