Fatal error LNK1169: one or more multiply defined symbols found

Question

I am getting this error:

fatal error LNK1169: one or more multiply defined symbols found

Below are two files containing the code. In file 1, I have the main() function and I am calling the functions which are written in the second file named linklist.cpp. Thanks for helping in advance.

File 1 - main.cpp

#include "stdafx.h"
# include "linklist.cpp"


int main(int argc, _TCHAR* argv[])
{
    node *link_list2;
    link_list2 = createList(31);
    addFront(link_list2,33);
    printList(link_list2);
    printf("Hello There Omer Obaid khan\n");
    return 0;
}

File 2 - linklist.cpp

# include "stdafx.h"
# include <stdlib.h>
struct node{
    node * next;
    int nodeValue;

};

node* initNode(int number);
node* createList (int value);
void addFront (node *head, int num );
void deleteFront(node*num);
void destroyList(node *list);
int getValue(node *list);

node*createList (int value)  /*Creates a Linked-List*/
{
    node *dummy_node = (node*) malloc(sizeof (node));
    dummy_node->next=NULL;
    dummy_node->nodeValue = value;
    return dummy_node;
}


void addFront (node *head, int num ) /*Adds node to the front of Linked-List*/
{
    node*newNode = initNode(num);   
    newNode->next = NULL;
    head->next=newNode;
    newNode->nodeValue=num;
}

void deleteFront(node*num)   /*Deletes the value of the node from the front*/
{
    node*temp1=num->next;

    if (temp1== NULL) 
    {
        printf("List is EMPTY!!!!");
    }
    else
    {
        num->next=temp1->next;
        free(temp1);
    }

}

void destroyList(node *list)    /*Frees the linked list*/
{
    node*temp;
    while (list->next!= NULL) 
    {
        temp=list;
        list=temp->next;
        free(temp);
    }
    free(list);
}

int getValue(node *list)    /*Returns the value of the list*/
{
    return((list->next)->nodeValue);
}


void printList(node *list)   /*Prints the Linked-List*/
{

    node*currentPosition;
    for (currentPosition=list->next; currentPosition->next!=NULL; currentPosition=currentPosition->next)  
    {
        printf("%d \n",currentPosition->nodeValue);
    }   
    printf("%d \n",currentPosition->nodeValue);

}

node*initNode(int number) /*Creates a node*/
{
    node*newNode=(node*) malloc(sizeof (node));
    newNode->nodeValue=number;
    newNode->next=NULL;
    return(newNode);
}

Solution 1

I stopped reading after # include "linklist.cpp". Don't include implementation files in other implementation files. (unless you're doing bulk-builds, which I doubt). Separate declarations in headers and include those, and keep the definitions in the implementation files.

Solution 2

You have two ways to solve your problem:

First is given in answer of Luchian Grigore. Create separate header and include it in main file.

Second one is exclude file linklist.cpp from build using project options. In other way this file will be build twice: during his own build and during main file build.

However, second way is not good programming style. It is better to create header file.

Comments

[OOkhan]

you want me to make .h file and put Signatures of funtion there and then include that header file in main ??

[SvenS]

yes, struct and function prototypes go into a header file, which is included both in main.cpp and linklist.cpp. The #include statement puts the whole content of one file into the file it is used in, so the functions are declared both in linklist.cpp and in main.cpp, that's why you get that error.

[OOkhan]

Mr.Luchian Grigore thanks for helping... Can you please tell why the error is coming ? Means what is logic behind? Now i make 1 header file and put prototype and struct there and include that header file on both .cpp files. why i can't just include .cpp file in other one?

[Luchian Grigore]

@OOkhan you're breaking the one definition rule (look it up). Basically, you can't define symbols multiple times. When you include the cpp file, it's contents are pasted in the current translation unit. So you'll define, for example, createList both in main.cpp AND linklist.cpp. Which is illegal. A header files should only contain declarations. What you have in the cpp file are definitions.

[OOkhan]

@LuchianGrigore what if i put prototypes in main and delete header file and did not include linklist.cpp Should it work?? if No then why not??

[OOkhan]

@LuchianGrigore But that's not a Good way right ??:) Thanks a Lot SIR

[Luchian Grigore]

@OOkhan it's not unusual, but having a header is preferred, yes.