issue doxygen#11849 Incorrect evaluation of __VA_OPT__ when preprocessing

Author: doxygen

src/doxygen.cpp

@@ -10180,7 +10180,7 @@ static void runQHelpGenerator()
       static const reg::Ex versionReg(R"(Qt (\d+)\.(\d+)\.(\d+))");
       reg::Match match;
       std::string s = inBuf;
-      if (reg::search(inBuf,match,versionReg))
+      if (reg::search(s,match,versionReg))
       {
         qtVersion = 10000*QCString(match[1].str()).toInt() +
                       100*QCString(match[2].str()).toInt() +

src/pre.l

@@ -3052,7 +3052,8 @@ static bool expandExpression(yyscan_t yyscanner,QCString &expr,QCString *rest,in
           // expr='( something __VA_OPT__(value) )' or '( something __VA_OPT__(value) something_else )'
           static const reg::Ex re(R"(__VA_OPT__\((.*)\)(.*)\))");
           reg::Match m;
-          if (reg::search(expr.mid(p).str(),m,re))
+          std::string s = expr.mid(p).str();
+          if (reg::search(s,m,re))
           {
             assert(m.size()==3);
             std::string value     = m[1].str();