releasing of pointer memory in unmanaged code

[nastoski]

Dear All,
i'm facing a problem with releasing of pointer mamory. Let me explain.

From a .NET environment I need to call custom API functions in a WIN32 dll written in C/C++. In order to do this I am writing a managed wrapper class using managed extensions for C++. I use the IJW approach by explicit marshalling. One of the API functions in the dll expects a char** pointer as argument and should return some data on that pointer. Here is sample code from my managed wrapper class:

…

IntPtr ptrToString = Marshal::StringToHGlobalAnsi(myStringBuilder ->ToString());

char *temp = (char*) ptrToString.ToPointer();

char **response = &temp;



int result = APIfunction(response);



IntPtr ptrToResponse = *response;

String *myData = Marshal:trToStringAnsi(ptrToResponse);



The data is transferred fine, however when I try to release the pointer memory I get:

if I try:

Marshal::FreeHGlobal(ptrToString); //ok



If I try:

Marshal::FreeHGlobal(ptrToResponse); //error:”The handle is invalid.”



If I try:

free(*response);

the freeing fails on _CrtIsValidHeapPointer(const void * pUserData);



The code in the API function from the dll uses

*response = (char*) malloc (size);

and then assigns some data to the pointer and after that the function returns.



It seems to me that the API in the dll allocates memory from it’s own Run-Time C local heap and assigns that address to *response

When I try to release the memory in my code it fails since the pointer points to a different local heap.



How to resolve the release of the pointer memory?

Please help,

Regards,
Igor

 

[cpjust]

The API must have a method that deletes the memory itself. See if it has a function that you can pass the pointer to and have it free it.
If you try to delete memory across a DLL boundary you'll blow up.