[LINUX] How to display the modification date of a file in C language up to nanoseconds

It is a method to display the modification date and time of the file in C language up to nanoseconds. The purpose is to check for regular updates of files.

About the environment

-Linux kernel 2.5.48 or higher -File system XFS, JFS, Btrfs, ext4 File systems other than the above may display nanoseconds as 0.



#include <stdio.h>
#include <sys/stat.h>
#include <errno.h>
#include <time.h>

int main(int argc, char *argv[])
    int i;
    struct stat st;
    char date_str[256];

    /* argc check */
    if (argc != 2) {
        printf("USAGE:%s <FILE PATH>\n", argv[0]);
        return 1;

    /* get stat */
    if (stat(argv[1], &st) != 0) {
        printf("%s\n", strerror(errno));
        return 1;

    /* show */
    strftime(date_str, 255, "%Y%m%d%H%I%M%S", localtime(&st.st_mtime));
    printf("%s.%09ld\n",date_str, st.st_mtim.tv_nsec);

    return 0;

Operation check

After compiling, when you execute it, it will be displayed as follows.

$ gcc nsec_show.c  -o nsec_show
$ ./nsec_show ./nsec_show.c

By the way, it matches the nanoseconds displayed by the ls command.

$ ls ./nsec_show.c --full-time
-rw-rw-r--. 1 miyabi miyabi 581 2017-03-05 06:36:37.656058532 +0900 ./nsec_show.c



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