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Thank, the cutechess code is helpful. I believe it is using Qt for some of the process stuff, perhaps there is something even smaller and more self-contained somewhere.

I am seeking simple sample code for accessing and controlling a UCI chess program (Stockfish) from C or C++ on Unix/Linux/MacOS.

I realize this code is somewhere in the big chess GUIs but I was hoping for a smaller and more self-contained example.

Ok, this one I was suspicious of and rightfully so. Unless there is some obvious immediate reason to under promote then queen should be fine. My clue was the fact that the only difference between queen and rook is the diagonal attack which is blocked by its own pawn. So I played out the winning lin...

In this position, 4q3/Pp4pk/Pp6/6P1/1p3QPP/2Pp4/b2P1pP1/K7 w - - 0 1 White wins with 1. g6+ Kh8 2. a:b7 Bg8 3. a8=R! (3. a3=Q is a fortress draw). On my machine, after 6 minutes Crystal is seeing the correct move 1. g6+ and the correct evaluation, but its principal variation is incorrect: it sees 3....

I ran the latest Crystal on a 6-CPU iMac with 6 threads and I think lots of hash (although not certain) and set to disregard the 50-move rule. It failed to give a correct evaluation of this position, which is very difficult for the engines I have tried as the key idea is pruned early: 2R2K2/p3p3/3p4...