C++の資源をDLLを介してC#から使う(メモ)

概要

C++ 側と c# 側とで可変長文字列をやり取りする際のメモリの扱いが異なり、癖があるのでメモ。

C++ 側に文字列を引数で渡し、【戻り値】で受け取る方法

DllTest.cs(C#)

[TestClass]
public class DllTest
{
    [DllImport("MyDLL.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
    [return: MarshalAs(UnmanagedType.LPStr)]
    static extern string DllTestMethod(string hoge);

    [TestMethod]
    public void CanPassAndReceiveStringToDll()
    {
        string output = DllTestMethod("ああ");
        Assert.AreEqual("ああてすと", output);
    }
}

API.h(C++)

#pragma once

#define DllExport __declspec( dllexport )

extern "C"
{
    DllExport int __stdcall DllTestMethod(char* hoge);
}

API.cpp(C++)

#include "stdafx.h"
#include <iostream>
#include "API.h"


char* CStringToChar(LPCWSTR pStr) {
    // 変換後に必要なメモリサイズ取得
    int iByte = WideCharToMultiByte(CP_ACP, 0, pStr, -1, NULL, 0, NULL, NULL);

    // 文字列格納領域確保
    char* pszReturn = (char*)::CoTaskMemAlloc(iByte);

    // 変換
    WideCharToMultiByte(CP_ACP, 0, pStr, -1, pszReturn, iByte, NULL, NULL);

    return pszReturn;
}


char* CStringToChar(CString str) {
    // 変換元取得
    LPCWSTR pStr = str.GetString();
    return CStringToChar(pStr);
}


char* __stdcall DllTestMethod(char* hoge)
{
    std::cout << "Call C DLL!! - [" << hoge << "]" << std::endl;
    return CStringToChar(CString(hoge) + _T("てすと"));
}

C++ 側に文字列を引数で渡し、【引数】で受け取る方法

DllTest.cs(C#)

[TestClass]
public class DllTest
{
    [DllImport("MyDLL.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
    static extern int DllTestMethod(string hoge, [MarshalAs(UnmanagedType.LPStr), Out] out string output);

    [TestMethod]
    public void CanPassAndReceiveStringViaDll()
    {
        int res = CanPassAndReceiveStringToDll("ああ", out string output);
        Assert.AreEqual(res, 123);
        Assert.AreEqual(output, "ああてすと");
    }
}

API.h(C++)

#pragma once

#define DllExport __declspec( dllexport )

extern "C"
{
    DllExport int __stdcall DllTestMethod(char* hoge, const char** output);
}

API.cpp(C++)

#include "stdafx.h"
#include <iostream>
#include "API.h"


char* CStringToChar(LPCWSTR pStr) {
    // 変換後に必要なメモリサイズ取得
    int iByte = WideCharToMultiByte(CP_ACP, 0, pStr, -1, NULL, 0, NULL, NULL);

    // 文字列格納領域確保
    char* pszReturn = (char*)::CoTaskMemAlloc(iByte);

    // 変換
    WideCharToMultiByte(CP_ACP, 0, pStr, -1, pszReturn, iByte, NULL, NULL);

    return pszReturn;
}


char* CStringToChar(CString str) {
    // 変換元取得
    LPCWSTR pStr = str.GetString();
    return CStringToChar(pStr);
}


int __stdcall DllTestMethod(char* hoge, const char** output)
{
    std::cout << "Call C DLL!! - [" << hoge << "]" << std::endl;
    *output = CStringToChar(CString(hoge) + _T("てすと"));
    return 123;
}