Reducing UNDO State Size

ALERT! If you have made, or plan to make a large game, you can lose the ability to UNDO entirely! If a given game is large enough that it allows you (only) 3 or 4 undos at the outset, that number will shrink as you play the game, so that if you are 2000+ turns in, you can run out of undo completely!

This is a disturbing revelation for me, because my endgame will probably always be reached in the multiple thousands of turns, and the need for undo in the final region is almost a given!

I don’t know what to do other than post a horrifically lame message at a certain turn count in my game, telling the player that they need to start saving their game profusely because UNDO is probably not going to work any more!

@Dannii @RealNC That would be wonderful if there’s a relatively painless way to get more UNDO memory involved before my game goes public…

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Yeah, my next project I’ve just decided that I’ll have a message pop up between intense sections that says It is recommended to save your progress now.

Because it won’t really spoil anything, and there will be long challenges that could slowly steer toward failure over several turns, and UNDO simply would not be viable.


Yeah, it’s really not a matter of spoiling, I’m just afraid of disenchanting the not-negligible crowd of players that get no enjoyment from playing games where you have to save and restore. And all this time the front cover of my game has been assuring cowering players that UNDO is available…

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my current TADS WIP is geared toward merciful, and at ~720k and many major element uninplemented or just sketched (1 NPC and the thinking system barely sketched, 65% of the locs & their contents and the other NPC fully unimplemented), I have at least more than 20 or so undos (I use those for easing debug, backtracking to the alternate texts (as I noted in past, the narration relies heavily on changing perception of the environment, locs and items, the entire game being mainly a “treasure hunt of knowledge & lore”)

On the specific issue, tried to (r)grep malloc *.[ch] on Tads3’s sources ? perhaps this can give insight on the UNDO issue…

Best regards from Italy,
dott. Piergiorgio.

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The increased undo limit is now live on


Most excellent!

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@RealNC is there away to incorporate this into QTads without too much pain?

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Is there a programmatic way to determine from within a game what the available undo count is?

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