Make C file for create type

Hallo,
I found a problem making new data type kata,expecially
when make the C file ,can anyone help me solve it.

This error occur when I'm compiling the C file :
/usr/lib/gcc-lib/i586-suse-linux/3.3.1/../../../crt1.o(.text+0x18):
In function `_start':
../sysdeps/i386/elf/start.S:98: undefined reference to
`main'
collect2: ld returned 1 exit status

Here it's my code :
file3.c
-------
#include "postgres.h"

typedef struct kata
{
char kt[30];
} kata;

kata *input_kata(char *str);
char *output_kata(kata * kata);

kata *
input_kata(char *str)
{
char kt[30];
kata *result;

if (sscanf(str, "( %s )", &kt) !=1)
{
printf ("error\n");
return NULL;
}

result = (kata *) malloc(sizeof(kata));
strcpy(result->kt,kt);
return result;
}

char *
output_kata(kata * kata)
{
char kt[30];
char *result;

strcpy(kt,kata->kt);

if (strcmp(kt,NULL))
return NULL;

result = (char *) malloc(60);
sprintf(result, "(%s)", kata->kt);
return result;
}

kata.sql
--------
CREATE FUNCTION input_kata(cstring)
RETURNS kata
AS '_OBJWD_/file3'
LANGUAGE C IMMUTABLE STRICT;

CREATE FUNCTION output_kata(kata)
RETURNS cstring
AS '_OBJWD_/file3'
LANGUAGE C IMMUTABLE STRICT;

CREATE TYPE kata (
INPUT = input_kata,
OUTPUT = output_kata
)

____________________________________________________
Start your day with Yahoo! - make it your home page
http://www.yahoo.com/r/hs