I have the following C++ structs
struct InnerStruct
{
int A;
int B;
};
struct OuterStruct
{
int numberStructs;
InnerStruct* innerStructs;
};
And a C++ function
OuterStruct getStructs();
How can I marshal this to C#? Where the C# definitions is
struct OuterStruct {
InnerStruct[] innerStructs;
};
You'll have to do this manually, since there's no way to tell the P/Invoke layer how much data to marshal from your C++ return value.
struct OuterStruct {
int numberStructs;
IntPtr innerStructs;
};
OuterStruct s = getStructs(); // using DllImport
var structSize = Marshal.SizeOf(typeof(InnerStruct));
var innerStructs = new List<InnerStruct>();
var ptr = s.innerStructs;
for (int i = 0; i < s.numberStructs; i++)
{
innerStructs.Add((InnerStruct)Marshal.PtrToStructure(ptr,
typeof(InnerStruct));
ptr = ptr + structSize;
}
Note that if you want to free the memory for innerStructs from your C# code, you have to use the standard allocator CoTaskMemAlloc in your C++ code--then you can call Marshal.CoTaskMemFree to free innerStructs.
int? What if it is running in a 64-bit process?! You don't need the casts
IntPtr to int in a case such that. Please don't!