C++ Mathematical Expression Library (ExprTk) http://www.partow.net/programming/exprtk/index.html

exprtk.hpp

@@ -9978,6 +9978,9 @@ namespace exprtk
          lexer::token token;
          error_mode mode;
          std::string diagnostic;
+         std::string error_line;
+         std::size_t line_no;
+         std::size_t column_no;
       };
 
       inline type make_error(error_mode mode, const std::string& diagnostic = "")
@@ -9986,6 +9989,8 @@ namespace exprtk
          t.mode       = mode;
          t.token.type = lexer::token::e_error;
          t.diagnostic = diagnostic;
+         t.line_no    = 0;
+         t.column_no  = 0;
          return t;
       }
 
@@ -10013,6 +10018,45 @@ namespace exprtk
          }
       }
 
+      bool update_error(type& error, const std::string& expression)
+      {
+         if (
+              expression.empty()                                               ||
+              (error.token.position >= expression.size())                      ||
+              (std::numeric_limits<std::size_t>::max() == error.token.position)
+            )
+         {
+            return false;
+         }
+
+         std::size_t error_line_start = 0;
+         for (std::size_t i = error.token.position; i > 0; --i)
+         {
+            if ('\n' == expression[i])
+            {
+               error_line_start = i;
+               break;
+            }
+         }
+
+         std::size_t next_nl_position = std::min(expression.size(),
+                                                 expression.find_first_of('\n',error.token.position + 1));
+
+         error.column_no  = error.token.position - error_line_start;
+         error.error_line = expression.substr(error_line_start,
+                                              next_nl_position - error_line_start);
+
+         error.line_no = 0;
+
+         for (std::size_t i = 0; i < next_nl_position; ++i)
+         {
+            if ('\n' == expression[i])
+               ++error.line_no;
+         }
+
+         return true;
+      }
+
       inline void dump_error(const type& error)
       {
          printf("Position: %02d   Type: [%s]   Msg: %s\n",
@@ -10289,12 +10333,16 @@ namespace exprtk
          {
             set_error(
                make_error(parser_error::e_syntax,
-                          "ERR02 - Incomplete expression!"));
+                          current_token_,
+                          "ERR02 - Incomplete expression due to unexpected token: '" + current_token_.value + "'"));
+
             symbol_name_cache_.clear();
+
             if (0 != e)
             {
                delete e;
             }
+
             return false;
          }
       }