Linux C语言实现获取设备运行时间并转换成xxdxxhxxmxxs的格式

可以使用下面的代码实现将系统运行时间转换成 `xxdxxhxxmxxs` 格式：

#include <stdio.h>
#include <stdlib.h>

#define SECONDS_PER_DAY 86400
#define SECONDS_PER_HOUR 3600
#define SECONDS_PER_MINUTE 60

int main() {
    double uptime;
    int days, hours, minutes, seconds;
    FILE *fp = fopen("/proc/uptime", "r");
    if (fp == NULL) {
        perror("Unable to read uptime\n");
        exit(EXIT_FAILURE);
    }
    fscanf(fp, "%lf", &uptime);
    fclose(fp);

    days = (int)(uptime / SECONDS_PER_DAY);
    hours = (int)((uptime - days * SECONDS_PER_DAY) / SECONDS_PER_HOUR);
    minutes = (int)((uptime - days * SECONDS_PER_DAY - hours * SECONDS_PER_HOUR) / SECONDS_PER_MINUTE);
    seconds = (int)(uptime - days * SECONDS_PER_DAY - hours * SECONDS_PER_HOUR - minutes * SECONDS_PER_MINUTE);

    printf("System uptime: %dd%02dh%02dm%02ds\n", days, hours, minutes, seconds);

    return 0;
}

这个程序首先计算出运行时间对应的天数、小时数、分钟数和秒数，然后使用格式字符串 `%dd%02dh%02dm%02ds` 打印出结果，其中 `%02d` 表示输出两位数字，不足两位时前面补零。