Short script to query a size of a file by open and seek.

filesz.c

#define _GNU_SOURCE // Needed to use O_LARGEFILE and lseek64

#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	int fd;
	off64_t sz;

	if (argc != 2) {
		fprintf(stderr, "Usage: ./filesz FILE\n");
		return -1;
	}


	fd = open(argv[1], O_RDONLY | O_LARGEFILE);
	if (fd < 0) {
		fprintf(stderr, "Err: open ret(%d) (%s)\n", fd, strerror(errno));
		return -1;
	}

	sz = lseek64(fd, 0, SEEK_END);
	if (sz < 0) {
		fprintf(stderr, "Err: lseek ret(%lld) (%s)\n", sz, strerror(errno));
		return -1;
	}

	printf("File size : %lld (0x%llx)\n", sz, sz);

	return 0;
}