Improve error message on missing net.

small rewording, but also print the download url for the default net.

closes https://github.com/official-stockfish/Stockfish/pull/2954

No functional change

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 1ae6cb3ac56f88d91ca8d56be259505d2a5f35e5..a642357e3c4904ea0ff5f6160325cd51d52b8b59 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -50,9 +50,13 @@ namespace Eval {
     std::string eval_file = std::string(Options["EvalFile"]);
     if (useNNUE && eval_file_loaded != eval_file)
     {
     std::string eval_file = std::string(Options["EvalFile"]);
     if (useNNUE && eval_file_loaded != eval_file)
     {

-        std::cerr << "Use of NNUE evaluation, but the file " << eval_file << " was not loaded successfully. "
-                  << "These network evaluation parameters must be available, compatible with this version of the code. "
-                  << "The UCI option EvalFile might need to specify the full path, including the directory/folder name, to the file." << std::endl;
+        UCI::OptionsMap defaults;
+        UCI::init(defaults);
+
+        std::cerr << "NNUE evaluation used, but the network file " << eval_file << " was not loaded successfully. "
+                  << "These network evaluation parameters must be available, and compatible with this version of the code. "
+                  << "The UCI option EvalFile might need to specify the full path, including the directory/folder name, to the file. "
+                  << "The default net can be downloaded from: https://tests.stockfishchess.org/api/nn/"+std::string(defaults["EvalFile"]) << std::endl;

         std::exit(EXIT_FAILURE);
     }
 
         std::exit(EXIT_FAILURE);
     }