I thought the problem is inside my C++ function,but I tried this
C++ Function in C++ dll:
bool __declspec( dllexport ) OpenA(std::string file)
{
return true;
}
C# code:
[DllImport("pk2.dll")]
public static extern bool OpenA(string path);
if (OpenA(@"E:\asdasd\"))
I get an exception that the memory is corrupt,why?
If I remove the std::string parameter,it works great,but with std::string it doesnt work.
std::string and c# string are not compatible with each other. As far as I know the c# string corresponds to passing char* or wchar_t* in c++ as far as interop is concerned.
One of the reasons for this is that There can be many different implementations to std::string and c# can't assume that you're using any particular one.
Try something like this:
bool __declspec( dllexport ) OpenA(const TCHAR* pFile)
{
std::string filename(pFile);
...
return true;
}
You should also specify the appropriate character set (unicode/ansi) in your DllImport attribute.
As an aside, unrelated to your marshalling problem, one would normally pass a std:string as a const reference: const std:string& filename.
std::wstring and System.string can be compatible through below conversion:
C++ :
bool func(std::wstring str, int number)
{
BSTR tmp_str = SysAllocStringLen(str.c_str(), str.size());
VARIANT_BOOL ret = VARIANT_FALSE;
// call c# COM DLL
ptr->my_com_function(tmp_str, number, &ret);
SysFreeString(tmp_str);
return (ret != VARIANT_FALSE) ? true : false;
}
It's not possible to marshal a C++ std::string in the way you are attempting. What you really need to do here is write a wrapper function which uses a plain old const char* and converts to a std::string under the hood.
C++
extern C {
void OpenWrapper(const WCHAR* pName) {
std::string name = pName;
OpenA(name);
}
}
C#
[DllImport("pk2.dll")]
public static extern void OpenWrapper( [In] string name);
I know this topic is a tad old but for future googlers, this should also work (without using char* in C++)
C#:
public static extern bool OpenA([In, MarshalAs(UnmanagedType.LPStr)] path);
C++:
bool __declspec( dllexport ) OpenA(std::string file);
