Hello I was asked to serialize these two linked list classes.

typedef struct _List
{
	int len;
	char *p;
	float f;
	int count;
	ENTRY **pEntry;
	struct _List *pNext;
}LIST;

typedef struct _Entry 
{
	int len;
	char *p;
	double d;
} ENTRY;

I told him about using a string like we serailize a binary tree (1,2,3) but he was not satisfied. The interviewer was keen on saving memory and did not want me to use a string. I suggested stream but still he expected something better. Can anybody help with this question?