[英]linked list segmentation fault. I'm guessing I'm doing something wrong with pointers here
EDIT: Heres the updated insert code. 编辑:这是更新的插入代码。 I'll try asserting it, but see if I'm still making a mistake
我会尝试断言,但是看看我是否仍在犯错
bool SortedList::insert(Student *s){
bool inList = false;
// create an iterator for the list
ListNode *current = head;
// create a new ListNode for the student to be added
ListNode *addition = new ListNode();
// initialize addition to the student and the next to NULL
addition->student = s;
addition->next = NULL;
//while current is not at the end of the list
while(current != NULL){
// if the iteration's ID is equal to the given ID return
// false and delete the ListNode addition
if(current->student->getID() == addition->student->getID()){
delete addition;
return false;
// else if the next student ID in the list is greater than
// the given ID break the while loop
}else if(current->next != NULL && current->next->student->getID() > addition->student->getID()){
inList = true;
break;
}
// otherwise set current to the next student in the list
current = current->next;
}
// if current is at the end of the list and student wasn't found, set
// current next to addition
if(!inList){
current->next = addition;
// else set addition next to current next next and current next to addition
}else{
addition->next = current->next;
current->next = addition;
}
// return true regardless as the student has been added
return true;
}
I've been having some trouble with this basic linkedlist.cpp file I've been working on. 我一直在使用这个基本的linkedlist.cpp文件遇到麻烦。 I'm guessing that I'm probably using the pointers wrong or something along those lines.
我猜想我可能使用了错误的指针或类似的东西。 The main file is given as an object file so I can't look at it and for some reason I only thought to test the insert method(I'm extremely low on sleep and struggling).
主文件是作为目标文件提供的,所以我看不到它,由于某种原因,我只考虑测试insert方法(我的睡眠和挣扎状况极低)。 Anyways I'm guessing somewhere in the insert method I'm referencing NULL wrong, but I can't figure out where.
无论如何,我猜在insert方法的某个地方我错误地引用了NULL,但是我不知道在哪里。
ERROR: Segmentation fault(core dumped) NOTE: this error occured after running the insert 错误:分段错误(核心已转储)注:运行插入后发生此错误
#include <iostream>
#include "SortedList.h"
using namespace std;
/**
* zero argument constructor - initializes an empty list
*/
SortedList::SortedList() : head(NULL){}
/**
* If a student with the same ID is not already in the list, inserts
* the given student into the list in the appropriate place and returns
* true. If there is already a student in the list with the same ID
* then the list is not changed and false is returned.
*
* @param *s a given pointer to a student
* @return boolean value based on whether the student was inserted or not
*/
bool SortedList::insert(Student *s){
// create an iterator for the list
ListNode *current = head;
// create a new ListNode for the student to be added
ListNode *addition = new ListNode();
// initialize addition to the student and the next to NULL
addition->student = s;
addition->next = NULL;
//while current is not at the end of the list
while(current != NULL){
// if the iteration's ID is equal to the given ID return
// false and delete the ListNode addition
if(current->student->getID() == addition->getID()){
return false;
delete addition;
// else if the next student ID in the list is greater than
// the given ID break the while loop
}else if(current->next->student->getID() > addition->getID()){
break;
}
// otherwise set current to the next student in the list
current = current->next;
}
// if current is at the end of the list and student wasn't found, set
// current next to addition
if(current == NULL){
current->next = addition;
// else set addition next to current next next and current next to addition
}else{
addition->next = current->next->next;
current->next = addition;
}
// return true regardless as the student has been added
return true;
}
/**
* Searches the list for a student with the given student ID. If the
* student is found, it is returned; if it is not found, NULL is returned.
*
* @param studentID the given studentID to find in the list
* @return a pointer to a the student found or NULL if the student isn't found
*/
Student * SortedList::find(int studentID){
// create iterator for the list
ListNode *current = head;
// while not at the end of the list iterate
while(current != NULL){
// if the current student ID equals the given student ID return
// the student
if(current->student->getID() == studentID){
return current->student;
}
// otherwise continue iterating
current = current->next;
}
// if not found then return NULL
return NULL;
}
/**
* Searches the list for a student with the given student ID. If the
* student is found, the student is removed from the list and returned;
* if no student is found with the given ID, NULL is returned.
*
* @param studentID the given student ID to be removed from the list
* @return a pointer to the student that was removed or NULL if the student
* wasn't found
*/
Student * SortedList::remove(int studentID){
// create iterator for the list
ListNode *current = head;
// create the to hold the value ahead of the iterator
ListNode *currentNext;
// create to hold the removed student
Student *remove;
// while current is not at the end of the list iterate
while(current != NULL){
// set currentNext to the value ahead of iterator
currentNext = current->next;
// if its ID equals the given ID
if(currentNext->student->getID() == studentID){
// set remove to the student removing
remove = currentNext->student;
// set current next to currentNext next
// (current next next)
current->next = currentNext->next;
//delete the removed ListNode
delete currentNext;
//return the removed student
return remove;
}
}
//if the student wasn't found return NULL
return NULL;
}
/**
* Prints out the list of students to standard output. The students are
* printed in order of student ID (from smallest to largest), one per line
*/
void SortedList::print() const{
//create iterator for list
ListNode *current = head;
//while current is not at the end of the list iterate
while(current != NULL){
// print each individual student and end line
current->student->print();
cout << endl;
//iterate the list
current = current->next;
}
}
while(current != NULL){
// if the iteration's ID is equal to the given ID return
// false and delete the ListNode addition
if(current->student->getID() == addition->getID()){
2 return false;
delete addition;
// else if the next student ID in the list is greater than
// the given ID break the while loop
1 }else if(current->next->student->getID() > addition->getID()){
break;
}
At the line I marked 1, you dereference current->next
without ever checking if it is NULL
or not. 在我标记为1的那一行中,您取消引用
current->next
而不检查它是否为NULL
。 Also, at the line I marked 2, you end exectution, and then delete the pointer. 同样,在我标记为2的行上,您结束执行, 然后删除指针。 You should
delete
before you return
. 您应该先
delete
然后再return
。
if(current == NULL){
3 current->next = addition;
// else set addition next to current next next and current next to addition
}else{
4 addition->next = current->next->next;
current->next = addition;
}
At the line marked 3, you dereference current
only if it's NULL
. 在标记为3的行中,仅当
current
NULL
时才取消引用。 Bad juju. 坏枣 At the line marked 4, you dereference
current->next
without checking if it's NULL
first. 在标记为4的行中,取消引用
current->next
而不先检查它是否为NULL
。 I think you meant to set addition->next
to current->next
anyway. 我认为您无论如何都要将“
addition->next
设置为“ current->next
。
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