Objective－C 笔记 字符串操作

　　这次总结下OC里一些对字符串的一些操作。

　　创建字符串对象时，会创建一个内容不可更改的对象，称为不可变对象。可以使用NSString类处理不可变字符串。你经常需要处理字符串并更改字符串中的字符。例如，可能希望从字符串中删除一些字符，或对字符串执行搜索替换操作。这种类型的字符串是使用NSMutableString类处理的。

 //
 //  main.m
 //  Number_String_List_15
 //
 //  Created by SeanAstin on 15/12/30.
 //  Copyright © 2015年 SeanAstin. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 int main(int argc, const char * argv[]) {
     @autoreleasepool {
         NSString *str1 = @"This is string A";
         NSString *str2 = @"This is string B";
         NSString *res;
         NSComparisonResult  compareResult;

         //计算字符串中的值
         NSLog(@"Length of str1: %lu",[str1 length]);

         //将一个字符串复制到另一个字符串
         res = [NSString stringWithString:str1];
         NSLog(@"copy: %@",res);

         //将一个字符串复制到另一个字符串的末尾
         str2 = [str1 stringByAppendingString:str1];
         NSLog(@"Concatentation: %@",str2);

         //验证两个字符串是否相等
         if([str1 isEqualToString:res] == YES)
             NSLog(@"str1 == res");
         else
             NSLog(@"str1 != res");

         //验证一个字符串是否小于、等于或大于另一个字符串
         compareResult = [str1 compare:str2];
         if(compareResult ==  NSOrderedAscending)
             NSLog(@"str1 < str2");
         else if(compareResult == NSOrderedSame)
             NSLog(@"str1 == str2");
         else//必须是NSorderedDescending
             NSLog(@"str1 > str2");

         //将字符串转换为大写
         res = [str1 uppercaseString];
         NSLog(@"Uppercase conversion: %s",[res UTF8String]);

         //将字符串转换为小写
         res = [str1 lowercaseString];
         NSLog(@"Lowercase conversion: %@",res);
     }
     return ;
 }

 //
 //  main.m
 //  Number_String_List_15
 //
 //  Created by SeanAstin on 15/12/30.
 //  Copyright © 2015年 SeanAstin. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 int main(int argc, const char * argv[]) {
     @autoreleasepool {
         NSString *str1 = @"This is string A";
         NSString *str2 = @"This is string B";
         NSString *res;
         NSRange subRange;

         //从字符串中提取前3个字符
         res = [str1 substringToIndex:];
         NSLog(@"First 3 chars of str1: %@",res);

         //提取从索引5开始直到结尾的子字符串
         res = [str1 substringFromIndex:];
         NSLog(@"Chars from index 5 of str1: %@",res);

         //提取从索引8开始索引到13的子字符串（6个字符）
         res = [[str1 substringFromIndex:] substringToIndex:];
         NSLog(@"Chars from index 8 through 13: %@",res);

         //更简单的方法
         res = [str1 substringWithRange:NSMakeRange(, )];
         NSLog(@"Chars from index 8 through 13: %@",res);

         //从另一个字符串中查找一个字符串
         subRange = [str1 rangeOfString:@"string A"];
         NSLog(@"String is at index %lu, length is %lu",subRange.location,subRange.length);
         subRange = [str1 rangeOfString:@"string B"];
         if(subRange.location == NSNotFound)
             NSLog(@"String not found");
         else
             NSLog(@"String is at index %lu, length is %lu",subRange.location,subRange.length);

     }
     return ;
 }

　　NSMutableString类可以用来创建可以更改字符的字符串对象。因为是 NSString类的子类，所以可以使用NSString类的所有方法。

　　在讲述可变于不可变字符串对象时，我们谈到了更改字符串中的实际字符。任意一个可变或不可变字符串对象在程序执行期间，总是可以被设为完全不同的字符串对象的。

 //
 //  main.m
 //  Number_String_List_15
 //
 //  Created by SeanAstin on 15/12/30.
 //  Copyright © 2015年 SeanAstin. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 int main(int argc, const char * argv[]) {
     @autoreleasepool {
         NSString *str1 = @"This is string A";
         NSString *search,*replace;
         NSMutableString *mstr;
         NSRange substr;

         //从不可变字符串创建可变字符串

         mstr = [NSMutableString stringWithString:str1];
         NSLog(@"%@",mstr);

         //插入字符
         [mstr insertString: @" mutable" atIndex:];
         NSLog(@"%@",mstr);

         //插入末尾进行有效拼接
         [mstr insertString:@" and string B" atIndex:[mstr length]];
         NSLog(@"%@",mstr);

         //直接使用appendString
         [mstr appendString:@" and string C"];
         NSLog(@"%@",mstr);

         //根据范围删除子字符串
         [mstr deleteCharactersInRange:NSMakeRange(, )];
         NSLog(@"%@",mstr);

         //查找然后将其删除
         substr =  [mstr rangeOfString:@"string B and "];
         if(substr.location != NSNotFound){
             [mstr deleteCharactersInRange:substr];
             NSLog(@"%@",mstr);
         }

         //直接设置为可变的字符串
         [mstr setString:@"This is string A"];
         NSLog(@"%@",mstr);

         //替换一些字符
         [mstr replaceCharactersInRange:NSMakeRange(, ) withString:@"a mutable string"];
         NSLog(@"%@",mstr);

         //查找和替换
         search = @"This is";
         replace = @"An example";
         substr = [mstr rangeOfString: search];
         if(substr.location != NSNotFound){
             [mstr replaceCharactersInRange:substr withString:replace];
             NSLog(@"%@",mstr);
         }

         //查找和替换所有匹配项
         search = @"a";
         replace = @"X";
         substr = [mstr rangeOfString:search];
         while(substr.location != NSNotFound){
             [mstr replaceCharactersInRange:substr withString:replace];
             substr = [mstr rangeOfString:search];

         }
         NSLog(@"%@",mstr);
     }
     return ;
 }