Problem in writing structure to Binary file in C lang

Hi,
I had written application for storing employee data in binary file and
reading those data from binary file and display it in C language.
But I face some issue with writing data to binary file.
Here is my part of my code.

struct cust_data
{
	int nCAFID;
	char *szFirstName;
};

typedef struct cust_data CUST_DATA;
CUST_DATA *pCustdata = NULL;
int AddRecord()
{
           FILE *fp;
       	   fp = fopen("Input.dat","ab+");
	          return fp;
           pCustdata = malloc(sizeof(CUST_DATA));

           pCustData->szFirstName = malloc(sizeof(pCustData-
>szFirstName));

           printf("Enter CAFID : ");
           scanf("%d",&pCustData->nCAFID);

           printf("Enter First Name : ");
           scanf("%s",pCustData->szFirstName);

           fwrite(pCustData,sizeof(CUST_DATA),1,fp);

           fclose(fp);

           free(pCustData->szFirstName);
           free(pCustData)
}

now here when i write a structure to file, it writes nCAFID and
inplace of szFirstName it writes pointer to string.
But i need to write string..
if i take szFirstName as char array then it is wroking fine.....but i
want to use heap memory instead of stack..
can anyone help me..................??
thanks in advance.............