How to: Modify Reference Class in a Native Function
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The latest version of this topic can be found at How to: Modify Reference Class in a Native Function.
You can pass a reference class with a CLR array to a native function, and modify the class, using PInvoke services.
Example
Compile the following native library.
// modify_ref_class_in_native_function.cpp
// compile with: /LD
#include <stdio.h>
#include <windows.h>
struct S {
wchar_t* str;
int intarr[2];
};
extern "C" {
__declspec(dllexport) int bar(S* param) {
printf_s("str: %S\n", param->str);
fflush(stdin);
fflush(stdout);
printf_s("In native: intarr: %d, %d\n",
param->intarr[0], param->intarr[1]);
fflush(stdin);
fflush(stdout);
param->intarr[0]=300;param->intarr[1]=400;
return 0;
}
};
Example
Compile the following assembly.
// modify_ref_class_in_native_function_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Runtime::InteropServices;
[StructLayout(LayoutKind::Sequential, CharSet = CharSet::Unicode)]
ref class S {
public:
[MarshalAsAttribute(UnmanagedType::LPWStr)]
String ^ str;
[MarshalAsAttribute(UnmanagedType::ByValArray,
ArraySubType=UnmanagedType::I4, SizeConst=2)]
array<Int32> ^ intarr;
};
[DllImport("modify_ref_class_in_native_function.dll",
CharSet=CharSet::Unicode)]
int bar([In][Out] S ^ param);
int main() {
S ^ param = gcnew S;
param->str = "Hello";
param->intarr = gcnew array<Int32>(2);
param->intarr[0] = 100;
param->intarr[1] = 200;
bar(param); // Call to native function
Console::WriteLine("In managed: intarr: {0}, {1}",
param->intarr[0], param->intarr[1]);
}
str: Hello
In native: intarr: 100, 200
In managed: intarr: 300, 400