How to port C++ code and DLL to C#

I don't believe that C# has the capacity to automatically understand what a string type is in C++, it's natively unable to convert a C# string into a C++ std::string or otherwise.

Instead of using base::string& as the last parameter consider using char* instead, and then assign the value within the method. Alternatively you can use a StringBuilder so that the C++ method can write to the value.

For example:

// C++
VIXHZ_EXPORT long _VixHz_LoginDevice(char *szIp, int nPort, char* szUserName, char* szPassword, char* strOutInfo, int strOutInfoLength);

// C#
[DllImport(dll)]
public static extern long _VixHz_LoginDevice(string szIp, int nPort, string szUserName, string szPassword, StringBuilder strOutInfo, int strOutInfoLength);

// Call
StringBuilder strOut = new StringBuilder(32);
_VixHz_LoginDevice("1.2.3.4", 1234, "username", "password", strOutInfo, strOutInfo.Capacity);

You can omit the length parameter if you know exactly what the maximum length is expecting to be and the C++ isn't going to exceed it. An example with the StringBuilder can be found here:

Default Marshaling for Strings | Microsoft Docs[^]