Question

I’m trying to use Mac OS X’s listxattr C function and turn it into something useful in Python. The man page tells me that the function returns a string buffer, which is a “simple NULL-terminated UTF-8 strings and are returned in arbitrary order. No extra padding is provided between names in the buffer.”

In my C file, I have it set up correctly it seems (I hope):

  char buffer[size];
  res = listxattr("/path/to/file", buffer, size, options);

But when I got to print it, I only get the FIRST attribute ONLY, which was two characters long, even though its size is 25. So then I manually set buffer[3] = ‘z’ and low and behold when I print buffer again I get the first TWO attributes.

I think I understand what is going on. The buffer is a sequence of NULL-terminated strings, and stops printing as soon as it sees a NULL character. But then how am I supposed to unpack the entire sequence into ALL of the attributes?

I’m new to C and using it to figure out the mechanics of extending Python with C, and ran into this doozy.

Answer 1

1. char *p = buffer;
2. get the length with strlen(p). If the length is 0, stop.
3. process the first chunk.
4. p = p + length + 1;
5. back to step 2.