怎么把由从C++写的系统改写成C

如何把由从C++写的系统改写成C？
如何把由从C++写的系统改写成C？有经验的朋友请指点一下。谢谢～！

[解决办法]
struct A{
struct A_struct *dat;
struct {
type (*fun2)();
void* (*Create)();
void (Destroy)();
void* (*op)(void*,void*);
...} pub;
struct {
type (*fun1)();
...} prv;
...};
AInit(struct A* a)
{
a-> pub.Create = A_Create;
a-> pub.Destroy = A_Destroy;
a-> pub.fun2 = A_fun2;
a-> pub.op = A_op;
a-> prv.fun1 = A_p_fun1;
a-> dat = A_Create();
...
};