Why am I getting this linker error?

I don't understand why I'm getting this error:

g++ -o tht testhashtable.o
/usr/lib/gcc-lib/i386-redhat-linux/2.96/../../../crt1.o: In function `_start':
/usr/lib/gcc-lib/i386-redhat-linux/2.96/../../../crt1.o(.text+0x18): undefined reference to `main'
collect2: ld returned 1 exit status

Compilation exited abnormally with code 1 at Mon Dec 3 14:15:07

when I try to link the object file created by this code:

#include <iostream>
#include <fstream>
//using namespace std;
#include <stdlib.h>
#include "HashTable.h"
#include "HashableString.h"

#ifdef TEST_HASHTABLE

void main(void)//int argc, char *argv[])
{
HashTable<HashableString> ht(3);

string str;
char in[256];

while(true)
{

cout << "Enter Command : ";
gets(in);
str = in;

if(str == "q" || str == "")
{
cout << "Execution complete" << endl;
break;
}

if(str[0] == 'i')
{
string tmp = str.substr(2, str.length()-2);
HashableString htmp = tmp;

ht.search_and_insert(htmp);
}

if(str[0] == 's')
{
string tmp = str.substr(2, str.length()-2);
HashableString htmp = tmp;

if(ht.search(htmp))
{
cout << "Found in table " << endl;
}
else
{
cout << "Not found " << endl;
}
}

ht.debug_print();

}

return EXIT_SUCCESS;
}

#endif

Any help is much appreciated. TIA.