exprtk_simple_example_08.cpp

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/*
 **************************************************************
 *         C++ Mathematical Expression Toolkit Library        *
 *                                                            *
 * Simple Example 08                                          *
 * Author: Arash Partow (1999-2025)                           *
 * URL: https://www.partow.net/programming/exprtk/index.html  *
 *                                                            *
 * Copyright notice:                                          *
 * Free use of the Mathematical Expression Toolkit Library is *
 * permitted under the guidelines and in accordance with the  *
 * most current version of the MIT License.                   *
 * https://www.opensource.org/licenses/MIT                    *
 * SPDX-License-Identifier: MIT                               *
 *                                                            *
 **************************************************************
*/
 
 
#include <cstdio>
#include <string>
 
#include "exprtk.hpp"
 
 
template <typename T>
void composite()
{
   typedef exprtk::symbol_table<T>         symbol_table_t;
   typedef exprtk::expression<T>           expression_t;
   typedef exprtk::parser<T>               parser_t;
   typedef exprtk::parser_error::type      err_t;
   typedef exprtk::function_compositor<T>  compositor_t;
   typedef typename compositor_t::function function_t;
 
   T x = T(1);
   T y = T(2);
 
   compositor_t compositor;
 
   symbol_table_t& symbol_table = compositor.symbol_table();
   symbol_table.add_constants();
   symbol_table.add_variable("x",x);
   symbol_table.add_variable("y",y);
 
   compositor.add(
      function_t("f")     // f(x) = sin(x / pi)
      .var("x")
      .expression( "sin(x / pi)" ));
 
   compositor.add(
      function_t("g")     // g(x,y) = 3[f(x) + f(y)]
      .vars("x", "y")
      .expression( "3*[f(x) + f(y)]" ));
 
   std::string expression_string = "g(1 + f(x), f(y) / 2)";
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
 
   if (!parser.compile(expression_string,expression))
   {
      printf("Error: %s\tExpression: %s\n",
             parser.error().c_str(),
             expression_string.c_str());
 
      for (std::size_t i = 0; i < parser.error_count(); ++i)
      {
         const err_t error = parser.get_error(i);
 
         printf("Error: %02d  Position: %02d Type: [%14s] Msg: %s\tExpression: %s\n",
                static_cast<unsigned int>(i),
                static_cast<unsigned int>(error.token.position),
                exprtk::parser_error::to_str(error.mode).c_str(),
                error.diagnostic.c_str(),
                expression_string.c_str());
      }
 
      return;
   }
 
   const T result = expression.value();
 
   printf("%s = %e\n", expression_string.c_str(), result);
}
 
int main()
{
   composite<double>();
   return 0;
}