CODEWITHSUNDEEP
cvisual-studio-code
user4572034
user4572034

Reputation:

Why does my c code crash when run from VSCode terminal, but runs fine when run from gnome terminal?

Memory seems to run out when I run the executable from within the Visual Studio Code terminal, and then my computer freezes.

But all is fine when I run it from gnome terminal, and I get the desired outputs.

I'm not yet knowledgeable about c or the gmp.h library. I wouldn't be surprised if there is a bug somewhere, or something I am missing, even if the code I've posted does give me correct results when not run from VSCode.

Btw it does take about 1m43s to run, with N 666666, on my pc.

// problem from: https://www.reddit.com/r/dailyprogrammer/comments/jfcuz5/20201021_challenge_386_intermediate_partition/
#include "gmp.h"
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#define N 666666

mpz_t results[N + 1];

void segment(int n)
{
    if (n <= 1)
        return;
    if (mpz_cmp_ui(results[n - 1], 0) > 0)
        return;

    mpz_t result;
    mpz_t diff;
    mpz_init(result);
    mpz_init(diff);
    int i = 0;
    int seq = 1;
    int is_positive;

    while (n - seq >= 0)
    {
        segment(n - seq);
        is_positive = 1 - 2 * (i / 2 % 2);
        mpz_mul_si(diff, results[n - seq - 1], is_positive);
        mpz_add(result, result, diff);
        seq += (i % 2 > 0) ? i + 2 : (i + 2) / 2;
        i += 1;
        mpz_set_ui(diff, 0);
    }

    mpz_add_ui(results[n - 1], result, 0);
    mpz_clear(result);
    mpz_clear(diff);
    return;
}

int main(void)
{
    for (int i; i < N; i++)
    {
        mpz_init(results[i]);
    }
    mpz_set_ui(results[0], 1);
    mpz_set_ui(results[1], 1);

    for (int i; i <= N + 1; i++)
    {
        segment(i);
    }

    gmp_printf("Result: %Zd\n", results[N]);

    for (int i; i < N; i++)
    {
        mpz_clear(results[i]);
    }
}

Upvotes: 0

Views: 567

Answers (1)

chqrlie
chqrlie

Reputation: 144989

The code has undefined behavior because the for loops do not initialize the i loop index: for (int i; i < N; i++) Furthemore, the array has N + 1 elements, so the initialization loop should run one step farther and the segment loop one less.

Modify the main() function to:

int main() {
    for (int i = 0; i < N + 1; i++) {
        mpz_init(results[i]);
    }
    mpz_set_ui(results[0], 1);
    mpz_set_ui(results[1], 1);

    for (int i = 0; i < N + 1; i++) {
        segment(i);
    }

    gmp_printf("Result: %Zd\n", results[N]);

    for (int i = 0; i < N + 1; i++) {
        mpz_clear(results[i]);
    }
    return 0;
}

Upvotes: 1

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