用c#中的char*调用一个c++函数

Question

我有一个CLR C++dll，它重写了一个静态C++库。我有以下课程：

#pragma once
#include <windows.h>
#include <sddl.h>
#include <LibEx.h>
using namespace System;
#using <mscorlib.dll>
namespace LIB_WrapperNamespace {
    public ref class LIB_WrapperClass
    {
    public:
        BOOL WINAPI T_LibEx_ConsoleConnect(IN DWORD num1, IN LPWSTR Name)
        {
            return LibEx_ConsoleConnect(num1,Name);
        }
        };
} 

在C#中，我添加了对库的引用

LIB_WrapperNamespace.LIB_WrapperClass myLib = new LIB_WrapperNamespace.LIB_WrapperClass();

现在如何调用这个函数，如何将字符串发送到char*？来自C#：

string myName = "NAME";
myLib.T_LibEx_ConsoleConnect(1,**myName**);

Answer 1

API应该将该参数公开为wchar_t*，因此您需要在C#中提供一个指针值。尝试以下

IntPtr ptr = IntPtr.Zero;
try { 
  ptr = Marshal.StringToCoTaskMemUni("NAME");
  unsafe { 
    myLib.T_LibEx_Consoleconnect(1, (char*)(ptr.ToPointer()));
  }
} finally { 
  if (ptr != IntPtr.Zero) { 
    Marshal.FreeCoTaskMem(ptr);
  }
}

不幸的是，由于您已经使用原始指针值公开了该方法，因此如果没有unsafe代码，就无法从C#中使用该方法。另一种方法是暴露过载，比如string^。这在C#中是可用的，并且C++/CLI代码可以处理从string^到LPWSTR 的编组

BOOL WINAPI T_LibEx_ConsoleConnect(DWORD num1, String^ Name) { 
   IntPtr ip = Marshal::StringToHGlobalUni(Name);
   BOOL ret = T_LibEx_ConsoleConnect(num1, static_cast<LPWSTR>(ip.ToPointer()));
   Marshal::FreeHGlobal(ip);
   return ret;
}
// From C#
myLib.T_LibEx_ConsoleConnect(1, "NAME");

Answer 2

当您将封送处理问题"暴露"给包装器的用户时，为什么要构建C++\CLI项目来包装某些内容？C++\CLI的思想是将封送处理问题隐藏在包装器中。您应该为.NET:原生地声明函数

#pragma once
#include <Windows.h>
#include <stdlib.h>
#include <string.h>
#include <msclrmarshal_cppstd.h> 
#include <vector>
namespace ClassLibrary2 {
public ref class Class1
{
public:
    //Expose .NET types to .NET users.
    System::Boolean T_LibEx_ConsoleConnect(System::UInt64 num1, System::String^ Name);
};

}

当你觉得合适的时候，实现这个包装器函数，它可能看起来像这样：

#include "ClassLibrary2.h"
namespace ClassLibrary2 {
System::Boolean Class1::T_LibEx_ConsoleConnect(
    System::UInt64 num1, 
    System::String^ Name)
{
    //Initialize marshaling infrastructure. You can use its instance many times 
    //through out life span of your application.
    msclr::interop::marshal_context^ marshalContext = gcnew msclr::interop::marshal_context();
    //Turn System::String into LPWSTR. Keep in mind that you are now the owner of 
    //memory buffer allocated for unmanagedName. You need to release it somewhere.
    const wchar_t* clsConstChars = marshalContext->marshal_as<const wchar_t*>(Name);
    LPWSTR unmanagedName = const_cast<LPWSTR>(clsConstChars);
    //System::UInt64 num1 will be marshalled to DWORD natively by compiler.
    return LibEx_ConsoleConnect(num1, unmanagedName);
}}