NSString

// —————————NSString

        // NSString

        //1.初始化:直接字符串、格式化字符串、文件读取内容初始化

        NSString *str1 = @"hello world!";

        NSString *str2 = [NSString stringWithFormat:@"start to printf: %@", str1];

        NSString *str3 = [[NSString alloc] initWithContentsOfFile:@"/user/document/test.txt" encoding:NSUTF8StringEncoding error:nil];

        

        // 字符串写入文件

        [str1 writeToFile:@"/user/document/test.txt" atomically:YES];

        

        // 字符串大写、小写、首字母大写

        str1 = [str1 uppercaseString];

        str1 = [str1 lowercaseString];

        str1 = [str1 capitalizedString];

        

        //字符串截取

        str2 = [str1 substringFromIndex:5];

        NSLog(@"string = %@", str2);

        str2 = [str1 substringToIndex:5];

        NSLog(@"string = %@", str2);

        str2 = [str1 substringWithRange:NSMakeRange(0, 7)];

        NSLog(@"string = %@", str2);

        // 字符串是否以另一字符串开头或结尾

        BOOL isStart = [str1 hasPrefix:@"hello"];

        NSLog(@"isStart is : %i", isStart);

        BOOL isEnd = [str1 hasSuffix:@"world!"];

        NSLog(@"isEnd is : %i", isEnd);

        

        // 获取文件后缀名

        NSString *filePath = @"/document/test.txt";

        NSString *ext = [filePath pathExtension];

        NSLog(@"ext is : %@", ext);

        

        // 字符串转整形

        NSString *value = @"100";

        int va = [value intValue];

        NSLog(@"va is : %i", va);

        // 字符串替换

        str1 = [str1 stringByReplacingOccurrencesOfString:@"hello" withString:@"bye bye"];

        // 字符串转整

        int intVal = [str1 intValue];

        NSLog(@"str to int : intVal= %i", intVal);

        str1 = [[NSNumber numberWithInteger:intVal] stringValue];

        NSLog(@"int to str = %@", str1);

        

        // 字符串分割

        NSString *splitStr = @"test1;test2;test3;test4";

        NSArray *array = [splitStr componentsSeparatedByString:@";"];

        NSLog(@"%@", array);

        

        // 可变字符串

        NSMutableString *mulStr = [[NSMutableString alloc] initWithCapacity:1];

        [mulStr appendString:@"test1"];

        [mulStr appendFormat:@"test2"];

        [mulStr insertString:@";" atIndex:5];

        [mulStr replaceCharactersInRange:NSMakeRange(0, 4) withString:@"replace test"];

        [mulStr deleteCharactersInRange:NSMakeRange(0, 4)];

        

        // 查找字符串包含

        NSRange range = [mulStr rangeOfString:@"test"];

        NSLog(@"location : %ld", range.location);

        

        NSLog(@"mulStr is : %@", mulStr);

       // 字符串比较  小于：-1 等于：0 大于：1

    NSString *comStr1 = @"bbc";

    NSString *comStr2 = @"bbc";

    NSComparisonResult result = [comStr1 compare:comStr2];

    NSLog(@"result=%ld", result);