As a convenience, you can use the function XkbOpenDisplay to perform these three tasks at once: open a connection to an X server, check for a compatible version of the Xkb extension in both the library and the server, and initialize the extension for use.
XkbOpenDisplay is a convenience function that opens an X display connection and initializes the X keyboard extension. In all cases, upon return reason_rtrn contains a status value indicating success or the type of failure. If major_in_out and minor_in_out are not NULL, XkbOpenDisplay first calls XkbLibraryVersion to determine whether the client library is compatible, passing it the values pointed to by major_in_out and minor_in_out. If the library is incompatible, XkbOpenDisplay backfills major_in_out and minor_in_out with the major and minor extension versions of the library being used and returns NULL. If the library is compatible, XkbOpenDisplay next calls XOpenDisplay with the display_name. If this fails, the function returns NULL. If successful, XkbOpenDisplay calls XkbQueryExtension and backfills the major and minor Xkb server extension version numbers in major_in_out and minor_in_out. If the server extension version is not compatible with the library extension version or if the server extension is not present, XkbOpenDisplay closes the display and returns NULL. When successful, the function returns the display connection.
The possible values for reason_rtrn are:
The XkbOpenDisplay function returns NULL if the call to XOpenDisplay with the display_name fails.
The XkbOpenDisplay function returns NULL and closes the display if the server extension version is not compatible with the library extension version or if the server extension is not present.