我如何在C中获得昨天的日期？

#include <stdio.h>
#include <time.h>

int main()
{
    struct tm tm = {0};
    tm.tm_year = 2022 - 1900;
    tm.tm_mon = 9;
    tm.tm_mday = 10;
    tm.tm_hour = 12;
    tm.tm_min = 0;
    tm.tm_sec = 0;

    time_t now = mktime(&tm);
    now -= 86400;  // 减去1秒

    printf("Today: %s", ctime(&now));
    printf("Yesterday: %s", ctime(&now-86400));

    return 0;
}

Today: Mon Oct 10 12:00:00 2022
Yesterday: Sun Oct 09 12:00:00 2022