循环队列Segmentation fault的产生原因

Question

请问为什么循环队列这段代码会爆出Segmentation fault的错误啊？

#include <iostream>
#include <cmath>

using namespace std;

struct elem
{
    int *arr;
    int maxSize;
    int front,rear;
};
void create(elem *p,int a)
{
    p->arr=new int [a];
    p->maxSize=a;
    p->front=p->rear=0;
}
void clear(elem *p)
{
    delete [] p->arr;
}

bool isEmpty(elem *p)
{
    return p->front==p->rear;
}
void doubleSpace(elem *p)
{
    int *tmp=p->arr;
    p->arr=new int [2*(p->maxSize)];
    for (int i=1;i<p->maxSize;++i) p->arr[i]=tmp[(p->front+i)%p->maxSize];
    p->front=0;p->rear=p->maxSize-1;
    (p->maxSize)*=2;
    delete tmp;
}
void deQueue(elem *p)
{
    if(!isEmpty(p))
    {p->front = (p->front+1)%p->maxSize;
    cout << p->front <<' '<<abs((p->rear)-(p->front))<<endl;
    }
    else {
        cout << p->front <<' '<<abs((p->rear)-(p->front))<<endl;
    }
}
void enQueue(elem *p,int i)
{   if((p->rear+1)%p->maxSize==p->front) doubleSpace(p);
    p->rear=(p->rear+1)%p->maxSize;
    p->arr[p->rear]=i;
  cout << p->rear <<' '<<abs((p->rear)-(p->front))<<endl;
}
int getHead (elem *p)
{
    return p->arr[(p->front+1)%p->maxSize];
}

int main()
{   elem *p;



    int m,n,b;
    cin >> m >> n;
    create (p,m);
    b=n;
    while (b-->0)
    {
        int i;
        cin>>i;
        switch(i){
        case 0: int x;
        cin>>x;
        enQueue(p,x);break;
        case 1:deQueue(p);break;
        }
    }
    clear (p);
    return 0;

}

Answer 1

基于Monster 组和GPT的调写：

#include <iostream>
#include <cmath>
 
using namespace std;
 
struct elem
{
    int *arr;
    int maxSize;
    int front,rear;
};
void create(elem *p,int a)
{
    p->arr=new int [a];
    p->maxSize=a;
    p->front=p->rear=0;
}
void clear(elem *p)
{
    delete [] p->arr;
}
 
bool isEmpty(elem *p)
{
    return p->front==p->rear;
}
void doubleSpace(elem *p)
{
    int *tmp=p->arr;
    p->arr=new int [2*(p->maxSize)];
    for (int i=1;i<p->maxSize;++i) p->arr[i]=tmp[(p->front+i)%p->maxSize];
    p->front=0;p->rear=p->maxSize-1;
    (p->maxSize)*=2;
    delete[] tmp;
}
void deQueue(elem *p)
{
    if(!isEmpty(p))
    {
        p->front = (p->front+1)%p->maxSize;
        cout << p->front <<' '<<abs((p->rear)-(p->front))<<endl;
    }
    else {
        cout << p->front <<' '<<abs((p->rear)-(p->front))<<endl;
    }
}
void enQueue(elem *p,int i)
{   
    if((p->rear+1)%p->maxSize==p->front) doubleSpace(p);
    p->rear=(p->rear+1)%p->maxSize;
    p->arr[p->rear]=i;
    cout << p->rear <<' '<<abs((p->rear)-(p->front))<<endl;
}
int getHead (elem *p)
{
    return p->arr[(p->front+1)%p->maxSize];
}
 
int main()
{   
    elem q;
    elem *p=&q;
 
    int m,n,b;
    cin >> m >> n;
    create(p, m);
    b=n;
    while (b-->0)
    {
        int i;
        cin>>i;
        switch(i){
        case 0: 
            int x;
            cin>>x;
            enQueue(p,x);
            break;
        case 1:
            deQueue(p);
            break;
        }
    }
    clear(p);
    return 0;
 
}