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From: Jorge Almeida <jjalmeida@gmail.com>
Newsgroups: gmane.linux.lib.musl.general
Subject: RTC_RD_TIME
Date: Tue, 29 Aug 2017 22:28:14 +0100
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Archived-At: <http://permalink.gmane.org/gmane.linux.lib.musl.general/11864>

A function to read the hardware clock (the battery powered thingy in
the motherboard):

(man 4 rtc)

void read_hw(struct rtc_time* rtctime){
   int rtcfd=open("/dev/rtc0" , O_RDONLY);
   ioctl(rtcfd, RTC_RD_TIME, rtctime);
   close(rtcfd);
}

(error checking omitted)

The problem:
warning: overflow in implicit constant conversion [-Woverflow]

(an arrow pointing to RTC_RD_TIME)

The same program compiles without warnings with glibc and dietlibc.

Headers:

#define _DEFAULT_SOURCE
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <time.h>
#include <linux/unistd.h>
#include <math.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <linux/vt.h>
#include <linux/rtc.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>

TIA

Jorge Almeida