Why do you need to know the next value? Personally, I wouldn't rely upon the next value of an auto increment value. What value comes next is vendor specific.
For example, lets say you have a new table and add 5 records in it. Then, you delete the 3rd record. At this point, I believe the auto increment is at 6. But, if you shut down the server, mySQL will point at 3 as the auto increment value.
Now what did that buy you? What was the benefit of knowing if auto increment was at 3 or 6? If your application depends on the incrementing of a proprietary database algorithm to create identifier keys, you are asking for trouble, in my opinion.
And what if mySQL AB changes the auto increment behaivior behind the scenes. Your application would go haywire.
Further, if you had to port your mySQL database over to another vendor your existing code would break.
Trying to take control over auto increment is playing with fire. If you want control (like create invoice numbers), roll your own invoice number table by having a column in it that keeps a counter that never reuses numbers - just choose a very large integral type (like a 32-bit unsigned long). That way, the invoice number has a specific meaning to the application that you control, rather than trying to outguess the database server.
