一、用read函数完成文件大小计算

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, const char *argv[])
{
	int fd = open("./1.txt",O_RDONLY);
	if(fd < 0)
	{
		perror("open");
		return -1;
	}
	printf("open success!\n");

	off_t size = lseek(fd,0,SEEK_END);
	printf("size=%ld\n",size);

	char c;
	ssize_t res = 0;
	int count = 0;
	lseek(fd,0,SEEK_SET);
	while(1)
	{
		res = read(fd,&c,1);
		if(0 == res)
			break;
		count++;
	}
	printf("count=%d\n",count);

	if(close(fd) < 0)
	{
		perror("close");
		return -1;
	} 
	printf("close success!\n");
	return 0;
}

二、将文件权限提取修改成循环方式

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
void get_filePermission(mode_t m)
{
	long x = 0400;
	char c[]="rwx";
	int count = 0; 
	while(x)
	{
		if((m & x) == 0)
			putchar('-');
		else
			printf("%c",c[count%3]);
		count++;
		x = x >> 1;
	}
	putchar(' ');
}
int main(int argc, const char *argv[])
{
	struct stat buf;
	if(stat("./1.txt",&buf) < 0)
	{
		perror("stat");
		return -1;
	}

	printf("0%o ",buf.st_mode);
	get_filePermission(buf.st_mode);
	printf("%ld ",buf.st_nlink);
	printf("%d ",buf.st_uid);
	printf("%d ",buf.st_gid);
	printf("%ld ",buf.st_size);
	struct tm *info=NULL;
	info = localtime(&buf.st_mtime);
//	printf("%ld ",buf.st_ctime);
	printf("%d-%02d-%02d %02d:%02d:%02d\n",info->tm_year+1900,info->tm_mon+1,info->tm_mday,info->tm_hour,info->tm_min,info->tm_sec);
	return 0;
}