为什么我的程序在运行后给出"segmentation fault"(核心转储)错误

我必须使用信号量创建一个素数检查器。代码执行直到"从中查找素数"部分，然后崩溃并显示"分段错误（核心转储）"。搜索后，我了解到当程序尝试访问不可用的内存部分时会发生这种情况;但我在我的代码中不明白它。请看一看，谢谢！

#include <QThread>
#include <QSemaphore>
#include <QMutex>
#include <iostream>
#include <stdlib.h>
#include <cmath>
#include <vector>
using namespace std;
#define TOTALSPACE 50
vector<int> buffer(TOTALSPACE);
QSemaphore space(TOTALSPACE), avail;
QMutex l;
int prime_from, prime_to, num_threads;
int total = 0, cnumber = 0;
int in = 0, out = 0;
bool b = false;
//-----Generator------
class Generator : public QThread
{
private:
    int strt;
    int end;
public:
    Generator(int a, int b)
    {
        strt = a;
        end = b;
        cnumber = strt;
    }
    void run()
    {
        while (cnumber < end)
        {
            space.acquire();
            cnumber++;
            buffer[in] = cnumber;
            in = (in + 1) % TOTALSPACE;
            avail.release();
        }
        b = true;
        for (int i = 0; i < num_threads; i++)
        {
            space.acquire();
            buffer[in] = -1;
            in = (in + 1) % TOTALSPACE;
            avail.release();
        }
    }
};
//-----------Checker----------
class Checker : public QThread
{
private:
    int number;
public:
    Checker() {}
    void run();
};
void Checker::run()
{
    while (1)
    {
        avail.acquire();
        l.lock();
        number = buffer[out];
        if (number == -1)
        {
            l.unlock();
            break;
        }
        bool isPrime = false;
        for (int i = 2; i <= sqrt(number); i++)
        {
            if (number%i == 0)
            {
                isPrime = true;
                break;
            }
        }
        out = (out + 1) % TOTALSPACE;
        if (isPrime == false)
        {
            total++;
        }
        l.unlock();
        space.release();
    }
}
//-------------Main---------
int main(int argc, char *argv[])
{
    num_threads = atoi(argv[1]);
    prime_from = atoi(argv[2]);
    prime_to = atoi(argv[3]);
    cout << " Number of Threads = " << num_threads << endl;
    cout << " Primes checking from " << prime_from << " to " << prime_to << endl;
    Generator gen(prime_from, prime_to);
    gen.start();
    Checker* thr[num_threads];
    for (int i = 1; i < num_threads; i++)
    {
        thr[i] = new Checker();
        thr[i]->start();
    }
    gen.wait();
    for (int i = 0; i < num_threads; i++)
    {
        thr[i]->wait();
    }
    cout << "Total Primes: " << total << endl;
    return 0;
}