exprtk_simple_example_18.cpp

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/*
 **************************************************************
 *         C++ Mathematical Expression Toolkit Library        *
 *                                                            *
 * Simple Example 18                                          *
 * 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 file_io()
{
   typedef exprtk::symbol_table<T> symbol_table_t;
   typedef exprtk::expression<T>   expression_t;
   typedef exprtk::parser<T>       parser_t;
 
   const std::string fileio_program =
      " var file_name := 'file.txt';                          "
      " var stream    := null;                                "
      "                                                       "
      " if (stream := open(file_name,'w'))                    "
      "    println('Successfully opened file: ' + file_name); "
      " else                                                  "
      " {                                                     "
      "    println('Failed to open file: ' + file_name);      "
      "    return [false];                                    "
      " };                                                    "
      "                                                       "
      " var s := 'Hello world...\n';                          "
      "                                                       "
      " for (var i := 0; i < 10; i += 1)                      "
      " {                                                     "
      "    write(stream,s);                                   "
      " };                                                    "
      "                                                       "
      " if (close(stream))                                    "
      "    println('Sucessfully closed file: ' + file_name);  "
      " else                                                  "
      " {                                                     "
      "    println('Failed to close file: ' + file_name);     "
      "    return [false];                                    "
      " }                                                     ";
 
   exprtk::rtl::io::file::package<T> fileio_package;
   exprtk::rtl::io::println<T>       println;
 
   symbol_table_t symbol_table;
   symbol_table.add_function("println",println);
   symbol_table.add_package (fileio_package   );
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
   parser.compile(fileio_program,expression);
 
   printf("Result %10.3f\n",expression.value());
}
 
int main()
{
   file_io<double>();
   return 0;
}