OC—字符串

說明：

OC中字符串是對C語言字符串的封裝，字符串分爲不可變字符串和可變字符串，分別對應NSString和NSMutableString兩個類，NSMutableString繼承自NSString，所以NSMutableString擁有NSString的大部分方法。

在OC中，字符串，數組，字典等常用數據類型對象都有不可變類型和可變類型。

一：NSString的創建方式

NSString的創建可分爲兩種，一種是類方法，一種是類型方法。

//方式一
    NSString *str = @"ahello world!";
    NSString *strcmp = @"hello world!";
    NSLog(@"%@", str);
    //方式二
    NSString *str2 = [[NSString alloc] initWithString:strcmp];
    NSString *str22 = [NSString stringWithString:str];
    NSLog(@"%@", str22);
    NSLog(@"%@", str2);
    //方式三
    NSString *str3 = [[NSString alloc] initWithUTF8String:s];
    NSString *str33 = [NSString stringWithUTF8String:s];
    NSLog(@"%@", str3);
    NSLog(@"%@", str33);
    //方式四
    NSString *str4 = [[NSString alloc] initWithFormat:@"%d%@%f",5,str3,4.9];
    NSString *str44 = [NSString stringWithFormat:@"%d%@%f",5, str3,4.9];
    NSLog(@"%@", str4);
    NSLog(@"%@", str44);

二.NSStrig的常用方法

//比較兩個字符串是否相等
    BOOL equal = [str isEqualToString:str2];
    if (equal) {
        NSLog(@"str == str2");
    }else{
        NSLog(@"str != str2");
    }
    //獲取字符串的長度
    NSUInteger len = [str length];
    NSLog(@"len=%ld", len);
    //比較兩個字符串的大小
    NSComparisonResult result = [str compare:str2];
    if(result==NSOrderedSame){
        NSLog(@"字符串相等");
    }else if(result == NSOrderedAscending){
        NSLog(@"str小於str2");
    }else if(result == NSOrderedDescending){
        NSLog(@"str大於str2");
    }
    //提取字串
    NSString *string = @"I love ios system!";
    
    NSString *string1 = [string substringFromIndex:2 ];
    NSLog(@"%@",string);//string 的值不變，因爲NSString不可變
    NSLog(@"%@", string1);//包括下表2
    
    NSString *string3 = [string substringToIndex:9];
    NSLog(@"%@",string3);//不包括下標9
    
    //從下標0開始，截取5個字符
    NSString *string4 = [string substringWithRange:NSMakeRange(0, 5)];
    NSLog(@"%@",string4);
    
    unichar c = [string characterAtIndex:0];
    NSLog(@"%C", c);//下標0對應點字符
    
    NSRange range =[string rangeOfString:@"love"];
    NSLog(@"range.location = %ld, range.length=%ld", range.location, range.length);
    NSRange range1 = [string rangeOfString:@"haha"];
    if(range1.location == NSNotFound){
        NSLog(@"不存在");
    }
    
    //追加字符串
    NSString *string11 = [string stringByAppendingString:@"dsfsdf"];
    NSLog(@"%@", string11);
    NSString *string12 = [string stringByAppendingFormat:@"%d%f", 5, 5.0];
    NSLog(@"%@", string12);
    
    NSString *string13 = [str stringByAppendingPathComponent:@"123"]; // /路徑
    NSString *string14 = [str stringByAppendingPathExtension:@"234"]; // .路徑
    NSLog(@"%@", string13);
    NSLog(@"%@", string14);
三.NSMutableString的創建
NSMutableString的創建方式和NSString的創建方式類似。
//創建一個空的可變字符串
    NSMutableString *str = [[NSMutableString alloc] init];
    NSLog(@“str=%p",str);
四.NSMutableString的常用方法
[str setString:@"hello World!"];
    NSLog(@"str=%@ str = %p",str, str);
    
    //插入
    [str insertString:@"HAHA" atIndex:6];
    NSLog(@"str=%@ str = %p",str, str);
    
    //刪除
    [str deleteCharactersInRange:NSMakeRange(1, 5)];
    NSLog(@"%@", str);
    
    //追加
    [str appendString:@"i am a bad men"];
    NSLog(@"%@", str);
    [str appendFormat:@"%d%@..",1,@"so bad men!" ];
    NSLog(@"%@", str);
    [str replaceCharactersInRange:NSMakeRange(2, 4) withString:@"~~~~~~~~"];
    NSLog(@"%@",str);
    
    NSMutableString *s = [[NSMutableString alloc] init];
    [s setString:@"卡哈卡哈卡哈卡哈卡啊"];
    NSLog(@"%@", s);
    [s replaceOccurrencesOfString:@"卡哈" withString:@"hello" options:NSLiteralSearch range:[s rangeOfString:s]];
    
    NSLog(@"%@", s);