unresolved external errors - c++

Question

I have the following .h and .cpp files
If i have to I will include the full codes of the function definitions
When i compile my program i get the errors shown at the end
hash.h
#define BUCKETS 64
#define B_ENTRIES 50000
int curr_tanker;
typedef unsigned long int ulong;
typedef struct bucket
{
int bucket_id;
ulong bucket_entries;
}bucket;
typedef struct tanker_record
{
ulong tanker_id;
ulong tanker_size;
ulong num_of_entries;
ulong bucket_entry_count;
}tanker_record;
typedef struct fpinfo
{
unsigned long chunk_offset;
unsigned long chunk_length;
unsigned char fing_print[33];
}fpinfo;
struct fpinfo* InitHTable(fpinfo *);
int CreateTanker(tanker_record tr[]);
int Hash_CreateEntry(struct fpinfo *,struct fpinfo he,tanker_record tr);
ht.cpp
#include <stdlib.h>
#include <string.h>
#include<stdio.h>
#include <iostream>
#include "ht.h"
struct fpinfo* InitHTable(struct fpinfo ht[][B_ENTRIES])
{
}
int CreateTanker(tanker_record tr[])
{
}
int
Hash_CreateEntry(struct fpinfo *t[][B_ENTRIES],struct fpinfo he,tanker_record tr[])
{
}
static void
WriteHTtoFile(struct fpinfo *t[][B_ENTRIES],int this_tanker)
{
}
main.cpp
#include<iostream>
#include"ht.cpp"
#include<conio.h>
#include<stdlib.h>
void main(int argc, char **argv)
{
static fpinfo hash_table[BUCKETS][B_ENTRIES];
static tanker_record tr[100];
InitHTable(&hash_table[0][0]);
CreateTanker(tr);
struct fpinfo fp;
...
ar = Hash_CreateEntry(&hash_table[0][0], fp,tr[0]);
i get the following errors when i try to compile it using vc2010
1>main.obj : error LNK2005: "struct fpinfo * __cdecl InitHTable(struct fpinfo (* const)[50000])" (?InitHTable##YAPAUfpinfo##QAY0MDFA#U1##Z) already defined in ht.obj
1>main.obj : error LNK2005: "int __cdecl CreateTanker(struct tanker_record * const)"
(?CreateTanker##YAHQAUtanker_record###Z) already defined in ht.obj
1>main.obj : error LNK2005: "int __cdecl Hash_CreateEntry(struct fpinfo * (* const)[50000],struct fpinfo,struct tanker_record * const)" (?Hash_CreateEntry##YAHQAY0MDFA#PAUfpinfo##U1#QAUtanker_record###Z) already defined in ht.obj
1>main.obj : error LNK2005: "int curr_tanker" (?curr_tanker##3HA) already defined in ht.obj
1>main.obj : error LNK2019: unresolved external symbol "int __cdecl Hash_CreateEntry(struct fpinfo *,struct fpinfo,struct tanker_record)"
(?Hash_CreateEntry##YAHPAUfpinfo##U1#Utanker_record###Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "struct fpinfo * __cdecl InitHTable(struct fpinfo *)" (?InitHTable##YAPAUfpinfo##PAU1##Z) referenced in function _main
THANKS FOR YOUR HELP!!

Answer 1

You're including ht.cpp from main.cpp, which will include all the definitions of functions already defined in ht.cpp itself.
You want to include ht.h instead.
It won't help in this situation, but you should also protect the header file with include guards:
#ifndef HT_H
#define HT_H
// contents of ht.h
#endif
You also need the arguments of the function declarations to match those of the definitions:
struct fpinfo* InitHTable(struct fpinfo[][B_ENTRIES]);
// Missing: ^^^^^^^^^^^
int CreateTanker(tanker_record tr[]); // OK
int Hash_CreateEntry(struct fpinfo*[][B_ENTRIES],struct fpinfo,tanker_record[]);
// Missing ^^^^^^^^^^^^^ ^^

Answer 2

Add an "include guard" in your header, so that it its contents aren't "seen" twice after preprocessing. For Microsoft, #pragma once at the beginning of the .h file. In general, add:
#ifndef __YOUR_HEADER_H
#define __YOUR_HEADER_H
// all the stuff from the header here
#endif
Make sure to adopt a consistent "unique" naming scheme for each of your headers. __YOUR_HEADER_H would do, for example customio.h into __CUSTOM_IO_H.