Objective-C NSString/字符串

Objective-C编程语言中，提供了使用NSString 和它的子类NSMutableString创建字符串对象的几种方法。创建一个字符串对象最简单的方法是使用 Objective-C 的@"..."构造：

NSString *greeting = @"Hello";

如下是一个简单的例子，用于创建和打印字符串如下所示。

#import <Foundation/Foundation.h>

int main ()
{
   NSString *greeting = @"Hello";
   NSLog(@"Greeting message: %@", greetin);
   return 0;
}

上面的代码编译和执行时，它产生的结果如下：

2016-07-11 11:21:39.922 demo[23926] Greeting message: Hello

Objective-C的支持范围广泛的操作字符串的方法：

S.N.	方法 & 目的
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-yiibai value of the receiver’s text as a double.
4	- (float)floatValue; Returns the floating-yiibai 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.

示例如下：

#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 :  %@", str3 );

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

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

   return 0;
}

上面的代码编译和执行时，它产生的结果如下：

2016-07-11 01:15:45.069 demo[30378] Uppercase String :  WORLD
2016-07-11 01:15:45.070 demo[30378] Concatenated string:   HelloWorld
2016-07-11 01:15:45.070 demo[30378] Length of Str3 :  10
2016-07-11 01:15:45.070 demo[30378] Using initWithFormat:   Hello World