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A strange limit for my quicksorting code

oldspiderdude (17)
Here is my code

The problem is when I change nNum, the size of the array,
to 520241, the thing crashes. When it is 520240, the program
(without printing all the values) runs within a second. I
changed every number in this code to long, same problem.

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#include <iostream>
#include <stdlib.h>

using namespace std;

long maxN, nNum;
bool spaceBefore;


void qSort(long unsorted[], long begCursor, long endCursor) {
    if (begCursor>=endCursor) {
        return;
    }
    long pivot=endCursor;
    long wall=begCursor, cTL=begCursor; //cTL means "check if could switch to left"
    bool nothingDone;
    while (wall<=pivot-(long)1&&cTL<=endCursor) {
        nothingDone=true;
        if (unsorted[wall]<unsorted[pivot]) {
            wall++;
            nothingDone=false;
            if (cTL<=wall) {
                cTL=wall+(long)1;
            }
            if (wall==pivot-(long)1) {
                continue;
            }
            continue;
        }
        else if (cTL<endCursor&&unsorted[wall]>=unsorted[pivot]) {
            while (cTL<endCursor) {
                if (unsorted[cTL]<unsorted[pivot]) {
                    unsorted[cTL]=unsorted[cTL]^unsorted[wall];
                    unsorted[wall]=unsorted[cTL]^unsorted[wall];
                    unsorted[cTL]=unsorted[cTL]^unsorted[wall];
                    cTL++;
                    wall++;
                    nothingDone=false;
                    break;
                }

                cTL++;
                nothingDone=false;
            }
        }
        if (nothingDone) {break;}
        if (cTL>=endCursor) {
                break;}


    }
    if ((pivot!=wall)&&(unsorted[pivot]!=unsorted[wall])) {
    unsorted[pivot]=unsorted[pivot]^unsorted[wall];
    unsorted[wall]=unsorted[pivot]^unsorted[wall];
    unsorted[pivot]=unsorted[pivot]^unsorted[wall];}
    long nextEnd=wall-(long)1;
    long nextStart=wall+(long)1;
    qSort(unsorted,begCursor,nextEnd);
    qSort(unsorted,nextStart,endCursor);
    return;
}


int main()
{
    maxN=10000000;
    nNum=520241; //currently it crashes
    // cin >> maxN >> nNum;
    long unsorted[nNum];
    for (long loop=0; loop<nNum;loop++) {
        unsorted[loop]=rand()%(maxN+1);
    }
    qSort(unsorted,(long)0,nNum-(long)1);
    /* spaceBefore=false;
    for (long loop=0; loop<nNum;loop++) {
        if (spaceBefore==true) {
            cout << " ";
        }
        cout << unsorted[loop];
        spaceBefore=true;
    } */
    return 0;
}

Last edited on
JLBorges (13770)
You may be running out of stack space. Try using an array with a static storage duration.
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// long unsorted[nNum]; // line 69
static long unsorted[nNum];
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