I'm getting a segmentation fault in GCC compiler-CodePudding

The segmentation error occurs in this function:

#include <stdio.h>
#include <stdlib.h>

int heap [999],heap2 [999]; 

int* addDigit(int *arr, int SIZE, int D) {
    int con=0;
    for (int i = 0; i < SIZE; i  )
        con = con * 10   arr[i];
    con  = D;

    int p = 0;
    while (con >= 0) {
        heap[p] = con % 10;
        con /= 10;
        p  ;
    }

    for (int i = 0; i < p; i  ) 
        printf("%d ", heap[i]);

    heap2[0] = 11;
    heap2[1] = -1;

    int *pp = heap2;

    return pp;
}

This is main function:

int main() {
    int N, digit; 
    scanf("%d", &N);
    int arr[N];
    for (int index = 0; index < N; index  ) {
        scanf("%d", &arr[index]);
    }

    scanf("%d", &digit);
    int *ptr = addDigit(arr, N, digit);
    int index = 0;
    while (*(ptr index) !=-1) {
        printf("%d", ptr[index]);
        index  ;
    }

    return 0;
}

Why am I getting a segmentation fault here?

This program gets input of array like [1 2 3] and value k, say 3; it should print 1 2 6.

I used two globally declared arrays here.

CodePudding user response：

Generally, the quickest way to locate the sources of segmentation faults, is the compile the program with the -g flag to include debug information in the executable, and then to run the program using Valgrind.

In this case, the segmentation fault occurs in the reading of heap here:

while (con >= 0)
{
    heap[p] = con % 10;
    con /= 10;
    p  ;
}

The variable con will eventually become 0 and will stay at 0 due to the repeated division by 10. It will not become negative, and thus the while-loop will repeat infinitely. The index p will increase until the program will try to access element 999 of heap - which is out of bounds, i.e. this is a segmentation fault.

Perhaps you meant to write while (con > 0)? This stop the loop when con is zero (instead of negative, as before). Or perhaps you need a different solution, depending on what the intended functionality of the code is exactly.

PS. The segmentation fault does not happen "in the compiler", it occurs while the program is executed.