问为什么当我试图从双链接列表中删除最后一个元素时，我会收到一个“信号SIGSEGV，分段错误”？

EN

get (dl=..., val=<error reading variable>) at dlist.h:37

#include <iostream>
#include <exception>


    
struct DListElem {          //element of the list
    int info;
    DListElem * prev;
    DListElem * next;
};
    
struct DList{               //just stores pointers to first and last elements of the list
    DListElem * first;
    DListElem * last;
};


void initializeDList(DList & dl){  //Iinitializes dl as empty list

    dl.first = nullptr;
    dl.last = nullptr;
}

void put(DList& dl, int val){  //insert a new element with value val at the beginning of the list.

    DListElem* front_elem = new DListElem;
    front_elem ->info = val;
    front_elem -> prev = nullptr;
    front_elem -> next = dl.first;
    dl.first = front_elem;
            
    if(dl.last==NULL) dl.last=dl.first;
}

bool get(DList& dl, int& val){
    /*Removes an item (if possible) from the end of the list. The value of the last 
    element is returned by the val parameter, the memory for the list element 
    is released. The return value indicates whether an item could be retrieved, 
    i.e. it returns false for an empty list and true otherwise.*/
    
    if(dl.last==nullptr) return false;
    if (dl.first==dl.last){             //if there is only 1 element
        val = dl.last -> info;
        DListElem* buffer = new DListElem;
        buffer = dl.last;
        dl.last = nullptr;
        dl.first = nullptr; 
        delete (buffer);
    }
    else{
        val = dl.last -> info;
        DListElem* buffer = new DListElem;
        buffer = dl.last;
        dl.last = dl.last -> prev;
        dl.last -> next = nullptr;         //this part seems to still be the problem
        delete (buffer);
        
    };
    return true;
}

 #include <iostream>
 #include "dlist.h"
 using namespace std;

 int main (int argc, char *argv[])  {

DList queue;
initializeDList (queue);

 for (int i = 1; i <= 5; i++) {
 cout << "put: " << 10 * i << endl; 
 put (queue, 10 * i);
 } 

for (int j = 1; j <= 3; j++){
    int value;    
    if (get (queue, value))
    cout << "     get: " << value << endl;
}

  cin.sync ();
  cin.get ();
  return 0;
  }