Question

我得到分段错误，而比较struct的成员为0。令人困惑的部分是比较确实发生了几次，然后是粉碎。

请帮忙。代码：

Dword addup(void)
{
  Symbol *curr=NULL;
  Dword ans=0;
  plast->next=NULL;

  if( (phead==NULL) || (plast==NULL) )/*checks that the global pointer to the head & tail is not null.*/
      return 0;

  curr=phead;

  printf("point 1 in addup()********\n");

  for( ; curr!=NULL ; curr=curr->next )
  {

      if(curr!=NULL)
      {

          if(  ((curr->feature.oper)==0)  &&  ((curr->feature.ext)==0)  )/*crash here !*/
          {
              puts("point 2AA in addup()********");

              curr->adess=+IC;
              ans++;
          }
          puts("point 2B in addup()********");
      }

      if((curr->next)==NULL)
          break;
  }


  if(  (curr!=NULL) && (plast!=NULL) )
  {
      if(curr==plast)/*meaning all the list been searched.*/
          return ans;
  }


  return (-1); }

符号：

typedef struct snode  {
    char label[MAXLABEL];

    Dword adess;

    struct
    {
        unsigned int ext:1;
        unsigned int oper:1;
    }feature;

    struct snode *next;
}Symbol;

感谢大家的帮助！

**首先编辑 - phead是指向列表头部的指针。 plast是指向列表的最后一个节点（Symbol）的指针。在其他功能中初始化。 plast-＆gt; next总是为null。（这是在函数的开头 - 因为我想确定）。

**第二次编辑 - 创建功能 -

void csymbl(Dword addess, char *name, Dword ext, Dword ope ){

tempnode.adess=addess;/*tempnode is a global Symbol,that been used to insert new nodes.*/

strcpy(tempnode.label,name);

tempnode.feature.ext=ext;

tempnode.feature.oper=ope;

tempnode.next=NULL;}

将函数连接到列表的函数：

void addsymbol(Symbol a){

if(phead==NULL)/*if phead point to NULL - meaning this is the first symbol been entered & up now the linked list was empty. */
{
    phead=&a;
    plast=phead;
}
else if(plast==phead)/*If plast point to phead,than there is only one symbol in the list(up to now).*/
{
    plast=&a;
    phead->next=plast;
    plast->next=NULL;
}
else
{
    plast->next=&a;
    plast=plast->next;
    plast->next=NULL;
}}

Answer 1

您的addsymbol功能存在非常严重问题，导致 未定义的行为 ：

void addsymbol(Symbol a){
    if(phead==NULL)/*if phead point to NULL - meaning this is the first symbol been entered & up now the linked list was empty. */
    {
        phead=&a;
        plast=phead;
    }
    ...
}

在上面的代码中，如果phead为NULL，则指向本地变量a。

局部变量被称为局部变量，因为它们在它们定义的函数内是局部变量，一旦函数返回局部变量就不再存在。局部变量 lifetime 仅适用于定义它的范围。参数与其他局部变量没有区别。

如果存储指向此类局部变量的指针，则指针将变为无效，当您使用指针时，您将具有未定义的行为。

Answer 2

您没有为第一个元素

初始化next

void addsymbol(Symbol a){

    if(phead==NULL)/*if phead point to NULL - meaning this is the first symbol been entered & up now the linked list was empty. */
    {
        phead=&a;
        plast=phead;

        // unless set it can have any value
        plast->next = NULL;
    }

....
}

此外，你应该将a作为这样的指针传递：

void addsymbol(Symbol* a){

    if(phead==NULL)/*if phead point to NULL - meaning this is the first symbol been entered & up now the linked list was empty. */
    {
        phead=a; // Note this changed - no & operator

正如评论中已经提到的，这里也存在一个问题：

Dword addup(void)
{
  Symbol *curr=NULL;
  Dword ans=0;
  // plast->next=NULL; Don't do it here.... plast may be NULL

  if( (phead==NULL) || (plast==NULL) )/*checks that the global pointer to the head & tail is not null.*/
      return 0;

  plast->next=NULL; // If you really want that code, do it here

最后我想知道你是否真的想要这个：

          curr->adess=+IC;

或者

          curr->adess+=IC;

访问非null结构成员时的分段错误 -

2 个答案: