C++/CLIによるCライブラリの.NET化

C#でSQLiteを使うには

試運転　C#からSQLiteを使う

　……さてさて、ちゃんと動いてくれるでしょうか。冒頭で示したC++によるサンプルコードをC++/CLIとC#で書いてみました。SQLite3Petiteを参照設定に加えればコンパイル/実行できるはずです。

Petite_sample_cpp.cpp

#include "stdafx.h"

using namespace System;
using namespace SQLite3Petite;

bool print_result(array<String^>^ values, array<String^>^ names) {
  for ( int i = 0; i < values->Length; ++i ) {
    System::Console::Write("{0} = [{1}] ", names[i], values[i]);
  }
  Console::WriteLine();
  return true;
}

int main() {

  Database^ db = gcnew Database();
  if ( db->open() != Result::OK ) {
    System::Console::WriteLine(
                  "Error : Can't open database : {0}", db->errmsg());
    return 1;
  }

  array<String^>^ statements = {
    L"CREATE TABLE item (id INTEGER PRIMARY KEY, 
                       name TEXT NOT NULL, price REAL NOT NULL)",
    L"INSERT INTO item VALUES ( 1, 'ばなな', 123)",
    L"INSERT INTO item VALUES ( 2, 'りんご', 234)",
    L"INSERT INTO item VALUES ( 3, 'みかん', 345)",
    L"INSERT INTO item VALUES ( 4, 'なし',   456)",
    L"INSERT INTO item VALUES ( 5, 'もも',   567)",
    L"INSERT INTO item VALUES ( 6, 'びわ',   789)",
    L"INSERT INTO item VALUES ( 7, 'くり',   891)",

    L"CREATE TABLE sales (id INTEGER PRIMARY KEY, quantity NOT NULL )",
    L"INSERT INTO sales VALUES ( 1, 6 )",
    L"INSERT INTO sales VALUES ( 3, 4 )",
    L"INSERT INTO sales VALUES ( 5, 2 )",

    L"SELECT item.id, name, price, quantity, price*quantity 
        FROM item, sales 
       WHERE item.id = sales.id ORDER BY price*quantity",

    L"CREATE VIEW named_sales AS SELECT name, quantity 
             FROM sales, item WHERE item.id = sales.id",
    L"SELECT * FROM named_sales"
  };

  for each ( String^ statement in statements ) {
    Console::WriteLine(statement);
    String^ err;
    if ( db->exec(statement, gcnew Callback(print_result), err) 
        != Result::OK ) {
      Console::WriteLine(err);
      return 1;
    }
  }

  return 0;
}

Petite_sample_cs.cs

using System;
using SQLite3Petite;

namespace Petite_sample_cs {

  class Program {

    static void Main() {
      Database db = new Database();
      if ( db.open() != Result.OK ) {
        Console.WriteLine("Error : Can't open database : {0}", 
                          db.errmsg());
        return;
      }

      string[] statements = {
        "CREATE TABLE item (id INTEGER PRIMARY KEY,
                          name TEXT NOT NULL, price REAL NOT NULL)",
        "INSERT INTO item VALUES ( 1, 'ばなな', 123)",
        "INSERT INTO item VALUES ( 2, 'りんご', 234)",
        "INSERT INTO item VALUES ( 3, 'みかん', 345)",
        "INSERT INTO item VALUES ( 4, 'なし',   456)",
        "INSERT INTO item VALUES ( 5, 'もも',   567)",
        "INSERT INTO item VALUES ( 6, 'びわ',   789)",
        "INSERT INTO item VALUES ( 7, 'くり',   891)",

        "CREATE TABLE sales (id INTEGER PRIMARY KEY, 
                             quantity NOT NULL )",
        "INSERT INTO sales VALUES ( 1, 6 )",
        "INSERT INTO sales VALUES ( 3, 4 )",
        "INSERT INTO sales VALUES ( 5, 2 )",

        "SELECT item.id, name, price, quantity, price*quantity 
           FROM item, sales 
          WHERE item.id = sales.id ORDER BY price*quantity",

        "CREATE VIEW named_sales AS SELECT name, quantity 
           FROM sales, item WHERE item.id = sales.id",
        "SELECT * FROM named_sales"
      };

      foreach ( string statement in statements ) {
        Console.WriteLine(statement);
        String err;
        if ( db.exec(statement, delegate (string[] values, 
                                          string[] names) {
               for ( int i = 0; i < values.Length; ++i ) {
                 Console.Write("{0} = [{1}] ", names[i], values[i]);
               }
               Console.WriteLine();
               return true;
             }, out err) != Result.OK ) {
            Console.WriteLine(err);
          return;
        }
      }
    }
  }

}

まとめ

　いかがでしょう、C++/CLIはnative/managed双方の仲介役として機能します。今までに書かれた大量のC/C++コードにC++/CLIで薄皮を被せて.NET化できるわけです。UIをC#やVBのWindows Formsで実装し、C/C++によるビジネスロジックをC++/CLIでUIに接続すれば（おそらくは）最小コストで従来のアプリケーションを.NET世界に組み入れることができそうです。