If xcb_connect() fails, it doesn't return NULL. Instead, it always
returns an xcb_connection_t*, and the user should check for errors with
the xcb_connection_has_error() function. What this function does is
check if conn->has_error contains a non-zero error code, and returns it.
If an error did occur, xcb doesn't actually return a full
xcb_connection_t though, it just returns (xcb_connection_t *)
error_code. Since the 'has_error' field is the first, it is still
possible to check conn->has_error.
That last trick was not immediately obvious to me, so add some guiding
comments. This also ensures no one obliviously rearranges the struct.
Signed-off-by: Ran Benita <ran234@gmail.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>
/* Return connection error state.
* To make thread-safe, I need a seperate static
* variable for every possible error.
+ * has_error is the first field in xcb_connection_t, so just
+ * return a casted int here; checking has_error (and only
+ * has_error) will be safe.
*/
xcb_connection_t *_xcb_conn_ret_error(int err)
{
/* xcb_conn.c */
struct xcb_connection_t {
+ /* This must be the first field; see _xcb_conn_ret_error(). */
int has_error;
/* constant data */