error LNK2001: unresolved external symbol "int * array"

Question

when i try to compile it i have this error , and i really have no idea what to do . Maybe you can help me about this .

Main.cpp:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <list>
using namespace std;

list<int> liste;
int size=0;

void list_initialization(){
    cout << "Quicksort" << endl << endl;
    cout <<"List Initialization" << endl;
    while ((size<1)||size>100){
        cout << "Please enter the size (between 1 and 100)" << endl;
        cin >> size;
    }
    srand ( time(NULL) );
    for (int i=0; i<size; i++){
        liste.push_back(rand() %100 +1);
    }
}

void list_display(){
    cout << endl;
    for (list<int>::const_iterator ite=liste.begin(), end=liste.end(); ite!=end; ++ite)
            cout << *ite << " ";
    cout << endl;
}

int choose_pivot( int const& left, int const& right){
    int pivot;
    pivot = rand()%(right-left) + left ;
    return pivot;
}

int partition(int left, int right, int pivotIndex){


    //We Save pivotValue
    list<int>::iterator itPivotIndex = liste.begin();
    advance (itPivotIndex, pivotIndex);
    int pivotValue = *itPivotIndex;

    //Those 2 iterators will be used to swap 2 elements
    list<int>::iterator itSwap1 = liste.begin();
    list<int>::iterator itSwap2 = liste.begin();

    //2 iterators to point left and right elements
    list<int>::iterator itLeft = liste.begin();
    advance (itLeft, left);
    list<int>::iterator itRight = liste.begin();
    advance (itRight, right);

    //1 iterator to point the StoreIndex
    list<int>::iterator itStoreIndex=itLeft;


    //Move Pivot to End
    advance(itSwap1, pivotIndex);
    advance(itSwap2, right);
    swap(*itSwap1, *itSwap2);


    //Move all elements less than pivotValue before the pivot

    for(list<int>::iterator it=itLeft; it!=itRight; it++)
        if (*it < pivotValue){

            //Swap array[k] and array[storeIndex]
            itSwap1=it;
            itSwap2=itStoreIndex;
            swap(*itSwap1, *itSwap2);

            itStoreIndex++;
        }

    //Move pivot to its final place
    swap(*itStoreIndex, *itRight);

    return (distance(liste.begin(), itStoreIndex));
}


void quicksort (int left, int right){

    int pivotNewIndex=0;
    list<int>::iterator ite=liste.begin();

    if (left < right){

        int pivotIndex = choose_pivot(left,right);
        advance (ite,pivotIndex);
        cout << "The pivot is " << *ite <<endl;

        pivotNewIndex = partition(left, right, pivotIndex);

        list_display();
        cout << endl;

        // Recursively sort elements smaller than the pivot
    quicksort(left, pivotNewIndex - 1);

        // Recursively sort elements at least as big as the pivot
    quicksort(pivotNewIndex + 1, right);
    }

}

int main()
{
    list_initialization();
    list_display();
    cout << endl;

    int left=0;
    int right=size-1;

    quicksort(left, right);
    cout << "Sorted List :";
    list_display();

    cout << endl;
    return 0;

}

quicksort.cpp:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <list>
using namespace std;

 extern int array [];

int selectPivot( int const& left, int const& right);
int Partition(int left, int right, int pivotIndex);
void sorting (int left, int right);

int selectPivot( int const& left, int const& right){
    int pivot;
    pivot = rand()%(right-left) + left ;
    return pivot;
}

int Partition(int left, int right, int pivotIndex){

    int temp=0;
    int storeIndex=left;
    int pivotValue = array[pivotIndex];


    temp=pivotValue;
    pivotValue=array[right];
    array[right]=temp;


    for (int k=left; k<right; k++)
        if (array[k] < pivotValue){

            temp=array[k];
            array[k]=array[storeIndex];
            array[storeIndex]=temp;

            storeIndex++;
        }

    temp = array[storeIndex];
    array[storeIndex]=array[right];
    array[right]=temp;

    return storeIndex;
}


void sorting (int left, int right){

    int pivotNewIndex=0;

    if (left < right){

        int pivotIndex = selectPivot(left,right);

        pivotNewIndex = Partition(left, right, pivotIndex);


        sorting(left, pivotNewIndex - 1);


        sorting(pivotNewIndex + 1, right);
    }

}

-------------- 1>------ Build started: Project: practical2, Configuration: Debug Win32 ------ 1>Compiling... 1>quicksort.cpp 1>Linking... 1>quicksort.obj : error LNK2001: unresolved external symbol "int * array" (?array@@3PAHA) 1>C:\Users\Amed\Documents\Visual Studio 2008\Projects\practical2\Debug\practical2.exe : fatal error LNK1120: 1 unresolved externals 1>Build log was saved at "file://c:\Users\Amed\Documents\Visual Studio 2008\Projects\practical2\practical2\Debug\BuildLog.htm" 1>practical2 - 2 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

You could fix the unresolved external by changing it to: int array[1024];

Notes: 1024 was chosen arbitrarily as the array dimension. Choosing the dimension(s) of a statically defined C-style array is tricky at times. You can avoid this issue by switching to a dynamic structure like the Standard Library's std::vector class: std::vector nameOtherThanArray; // ;)

Naming the (global) variable "array" is probably too genetic to impart expected use in addition to possibly clashing with names in other libs. I did not attempt to code review the rest but if I were writing a real general purpose method, I'd want to pass in the structure being manipulated, or if it's just a temporary helper, declare it locally. Of course, like I said I didn't closely examine the rest of the code so your way may make sense for other reason.

Answer 2

You wrote extern int array[] in quicksort.cpp, but didn't actually define it anywhere. There's an unresolved symbol because it doesn't exist anywhere, so the linker can't find it to resolve it.