ReadFile

[John E]

Igor, I tried your suggestion and it works fine - as long as 'handle' is within the range of low-level (POSIX style) handle numbers. Here's the code from libTIFF:-

static tsize_t
_tiffReadProc(thandle_t fd, tdata_t buf, tsize_t size)
{
	DWORD dwSizeRead;

	if (!ReadFile(fd, buf, size, &dwSizeRead, NULL))
		return(0);
	return ((tsize_t) dwSizeRead);
}

If the file was opened by libTIFF itself, 'fd' will already be a valid WinOS file handle (a long). In my case however, it can also be opened by libgdk_pixbuf in which case, it'll be a low-level, POSIX style handle (an int). For obvious reasons, the above function can't tell one from the other.

Assuming that the values would never overlap (which may or may not be a safe assumption) I could get around this problem by testing to see if 'fd' was already within the range of known WinOS values or alternatively, if it was in the range of low-level values.

At first, I hoped that a simple numerical test would suffice. But when I tried your code this morning, the value returned by _get_osfhandle() was worryingly close the the value I passed in. Can you think of any other way I could test the validity of 'fd'?