学步园

        The file mode, stored in the st_mode field of the file attributes,
contains two kinds of information: the file type code, and the access permission bits. This section discusses only the type code, which you can use to tell whether the file is a directory, socket, symbolic link, and so on.
For details about access permissions seePermission Bits.

        There are two ways you can access the file type information in a file mode. Firstly, for each file type there is a predicate macro which examines a given file mode and
returns whether it is of that type or not. Secondly, you can mask out the rest of the file mode to leave just the file type code, and compare this against constants for each of the supported file types.

        All of the symbols listed in this section are defined in the header file sys/stat.h. The following
predicate macros test the type of a file, given the value m which is thest_mode field returned by stat on that file:

       An alternate non-POSIX method of testing the file type is supported for compatibility with BSD. The mode can be bitwise AND-ed with S_IFMT to extract the file type code,
and compared to the appropriate constant. For example,

     S_ISCHR (mode)

is equivalent to:

     ((mode & S_IFMT) == S_IFCHR)

These are the symbolic names for the different file type codes:

S_IFDIR

This is the file type constant of a directory file. 

S_IFCHR

This is the file type constant of a character-oriented device file. 

S_IFBLK

This is the file type constant of a block-oriented device file. 

S_IFREG

This is the file type constant of a regular file. 

S_IFLNK

This is the file type constant of a symbolic link. 

S_IFSOCK

This is the file type constant of a socket. 

S_IFIFO

This is the file type constant of a FIFO or pipe.

First:

#include "apue.h"
#include "my_err.h" 

int main(int argc, char* argv[])
{
	int i;
	struct stat buf;
	char *ptr;

	for ( i = 1; i < argc; i++ )
	{
		printf("%s: ", argv[i]);
		if (lstat(argv[i], &buf) < 0 )
		{
			err_ret("lstat error", argv[i]);
			continue;
		}

		if ( S_ISREG(buf.st_mode) )
			ptr = "regular";
		else if ( S_ISDIR(buf.st_mode) )
			ptr = "direcotry";
		else if ( S_ISCHR(buf.st_mode) )
			ptr = "character special";
		else if ( S_ISBLK(buf.st_mode) )
			ptr = "block special";
		else if ( S_ISFIFO(buf.st_mode) )
			ptr = "fifo";
		else if ( S_ISLNK(buf.st_mode) )
			ptr = "symbolic link";
		else if ( S_ISSOCK(buf.st_mode) )
			ptr = "socket";
		else 
			ptr = "** unknow mode **";

		printf("%s\n", ptr);
	}
	exit(0);
}

Second:

#include "apue.h"
#include "my_err.h" 

int main(int argc, char* argv[])
{
	int i;
	struct stat buf;
	char *ptr;

	for ( i = 1; i < argc; i++ )
	{
		printf("%s: ", argv[i]);
		if (lstat(argv[i], &buf) < 0 )
		{
			err_ret("lstat error", argv[i]);
			continue;
		}

		switch (buf.st_mode & S_IFMT)
		{
		case S_IFREG: ptr = "regular"; break;
		case S_IFBLK: ptr = "block special"; break;
		case S_IFCHR: ptr = "character special"; break;
		case S_IFIFO: ptr = "fifo"; break;
		case S_IFLNK: ptr = "symbolic link"; break;
		case S_IFSOCK: ptr = "socket"; break;
		case S_IFDIR: ptr = "directory"; break;
		default:
					  ptr = "** unknow **";
		}

		printf("%s\n", ptr);
	}
	exit(0);
}