xcb_request_check

@brief Return the error for a request, or NULL if none can ever arrive. @param c: The connection to the X server. @param cookie: The request cookie. @return The error for the request, or NULL if none can ever arrive.

The xcb_void_cookie_t cookie supplied to this function must have resulted from a call to xcb_request_name_checked(). This function will block until one of two conditions happens. If an error is received, it will be returned. If a reply to a subsequent request has already arrived, no error can arrive for this request, so this function will return NULL.

Note that this function will perform a sync if needed to ensure that the sequence number will advance beyond that provided in cookie; this is a convenience to avoid races in determining whether the sync is needed.

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