equivalent char* in C#

Question

I have a dll that is written in c++. And I am p/invoking to call the functions.

I have this c++ declaration.

int dll_registerAccount(char* username,          


        

Answer 1

The C# way of doing this is by letting the marshaler handle the char* stuff while you work with a string:

[DllImport("pjsipDlld")]
static extern int dll_registerAccount(
    [MarshalAs(UnmanagedType.LPStr)]string username,
    [MarshalAs(UnmanagedType.LPStr)]string password);

Replace LPStr with LPWStr if you're working with wide chars.

Answer 2

StringBuilder for char*, since the length is unknown?

[DllImport("pjsipDlld")]
static extern int dll_registerAccount(StringBuilder username, StringBuilder password);

Answer 3

Be aware of calling conventions, this tripped me up. In my case I need to call a C++ DLL but with C-style exports, which uses the cdecl calling convention. If you have the luxury of having the source Visual Studio Solution, go to Properties -> C/C++ -> Advanced and find it under "Calling Convention". This fix it for me:

[DllImport(DllName, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
// bool MyFunction(char* fileName) <-- From the DLL
static extern bool MyFunction(string fileName);

Answer 4

    [DllImport("pjsipDlld", CharSet = CharSet.Ansi)]
    static extern int dll_registerAccount(string username, string password);

Answer 5

[DllImport("DLL loction"), EntryPoint = "dll_registerAccount",
    CallingConvention = CallingConvention.Cdecl)]
[return : MarshalAs(UnmanagedType.I4)]
static extern int dll_registerAccount(
    [MarshalAs(UnmanagedType.LPStr)]string username,
    [MarshalAs(UnmanagedType.LPStr)]string password);

• cdecl is the default calling convention for C and C++ programs,
• refer these doc for more information.