Code to change the key in C

How to prepare data to change the key after encryption. Found the C++ example in GlobalKeyTransfer(). Not sure how to convert it to C.
The expected DLMS translator output:

<MethodInvocationParameters>
<Array Qty="01" >
<Structure Qty="02" >
<Enum Value="02" />
<OctetString Value="24 bytes key" />
</Structure>
</Array>
</MethodInvocationParameters>

Thank you.