.NET Marshalling

Interesting things happen when you try to marshal something in real life….Even if you do not happen to dig into strange structure-marshalling: just a few methods or smth. strange problems may occur. For example marshalling char** for in and out usage. I was struggling for about a day for the code worked on developmnet environment and did not on test:). So the correct marshal is next [native]

extern __declspec(dllexport) int SomeFunc(char** stringArray);

[marshal]

[DllImport("funct.dll", EntryPoint = "SomeFunc", ExactSpelling = true)]
internal static extern int SomeFunc([In,Out] String[] stringArray);

AND! Do not forget to allocate enough memory for the array elements:

[pseudocode]

for (int i = 0; i <> {
           arr[i] = new String(' ', 256);
}

If you want to marshal a string and DO NOT use it afterwards(no result is written to it) use string but if you do use a StringBuilder with OUT modifier: [native]

extern __declspec(dllexport) int SomeFunc(void* ad, char* buf, int size, float someParam);

[marshal]

[DllImport("funct.dll", EntryPoint = "SomeFunc", ExactSpelling = true)]
internal static extern int SomeFunc(IntPtr handle, [Out] StringBuilder buffer, int size, [In] float someParam);

Now let us imagine a more complicated example of function: two string are passed to the function: one is an ASCII string and one is a UNICODE one. The result has to be written into the second string. simple auto modifier in CharSet wont help we’ll have to use MarshalAs attribute: [native]

extern __declspec(dllexport) int SomeFunc(void* ad, const char *name, wchar_t *value, int valueSize);

[marshal]

[DllImport("funct.dll", EntryPoint = "SomeFunc",CharSet=CharSet.Auto, ExactSpelling = true)]
internal static extern int SomeFunc(IntPtr handle, [MarshalAs(UnmanagedType.LPStr)] [In] string name, [MarshalAs(UnmanagedType.LPWStr)] [In,Out] string value, int size);