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 0;
}

//
//  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:3];
        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:5];
        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:8] substringToIndex:6];
        NSLog(@"Chars from index 8 through 13: %@",res);
        
        //更简单的方法
        res = [str1 substringWithRange:NSMakeRange(8, 6)];
        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 0;
}

　　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:7];
        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(16, 13)];
        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(8, 8) 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 0;
}