Objective-C Strings

The string in Objective-C programming language is represented using NSString and its subclass NSMutableString provides several ways for creating string objects. The simplest way to create a string object is to use the Objective-C @"..." construct:

NSString *greeting = @"Hello";

A simple example for creating and printing a string is shown below.

#import <Foundation/Foundation.h>

int main ()
{
   NSString *greeting = @"Hello";

   NSLog(@"Greeting message: %@\n", greeting );

   return 0;
}

When the above code is compiled and executed, it produces result something as follows:

2013-09-11 01:21:39.922 demo[23926] Greeting message: Hello

Objective-C supports a wide range of methods for manipulate strings:

S.N.	Method & Purpose
1	- (NSString *)capitalizedString; Returns a capitalized representation of the receiver.
2	- (unichar)characterAtIndex:(NSUInteger)index; Returns the character at a given array position.
3	- (double)doubleValue; Returns the floating-point value of the receiver’s text as a double.
4	- (float)floatValue; Returns the floating-point value of the receiver’s text as a float.
5	- (BOOL)hasPrefix:(NSString *)aString; Returns a Boolean value that indicates whether a given string matches the beginning characters of the receiver.
6	- (BOOL)hasSuffix:(NSString *)aString; Returns a Boolean value that indicates whether a given string matches the ending characters of the receiver.
7	- (id)initWithFormat:(NSString *)format ...; Returns an NSString object initialized by using a given format string as a template into which the remaining argument values are substituted.
8	- (NSInteger)integerValue; Returns the NSInteger value of the receiver’s text.
9	- (BOOL)isEqualToString:(NSString *)aString; Returns a Boolean value that indicates whether a given string is equal to the receiver using a literal Unicode-based comparison.
10	- (NSUInteger)length; Returns the number of Unicode characters in the receiver.
11	- (NSString *)lowercaseString; Returns lowercased representation of the receiver.
12	- (NSRange)rangeOfString:(NSString *)aString; Finds and returns the range of the first occurrence of a given string within the receiver.
13	- (NSString *)stringByAppendingFormat:(NSString *)format ...; Returns a string made by appending to the receiver a string constructed from a given format string and the following arguments.
14	- (NSString *)stringByTrimmingCharactersInSet:(NSCharacterSet *)set; Returns a new string made by removing from both ends of the receiver characters contained in a given character set.
15	- (NSString *)substringFromIndex:(NSUInteger)anIndex; Returns a new string containing the characters of the receiver from the one at a given index to the end.

Following example makes use of few of the above-mentioned functions:

#import <Foundation/Foundation.h>

int main ()
{
   NSString *str1 = @"Hello";
   NSString *str2 = @"World";
   NSString *str3;
   int  len ;

   NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

   /* uppercase string */
   str3 = [str2 uppercaseString];
   NSLog(@"Uppercase String :  %@\n", str3 );

   /* concatenates str1 and str2 */
   str3 = [str1 stringByAppendingFormat:@"World"];
   NSLog(@"Concatenated string:   %@\n", str3 );

   /* total length of str3 after concatenation */
   len = [str3 length];
   NSLog(@"Length of Str3 :  %d\n", len );
    
   /* InitWithFormat */
    str3 = [[NSString alloc] initWithFormat:@"%@ %@",str1,str2]; 
    NSLog(@"Using initWithFormat:   %@\n", str3 );
    [pool drain];

   return 0;
}

When the above code is compiled and executed, it produces result something as follows:

2013-09-11 01:15:45.069 demo[30378] Uppercase String :  WORLD
2013-09-11 01:15:45.070 demo[30378] Concatenated string:   HelloWorld
2013-09-11 01:15:45.070 demo[30378] Length of Str3 :  10
2013-09-11 01:15:45.070 demo[30378] Using initWithFormat:   Hello World

You can find a complete list of Objective-C NSString related methods in NSString Class Reference.