If the error queue is empty, it will return GL_NO_ERROR. Otherwise, it will return one of the error enumerators below and remove that error from the queue. So to fetch all of the errors currently in the queue, you would need to loop.
If the error queue is empty, it will return GL_NO_ERROR. Otherwise, it will return one of the error enumerators below and remove that error from the queue. So to fetch all of the errors currently in the queue, you would need to loop.