Linux 下stat和access函数

1.stat既有命令也有同名函数，用来获取文件Inode里主要信息（即文件类型、文件权限、创建/修改/访问时间等就是ls -l看到的相关的信息），stat 跟踪符号链接，lstat不跟踪符号链接。可以通过man 2 stat查看相关的信息。

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>

int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);

struct stat {
               dev_t     st_dev;     /* ID of device containing file */
               ino_t     st_ino;     /* inode number */
               mode_t    st_mode;    /* protection */
               nlink_t   st_nlink;   /* number of hard links */
               uid_t     st_uid;     /* user ID of owner */
               gid_t     st_gid;     /* group ID of owner */
               dev_t     st_rdev;    /* device ID (if special file) */
               off_t     st_size;    /* total size, in bytes */
               blksize_t st_blksize; /* blocksize for filesystem I/O */
               blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
               time_t    st_atime;   /* time of last access */
               time_t    st_mtime;   /* time of last modification */ //指的是修改文件内容
               time_t    st_ctime;   /* time of last status change */ //指的是修改inode属性
            };

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

int main(int argc, char *argv[])
{
	struct stat filestat;
	if (argc < 2)
	{
		printf("Usage: %s <pathname>\n", argv[0]);
		return 0;
	}
	if (stat(argv[1], &filestat) == -1)
	{
		perror("stat error:");
		return 0;
	}

	printf("File type:                ");

	switch (filestat.st_mode & S_IFMT)// 0170000   bit mask for the file type bit fields
	{
	case S_IFBLK:
		printf("block device\n");
		break;
	case S_IFCHR:
		printf("character device\n");
		break;
	case S_IFDIR:
		printf("directory\n");
		break;
	case S_IFIFO:
		printf("FIFO/pipe\n");
		break;
	case S_IFLNK:
		printf("symlink\n");
		break;
	case S_IFREG:
		printf("regular file\n");
		break;
	case S_IFSOCK:
		printf("socket\n");
		break;
	default:
		printf("unknown?\n");
		break;
	}

	printf("I-node number:            %ld\n", (long) filestat.st_ino);

	printf("Mode:                     %lo (octal)\n",
			(unsigned long) filestat.st_mode);

	printf("Link count:               %ld\n", (long) filestat.st_nlink);
	printf("Ownership:                UID=%ld   GID=%ld\n", (long) filestat.st_uid,
			(long) filestat.st_gid);

	printf("Preferred I/O block size: %ld bytes\n", (long) filestat.st_blksize);
	printf("File size:                %lld bytes\n", (long long) filestat.st_size);
	printf("Blocks allocated:         %lld\n", (long long) filestat.st_blocks);

	printf("Last status change:       %s", ctime(&filestat.st_ctime));
	printf("Last file access:         %s", ctime(&filestat.st_atime));
	printf("Last file modification:   %s", ctime(&filestat.st_mtime));

	return 0;
}

2.access函数

功 能: 确定文件或文件夹的访问权限。即，检查某个文件的存取方式，比如说是只读方式、只写方式等。如果指定的存取方式有效，则函数返回0，否则函数返回-1。

#include <unistd.h>
int access(const char *pathname, int mode);

按实际用户ID和实际组ID测试,跟踪符号链接

参数mode

R_OK 是否有读权限

W_OK 是否有写权限

X_OK 是否有执行权限

F_OK 测试一个文件是否存在

#include<stdio.h>
#include<unistd.h>

int main(int argc, char *argv[])
{
	if (argc < 2)
	{
		printf("Usage: %s <pathname>\n", argv[0]);
		return 0;
	}
	if(access(argv[1],R_OK|X_OK|W_OK)==0)
	{
		printf("read wirte execute \n");
	}
	return 0;
}

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