程序员修炼之道读书笔记 24 code generator 实现

Exercises 13.
Write a code generator that takes the input file in
Figure 3.4, and generates output in two languages of
your choice. Try to make it easy to add new languages

下面是C++ 实现，只对例题中给出的例子有效，很多代码时hard code，如果要更generic 实现，可以修改实现。 由此可以如果是使用Python 或perl 脚本实现会容易的多，C++，C需要考虑过多的细节，不太适合文本操作，过于复杂。

-bash-4.2$ cat codeGenerator.cpp

// This cpp file is used to generate source code for C and Pascal automatically

#include<iostream>

#include<string>

#include<string.h>

#include <fstream>

using namespace std;

string getElementN(string &str, int n) {

  //assert(n >= 0 && n <=4);

  string strWords[5];

  int counter = 0;

  for(short i=0;i<str.length();i++){

      if(str[i] == ' '){

          counter++;

          i++;

      }

      if (str[i] != ' ')

        strWords[counter] += str[i];

  }

  return strWords[n];

}

void CGenerator() {

  string line;

  ifstream fin ("msg.def");

  ofstream fout ("msg.c");

  if (fin.is_open() && fout.is_open())

  {

    string structName;

    string charArray;

    while ( getline (fin,line) )

    {

      switch ((char)line[0]) {

        case 'M':

          fout << "typedef struct {" << '\n';

          structName = line.substr(2);

          break;

        case 'F':

          charArray = getElementN(line, 2);

          if (charArray.substr(0,3) == "char")

            fout << "  char " << getElementN(line, 1) << charArray.substr(4) << ";" << '\n';

          else

            fout << "  " << getElementN(line, 2) << " " << getElementN(line, 1) << ";"  << '\n';

          break;

        case 'E':

          fout << "} " << structName << ";" <<  '\n';

          break;

        default:

           cerr << "Unsupported type! " << endl;

           break;

      }

    }

    fin.close();

    fout.close();

  }

  else cout << "Unable to open file";

}

void PascalGCenerator() {}

int main(void) {

  CGenerator();

  //PascalGenerator(); //Similarly, you can implement PascalGeneator

  return 0;

}

Input file:

-bash-4.2$ cat msg.def

M AddProduct

F id  int

F name  char[30]

F order_code int

E

Generated file:

-bash-4.2$ cat msg.c

typedef struct {

  int id;

  char[30] name;

  int order_code;

} AddProduct;