c - 为什么在我的双向链表中发生段错误(核心转储)？

Question

因此，从我从其他段错误中读到的内容来看，它涉及访问您不应该访问的内存(坏内存，或者没有使用 malloc())。出于某种原因，当我创建 2 个节点时没有出现段错误，但其他任何节点都会出现段错误。如果有人可以解释一下我在这个程序中哪里出了问题，那将非常有帮助。谢谢。

    #include "header.h"
    #include <stdlib.h>
    #include <stdio.h>
    #include <math.h>
    int main(int argc, char *argv[]) {

        int N; 
        //int oddsonly = (BITS_PER_SEG*2) - 1; 
        int NSegs;
        int numOfPrimes;

        if (argc == 2) sscanf(argv[1],"%d",&N);
            else scanf("%d",&N);
            NSegs = (int)ceil(N/(float)odds_only);
            printf("This is the number of segments made: %d\n", NSegs);
        //this is how we make a doubly linked list 
        //void makelinkedlist(){
        //this is how we make a doubly linked list 
        //void makelinkedlist(){
        int i; 
        seg *node; 
        seg *current;
        //head = (seg*)malloc(sizeof(seg));
        head = NULL;
        for(i = 1; i < NSegs; i++ ) { 
            if(i == 1) {
                node = (seg*)malloc(sizeof(seg)); 

                node->prev = NULL; 
                node->next = NULL;
                head = node;
            }//if
            else{
                current = (seg*)malloc(sizeof(seg)); 
                current = head; 
                while(current->next != NULL){
                    current = current->next; 
                }//while
                node = current->next; 
                node->prev = current; 
                node->next = NULL;    
                }//else
            }//for
        printf("Done allocating %d nodes\n",i); '

我的头文件有这个:

    #ifndef EXTERN
    #define EXTERN extern
    #endif

    #define SIZE_OF_SEG      256       // 256 int per segment
    #define odds_only   16383
    #define BITS_PER_SEG     (8*SIZE_OF_SEG*sizeof(int))


    typedef struct _seg {  /* definition of new type "seg" */
        int  bits[256];
        struct _seg  *next,*prev;        
          }seg  ;

    EXTERN int NSegs;

    EXTERN seg *head;             // This variable will point to the 
                          // start of the linked list of segments !!!

    //EXTERN void clearAll( );            // Uses head to find the "bit array" (list)
    EXTERN void sieveOfE( int N );      // Uses head to find the "bit array" (list)
    EXTERN int  countPrimes( int N );   // Uses head to find the "bit array" (list)
    EXTERN void printPrimes( int N );   // Uses head to find the "bit array" (list)

Answer 1

在您的 for 循环中，在第一次迭代中 head 被设置为一个新节点。在第二次迭代中，做了一些奇怪的事情:

current = (seg*)malloc(sizeof(seg)); 
current = head; 

现在您已经分配了一些空间，但是您已经覆盖了指向它的指针(这是内存泄漏)。之后就出错了:

while(current->next != NULL){
    current = current->next; 
}//while

node = current->next; 
node->prev = current; 

此处，node 设置为 NULL，因此您要写入空地址，因此是核心转储。