3.4 对于指定的描述符打印文件标志

file/fileflags.c

#include "apue.h"
#include <fcntl.h>
int
main(int argc, char *argv[])
{
	int		val;
	if (argc != 2)
		err_quit("usage: a.out <descriptor#>");
	if ((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
		err_sys("fcntl error for fd %d", atoi(argv[1]));
	switch (val & O_ACCMODE) {
	case O_RDONLY:
		printf("read only");
		break;
	case O_WRONLY:
		printf("write only");
		break;
	case O_RDWR:
		printf("read write");
		break;
	default:
		err_dump("unknown access mode");
	}
	if (val & O_APPEND)		printf(", append");
	if (val & O_NONBLOCK)	printf(", nonblocking");
#if defined(O_SYNC)
	if (val & O_SYNC)	printf(", synchronous writes");
#endif
#if !defined(_POSIX_C_SOURCE) && defined(O_FSYNC)
	if (val & O_FSYNC)	printf(", synchronous writes");
#endif
	putchar('
');
	exit(0);
}