GNU GCC compilor error "multiple definition of main"

Question

I am new to ubuntu, now I need to develop my assignment in C++. I am using codeblocks IDE to write c++ programs. Whenever I compile something in it, it gives these errors:

multiple definition of main
warning: control reaches end of non-void function

Here is the code I want to compile for now:

#include <iostream>
#include <stdlib.h>
using namespace std;
/* The Node class */
class Node
{
    public:
        int get() { return object; };
        void set(int object) { this->object = object; };
        Node * getNext() { return nextNode; };
        void setNext(Node * nextNode) { this->nextNode = nextNode; };
    private:
        int object;
        Node * nextNode;
};
/* The List class */
class List
{
    public:
        List();
        void add (int addObject);
        int get();
        bool next();
        friend void traverse(List list);
        friend List addNodes();

    private:
        int size;
        Node * headNode;
        Node * currentNode;
        Node * lastCurrentNode;
};
/* Constructor */
List::List()
{
    headNode = new Node();
    headNode->setNext(NULL);
    currentNode = NULL;
    lastCurrentNode = NULL;
    size = 0;
}

/* add() class method */
void List::add (int addObject)
{
    Node * newNode = new Node();
    newNode->set(addObject);
    if( currentNode != NULL )
    {
        newNode->setNext(currentNode->getNext());
        currentNode->setNext( newNode );
        lastCurrentNode = currentNode;
        currentNode = newNode;
    }
    else
    {
        newNode->setNext(NULL);
        headNode->setNext(newNode);
        lastCurrentNode = headNode;
        currentNode = newNode;
    }
    size ++;
}
/* get() class method */
int List::get()
{
    if (currentNode != NULL)
        return currentNode->get();
}
/* next() class method */
bool List::next()
{
    if (currentNode == NULL) return false;
    lastCurrentNode = currentNode;
    currentNode = currentNode->getNext();
    if (currentNode == NULL || size == 0)
        return false;
    else
        return true;
}
/* Friend function to traverse linked list */
void traverse(List list)
{
    Node* savedCurrentNode = list.currentNode;
    list.currentNode = list.headNode;

    for(int i = 1; list.next(); i++)
    {
        cout << "\n Element " << i << " " << list.get();
    }
    list.currentNode = savedCurrentNode;
}
/* Friend function to add Nodes into the list */
List addNodes()
{
    List list;
    list.add(2);
    list.add(6);
    list.add(8);
    list.add(7);
    list.add(1);
    cout << "\n List size = " << list.size <<'\n';
    return list;
}
int main()
{
    List list = addNodes();
    traverse(list);
    return 0;
}

Can anyone explain, where do I messing up?

`List::get()` has a control path that exits the function without returning a value (i.e. when the condition in the `if` is false). — Niall, Oct 29 '14 at 08:58
Post your code not a link, also you function `int List::get()` won't return anything unless the boolean condition is satisfied, hence the error — EdChum, Oct 29 '14 at 08:59
Show your compilation command. Try first to compile on the command line in a terminal, using `g++ -Wall -Wextra -g`. — Basile Starynkevitch, Oct 29 '14 at 08:59
Next time post I) code, not a rotting link, II) a minimal testcase — Sebastian Mach, Oct 29 '14 at 08:59
Please add parameters to you `main` function: `int main ( int argc, char* argv[] )` — sfrehse, Oct 29 '14 at 09:00
... and III) What have you tried already? Are you really dead sure that for the error message posted, you don't find any results on stack overflow or your facourite web search already? — Sebastian Mach, Oct 29 '14 at 09:01
just commented out the `main` now its not giving any error, but now it not working according to my requirements? — arximughal, Oct 29 '14 at 09:05
Your codeblocks IDE is probably mis-configured, so avoid it. You should instead use a good editor like `emacs` and compile on the command line in a terminal. Later, learn about `make` — Basile Starynkevitch, Oct 29 '14 at 09:08
It compiles successfully on my system... I don't know what is wrong.... — mlwn, Oct 29 '14 at 09:08
hmm... I'd learn about `emacs` and `make` , but now I've to finish this by the eve, any way how can I overcome this for now, any tutorial to configure codeblocks properly? — arximughal, Oct 29 '14 at 09:09
I compiled it with ultimate++, using `theIde` .. and it works — mlwn, Oct 29 '14 at 09:10
as @sfrehse suggested, please check your IDE... the problem is there !!!!!! you can always show your compile flags/settings... — mlwn, Oct 29 '14 at 09:22

score 3 · Answer 1 · answered Oct 29 '14 at 08:59

3

It seems that your IDE is not just compiling one single file, but another one which also contains a definition of the main function. Please check out how many files are being compiled.

In addition, your compiled is treating all the warnings as errors (-Werror) or disable this flag.

answered Oct 29 '14 at 08:59

Didac Perez Parera

3,734
3
52
87

You may return -1 if current == NULL in int List::get() – Didac Perez Parera Oct 29 '14 at 09:17
tried it, now its just giving single error `multiple definition of main` :( – arximughal Oct 29 '14 at 09:21
1

Do not disable the flag. _Fix the warning_. – Lightness Races in Orbit Oct 29 '14 at 12:54
The Problem was as same as you said in your answer @DídacPérez, the IDE was compiling multiple files at once, now I tried with single file and it worked correctly. – arximughal Oct 29 '14 at 15:39
I am happy to know that you have solved your problem. Could you please mark my answer as the right answer? – Didac Perez Parera Oct 30 '14 at 08:19

score 3 · Answer 2 · edited May 23 '17 at 11:53

3

The program compiles fine with (yourcode.cc contains your sourcecode):

$ CXXFLAGS="-Wall -Werror -Wpedantic" make yourcode

stack.cc: In member function ‘int List::get()’:
stack.cc:76:1: error: control reaches end of non-void function [-Wreturn-type]
 }

and invoking ./yourcode outputs:

 List size = 5

 Element 1 2
 Element 2 6
 Element 3 8
 Element 4 7
 Element 5 1

Obviously your IDE is going to add some flags to the linker. Please show us your compile flags/setting. See the compile log or run the make command executing more verbose.

May have a look at. Code::blocks verbose build

edited May 23 '17 at 11:53

Community

1
1

answered Oct 29 '14 at 09:13

sfrehse

1,062
9
22

2

-1: All you're doing here is training the OP to _ignore_ important compiler warnings. Why? I also don't see how this is an answer, let alone a +3 answer, since you didn't address the OP's problem at all. – Lightness Races in Orbit Oct 29 '14 at 12:54
1

Sure, but it shows that the code itself is okay and implies anything is wrong with the build environment. – sfrehse Oct 29 '14 at 13:37
But the code is _not_ okay. There was a warning indicating that. You chose to ignore it and taught the OP to ignore it. Why? – Lightness Races in Orbit Oct 29 '14 at 14:36
Yes, the problem with the return value was already discussed above. You are completely right, compilation with sufficient flags is definitely required to show those simple static problems. – sfrehse Oct 29 '14 at 14:42

score 0 · Accepted Answer · edited Oct 29 '14 at 18:26

The Problem was just, my IDE was compiling multiple files at once, and also in the function int List::get() , I got to add else return -1 at the end of this function after if statement,
I mean before editing my code the int List::get() function was like this:

int List::get() {
    if (currentNode != NULL)
        return currentNode->get();
}

I replaces this one with:

int List::get() {
    if (currentNode != NULL)
        return currentNode->get();
    else return -1;
}

and it worked fine.

GNU GCC compilor error "multiple definition of main"

3 Answers3

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