How to: Modify System::String in Native Function Using PInvoke
Visual Studio 2005
You can pass an array of String to a native function and modify the array in the native function using PInvoke services with DllImportAttribute and MarshalAsAttribute.
Example
Compile the native library.
// string_in_native_function.cpp
// compile with: /LD
#include <stdio.h>
#include <windows.h>
extern "C" {
__declspec(dllexport) int f(wchar_t* buff[]) {
printf_s("in f: %S\n", buff[0]);
fflush(stdin);
fflush(stdout);
buff[0] = L"changed";
return wcslen(buff[0]);
}
};
Compile the following assembly that consumes the native DLL.
// string_in_native_function_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Runtime::InteropServices;
[DllImport("string_in_native_function.dll", CharSet=CharSet::Unicode)]
int f([In][Out][MarshalAsAttribute(UnmanagedType::LPArray,
ArraySubType=UnmanagedType::LPWStr, SizeConst=2)] array<String ^> ^ str);
int main() {
array<String ^> ^ myarr = gcnew array<String^>(2);
myarr[0] = "one";
myarr[1] = "two";
f(myarr); // call to imported native function.
Console::WriteLine("in managed: {0}", myarr[0]);
}
Output
in f: one in managed: changed
