C -Segmentation故障！

Question

至少在我看来很奇怪..。程序在我第四次调用enter()函数后运行normally.But，有一个分段错误！如果有任何帮助，我将不胜感激。

使用下面的函数enter()，我想将用户命令的数据添加到一个列表中。

代码的某些部分已经发布在我的另一个问题上，但我认为我应该发布它again...as这是我现在面临的另一个问题。

    /* struct for all the datas that user enters on file*/
typedef struct catalog    
{      char short_name[50];                    
       char surname[50];                       
       signed int amount;                      
       char description[1000];              
       struct catalog *next;
}catalog,*catalogPointer;   

catalogPointer current;
catalogPointer head = NULL; 

void enter(void)    //user command: i <name> <surname> <amount> <description>

{   
    int n,j=2,k=0;
    char temp[1500];
    char *short_name,*surname,*description;
    signed int amount;

    char* params = strchr(command,' ') + 1;  //strchr returns a pointer to the 1st space on the command.U want a pointer to the char right after that space.
    strcpy(temp, params);               //params is saved as temp.

    char *curToken = strtok(temp," ");      //strtok cuts 'temp' into strings between the spaces and saves them to 'curToken'
    printf("temp is:%s \n",temp);

    printf("\nWhat you entered for saving:\n");

    for (n = 0; curToken; ++n)          //until curToken ends:
    {   
        if (curToken)
        {   short_name = malloc(strlen(curToken) + 1);
            strncpy(short_name, curToken, sizeof (short_name));     
        }   
        printf("Short Name: %s \n",short_name);             

        curToken = strtok(NULL," ");                    
        if (curToken)
        {   surname = malloc(strlen(curToken) + 1);
            strncpy(surname, curToken,sizeof (surname));    }   
        printf("SurName: %s \n",surname);

        curToken = strtok(NULL," ");                    
        if (curToken)
        {   //int * amount= malloc(sizeof (signed int *));
            char *chk;                      
            amount = (int) strtol(curToken, &chk, 10);      

            if (!isspace(*chk) && *chk != 0)            
                    fprintf(stderr,"Warning: expected integer value for amount, received %s instead\n",curToken);
        }
        printf("Amount: %d \n",amount);
        curToken = strtok(NULL,"\0");                   
        if (curToken)
        {   description = malloc(strlen(curToken) + 1);
            strncpy(description, curToken, sizeof (description));   
        }
        printf("Description: %s \n",description);
        break;
    }

    if (findEntryExists(head, surname,short_name) != NULL)              //call function in order to see if entry exists already on the catalog
        printf("\nAn entry for <%s %s> is already in the catalog!\nNew entry not entered.\n",short_name,surname);
    else
    {
        printf("\nTry to entry <%s %s %d %s> in the catalog list!\n",short_name,surname,amount,description);
        newEntry(&head,short_name,surname,amount,description);  
        printf("\n**Entry done!**\n");
    }
    // Maintain the list in alphabetical order by surname.


}

catalogPointer findEntryExists (catalogPointer head, char num[],char first[])
{   catalogPointer p = head;
    while (p != NULL && strcmp(p->surname, num) != 0 && strcmp(p->short_name,first) != 0)      
    {   p = p->next;    }
    return p;
}

catalogPointer newEntry (catalog** headRef,char short_name[], char surname[], signed int amount, char description[])
{   
    catalogPointer newNode = (catalogPointer)malloc(sizeof(catalog));
    catalogPointer first;
    catalogPointer second;
    catalogPointer tmp;
    first=head;
    second=NULL;

    strcpy(newNode->short_name, short_name);        
    strcpy(newNode->surname, surname);
    newNode->amount=amount;
    strcpy(newNode->description, description);

    while (first!=NULL)                     
    {       if (strcmp(surname,first->surname)>0)
            second=first;
        else if (strcmp(surname,first->surname)==0)
            {
               if (strcmp(short_name,first->short_name)>0)
                   second=first;
            }
        first=first->next;
    }
    if (second==NULL)
    {       newNode->next=head;
        head=newNode;
    }
    else                             //SEGMENTATION APPEARS WHEN IT GETS HERE!
    {       tmp=second->next;
            newNode->next=tmp;
            first->next=newNode;
    }
}

更新: SegFault只有在进入InsertSort()函数的'else‘循环时才会出现。我观察到，当我尝试将它后面的名称放在列表中时，出现了分段错误。例如，如果列表中存在：

姓名:B姓氏:B金额:6描述:B姓名:D姓氏:D金额:4描述:D姓名:G姓氏:G金额:2描述:G

我输入："x z 77 gege“有一个分段，但如果我输入”x a 77 gege“，它会正常继续……

Answer 1

不能在评论中发帖，所以它是这样的：

  while (first!=NULL)  {  //-> this loop can exit ONLY with 'first' being NULL
    if (strcmp(surname,first->surname)>0)
      second=first;
    else if (strcmp(surname,first->surname)==0)  {
      if (strcmp(short_name,first->short_name)>0)
        second=first;
    }
    first=first->next;
  } 
  if (second==NULL) {       
    newNode->next=head;
    head=newNode;
  }
  else { 
    tmp=second->next;
    newNode->next=tmp;
    first->next=newNode; // first used (but it's NULL!)
  }

换句话说，如果你的程序在循环中找到任何满足条件的条目并设置为'second‘，它就会崩溃。(这会触发“在”列表内部“的预期添加”)。

Ok ~没有时间等待答案:o)，如果你想输入"after“the 'second‘将代码更改为：

  if (second==NULL) {       
    newNode->next=head;
    head=newNode;
  }
  else { 
    newNode->next=second->next;
    second->next=newNode; 
  }

解释(S是'second'，N是'newNode'，A B只是列表中的一些现有条目)：

initial:
       N

  A -> S -> B

first assignment:
       N ---\
            |
            v
  A -> S -> B

second assignment:

       N ---\
       ^    |
       |    v
  A -> S    B

and thus:
  A-> S -> N -> B

Answer 2

不确定是什么导致了这个bug，但我确实看到了这个糟糕的模式：

char *short_name;
short_name = malloc(strlen(curToken) + 1);
strncpy(short_name, curToken, sizeof (short_name));  

sizeof(short_name)将始终是相同的(对于32位平台，通常为4，对于64位平台，通常为8)，因此此处使用的值不正确。你应该做的是：

strncpy(short_name, curToken, strlen(curToken) + 1);

Answer 3

使用像valgrind这样的东西来查找类似这样的问题。