How to Convert String^ Array to Void* Array

I'm assuming that void* ptrArr[100] is actually const char* ptrArr[100]. void* could be literally anything, so there's no way to answer the question without making an assumption about the type.

So, you need two things here: You need to do the conversion between types (including from Unicode code points to ANSI characters), and you need to have something own that memory.

There's a few choices as to what should hold the unmanaged memory for the const char*. The most do-it-yourself route is Marshal.StringToHGlobalAnsi, but that's a pain so we're going to skip that. (This would require manually keeping track of a bunch of IntPtr, and manually calling FreeHGlobal when done.)

The other choices are different invocations of marshal_as.

You could convert all the String^ instances into std::string instances, and pull the const char* out of them. I recommend marshal_as<std::string> for this. In this case, the memory is owned by the std:string instances, so ptrArr will be valid only for as long as stdStrArr is.

#include <msclr\marshal_cppstd.h>

array<String^>^ strArr = gcnew array<String^>(100);
std::string stdStrArr[100];
const char* ptrArr[100];

for (size_t i = 0; i < 100; i++)
{
    stdStrArr[i] = marshal_as<std::string>(strArr[i]);
    ptrArr[i] = stdStrArr[i].c_str();
}
// Memory for ptrArr deallocated when stdStrArr goes out of scope. 

The other choice is to use marshal_as to convert directly to const char*. To do this, you allocate a helper object. In this case, the memory is owned by the marshal_context instance, so ptrArr will be valid only for as long as context is.

#include <msclr\marshal.h>

array<String^>^ strArr = gcnew array<String^>(100);
marshal_context^ context = gcnew marshal_context();
char* ptrArr[100];

for (size_t i = 0; i < 100; i++)
{
    ptrArr[i] = context->marshal_as<const char*>(strArr[i]);
}
// Memory for ptrArr deallocated when you call `delete context`, or when it's garbage collected. 

Further reading:

• Overview of Marshaling in C++
• marshal_context::marshal_as (Shows an example of using a marshal_context.)

_Notes:

• _{I didn't check my syntax with a compiler. There may be small errors.}
• _{It seems like there should be a question to mark this one a duplicate. However, I wasn't able to find a "convert String^ to char*" question that was highly-rated, used marshal_as in the answer, and showed a good example of how to use it.}