Thread: open() and close()

Hi, all,

Here i try to open a file, close it, and then try to close it again:

Code:

int fd, result;

fd = open("myfile", O_RDONLY);
printf("file descriptor: %d\n", fd);

result = close(fd);
printf("first close: %d\n", result);

result = close(fd);
printf("second close: %d\n", result);

The outputs are:
file descriptor: 9
first close: 0
second close: 0

However as we close the file at the first time, when we close it at the second time, the result returned should be -1 which is an error number. Why it still returns 0?

Thank you!