Question

是否有可能printf C中数组第一个元素的内存地址？

当我尝试：

时，编译器报告错误

printf("i%/n", @array[0])

我已宣布array[] = {23, 56, 78}。

Answer 1

你有没有尝试过：

printf("%p\n", (void*)array);

Answer 2

fn main() {
    let filename = "tt.txt";

    // open a tt.txt file in the local directory
    let file = OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .open(filename)
        .unwrap();

    // now read the whole file to get the latest state
    let date_re = Regex::new(r"^(\d{4})-(\d{2})-(\d{2})").unwrap();
    let time_activity_re = Regex::new(r"^(\d{2}):(\d{2})\s*(.*)").unwrap();
    let reader = BufReader::new(file);
    let mut latest_date: Option<Date<Local>> = None;
    let mut latest_datetime: Option<DateTime<Local>> = None;
    let mut latest_activity: Option<String> = None;

    for wrapped_line in reader.lines() {
        let line = wrapped_line.unwrap();
        println!("line: {}", line);

        if date_re.is_match(&line) {
            let captures = date_re.captures(&line).unwrap();
            let year = captures.at(1).unwrap().parse::<i32>().unwrap();
            let month = captures.at(2).unwrap().parse::<u32>().unwrap();
            let day = captures.at(3).unwrap().parse::<u32>().unwrap();
            latest_date = Some(Local.ymd(year, month, day));
            latest_datetime = None;
            latest_activity = None;
        }

        if time_activity_re.is_match(&line) && latest_date != None {
            let captures = time_activity_re.captures(&line).unwrap();
            let hour = captures.at(1).unwrap().parse::<u32>().unwrap();
            let minute = captures.at(2).unwrap().parse::<u32>().unwrap();
            let activity = captures.at(3).unwrap();

            latest_datetime = Some(latest_date.unwrap().and_hms(hour, minute, 0));

            latest_activity = if activity.len() > 0 {
                // TODO: if latest_activity already constains a string, clear it and reuse it
                // as per: https://stackoverflow.com/questions/33781625/how-to-allocate-a-string-before-you-know-how-big-it-needs-to-be
                Some(activity.to_string())
            } else {
                None
            };

            println!("time activity: {} |{}|", latest_datetime.unwrap(), activity);
        }
    }

    // FIXME: I have to open a second file descriptor to the same file, in order to be able to write to it
    let mut out = OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .open(filename)
        .unwrap();

    out.seek(End(0));

    let now = Local::now();
    if latest_date == None || latest_date.unwrap().year() != now.year()
        || latest_date.unwrap().month() != now.month()
        || latest_date.unwrap().day() != now.day()
    {
        if (latest_date != None) {
            // not an empy file, as far as tt is concerned
            out.write_all(b"\n\n");
        }
        out.write_all(format!("{}\n", now.format("%Y-%m-%d")).as_bytes());
        out.write_all(b"\n");
    }

    let activity = env::args().skip(1).join(" ");
    if (activity.len() > 0) {
        out.write_all(format!("{} {}\n", now.format("%H:%M"), activity).as_bytes());
    } else {
        // if there was no latest activity *and* there is no activity, then there's no point in writing a second blank line with just a time
        if latest_activity == None {
            return;
        }
        out.write_all(format!("{}\n", now.format("%H:%M")).as_bytes());
    }

    // FIXME: we're just relying on the program exit to close the two file descriptors (which point at the same file).
}

应该是

printf("i%/n", @array[0])

使用格式说明符printf("%p\n", (void*)&array[0]);打印地址

Answer 3

使用%p格式说明符。使用&代替@来获取地址，虽然这是多余的：&foo[0]等于foo，除非是sizeof的操作数。从技术上讲，你还需要将数组指针转换为void*，除非它是指向字符（char*）的指针，在这种情况下不需要强制转换：

printf("%p\n", (void*)array);

是否可以在C中打印数组第一个元素的内存地址？

3 个答案: