OC中NSString 的常用方法

 NSString *str1 = @"BeiJing";
    NSString *str2 = @"beijing";
    
    //全部轉爲大寫
    NSLog(@"%@",[str1 uppercaseString]);
    
    //全部轉爲小寫
    NSLog(@"%@",[str1 lowercaseString]);
    
    //首字母大寫
    NSLog(@"%@",[str1 capitalizedString]);
    
    //比較兩個字符串內容是否相同
    BOOL b =[str1 isEqualToString:str2];
    
    //兩個字符串內容比較
    //NSOrderedAscending    右邊 > 左邊
    //NSOrderedSame         內容相同
    //NSOrderedDescending   左邊 > 右邊
    NSComparisonResult result = [str1 compare:str2];
    if (result == NSOrderedAscending) {
        NSLog(@"右邊 > 左邊");
    }else if(result == NSOrderedSame){
        NSLog(@"內容相同");
    }else if (result == NSOrderedDescending){
        NSLog(@"左邊 > 右邊");
    }
    
    //忽略大小寫進行比較，返回值與compare一樣
    result = [str1 caseInsensitiveCompare:str2];
    if (result == NSOrderedAscending) {
        NSLog(@"右邊 > 左邊");
    }else if(result == NSOrderedSame){
        NSLog(@"內容相同");
    }else if (result == NSOrderedDescending){
        NSLog(@"左邊 > 右邊");
    }
    
    //判斷字符串是否以指定字符串開頭
    [str1 hasPrefix:@"aaa"];
    //判斷字符串是否以指定字符串結尾
    [str1 hasSuffix:@"aaa"];
    
    //判斷字符串是否包含指定字符串，返回位置和長度
    NSRange range = [@"123456" rangeOfString:@"456"];
    NSLog(@"%@", NSStringFromRange(range));
    
    //反向搜索
    range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch];
    NSLog(@"%@",NSStringFromRange(range));
    
    //指定範圍進行搜索
    range = NSMakeRange(0, 9);
    range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch range:range];
    NSLog(@"%@",NSStringFromRange(range));

//字符串的截取
        NSString *str = @"123456789";
        NSLog(@"%@",[str substringFromIndex:3]);
        NSLog(@"%@",[str substringToIndex:6]);
        NSLog(@"%@",[str substringWithRange:NSMakeRange(3, 3)]);
        
        //用指定字符串分割字符串，返回一個數組
        NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];
        NSLog(@"%@",array);
        
        //將數組中的字符串組合成一個文件路徑
        NSMutableArray *components = [NSMutableArray array];
        [components addObject:@"Users"];
        [components addObject:@"CentralPerk"];
        [components addObject:@"Desktop"];
        NSString *path = [NSString pathWithComponents:components];
        NSLog(@"%@",path);  //Users/CentralPerk/Desktop
        
        //將一個路徑分割成一個數組
        NSArray *array1 = [path pathComponents];
        NSLog(@"%@",array1);
        
        //判斷是否爲絕對路徑(依據：是否以'/'開始)
        path = @"/Users/CentralPerk/Desktop";
        NSLog(@"%i",[path isAbsolutePath]);
        
        //獲取最後一個目錄
        NSLog(@"%@",[path lastPathComponent]);
        
        //刪除最後一個目錄
        NSLog(@"%@",[path stringByDeletingLastPathComponent]);
        
        //拼接一個目錄
        NSLog(@"%@",[path stringByAppendingPathComponent:@"aaa"]);   ///Users/CentralPerk/Desktop/aaa
        NSLog(@"%@",[path stringByAppendingString:@"aaa"]);      ///Users/CentralPerk/Desktopaaa
        NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);  ///Users/CentralPerk/Desktopbc
        
        //拓展名出來
        //獲取拓展名,不帶.
        NSString *str2 = @"Users/CentralPerk/Desktop/test.txt";
        NSLog(@"%@",[str2 pathExtension]);
        //添加拓展名,不需要帶.
        NSLog(@"%@",[str2 stringByAppendingPathExtension:@"mp3"]);
        //刪除拓展名,帶.一塊刪除
        NSLog(@"%@",[str2 stringByDeletingPathExtension]);
        
        //字符串轉爲 int double float
        NSString *str3 = @"123";
        NSLog(@"%i",[str3 intValue]);
        NSLog(@"%zi",[str3 length]);
        
        //取出指定位置的字符
        unichar c = [str3 characterAtIndex:2];
        NSLog(@"%c",c);
        
        //轉爲C語言的字符串
        const char *s = [str3 UTF8String];
        NSLog(@"%s",s);