Question

In my C# application I have IntPtr y = VoidPointer(x); where VoidPointer(x) is an unmanaged function that returns a void*(void pointer). The problem is I am not getting the correct value pointed by y in the C# code. I am using Marshal.ReadInt32(y) and have tried ReadByte, ReadInt64 etc. Below are the code snippets,

Unmanaged function in C:

void* VoidPointer()
{
    int Var1 = 7113;
    return &Var1;
}

Managed function in C# :(using DllImport to access the unmanaged function.)

IntPtr z = VoidPointer();

Console.WriteLine(" z = {0} ", Marshal.ReadInt32(z));

But in the output I am not getting 7113. How can I access the correct value of Var1 in C# ?

Answer 1

VoidPointer returns a pointer to local variable which goes out of scope when the function ends. This is undefined behavior.

Try declaring Var1 as static:

void* VoidPointer()
{
    static int Var1 = 7113;
    return &Var1;
}