PInvoke C++ function to use in C#

Question

i'm having an issue PInvoking a native function from c++... i have PInvoked all the other native functions without problems (params were very simple conversions). below is the c++ prototype and its usage in c++:

DECL_FOOAPIDLL DWORD WINAPI FOO_Command(
VOID *Par,  //pointer to the parameter(s) needed by the command 
DWORD Len,  //length of Parameter in bytes
DWORD Id    //identification number of the command 
);

usage:

static DWORD DoSomething(WCHAR *str)
{
DWORD len = (wcslen(str)+1)*sizeof(WCHAR);
DWORD ret = FOO_Command((VOID *)str,len,FOOAPI_COMMAND_CLOSE);
return(ret);
}

my C# PInvoke:

[DllImport("FOO.dll")]
    static public extern uint FOO_Command(IntPtr par, uint len, uint id);

private void DoSomething()
{

    string text = "this is a test";
    IntPtr ptr = Marshal.StringToHGlobalUni(text);

    uint hr = FOO_Command(ptr,255, FOOAPI_COMMAND_CLOSE);

    Marshal.FreeHGlobal(ptr);

}

1) is this the correct way to PInvoke this API? 2) how can i get the size of ptr where i have 255 as the parm?

the above does work, but i'm new to PInvoke and the "Native" world...

Thank you

Answer 1

private void DoSomething() 
{ 

    string text = "this is a test"; 
    IntPtr ptr = Marshal.StringToHGlobalUni(text); 

    uint hr = FOO_Command(ptr, (text.Length + 1) * 2, FOOAPI_COMMAND_CLOSE); 

    Marshal.FreeHGlobal(ptr); 

}