c - 指针值改变

Question

输入文件:

JOHN 9999999999
MEENA 9888888888
RIA 8718218218
SONIA 7777777777
FINCH 1234567890

• 我想通过将文件内容追加到列表中来创建一个循环链表。我创建了一个带有“NO VALUE”条目的哨兵。

• 当我在 gdb 中测试我的代码时，在 uploadAddresses() 中 while 循环结束时的 p->next->name 显示 Finch。这怎么可能？p 值保持不变，只有临时值在之后发生变化每次迭代。

  #include<stdio.h>    
  #include<stdlib.h>    
  #include<string.h>    
  #define MAXPHONENO 100
  
  //Variables declaration 
  struct Contact {
    char *name;
    char *mobileno;
    struct Contact *next;
  };
  typedef struct Contact Contact;    
  typedef Contact* PHBOOK;
  
  //Function declaration
  PHBOOK createAddressBook();
  PHBOOK uploadAddresses(PHBOOK pb,char *name);
  
  //Implementation
  PHBOOK createAddressBook(){    
    PHBOOK pb = (PHBOOK)malloc(sizeof(Contact));   
    pb->name = "NO ENTRY";    
    pb->mobileno = "NO ENTRY";    
    pb->next = pb;    
    return pb;    
  }
  
  
  PHBOOK uploadAddresses(PHBOOK p,char *fname){
    PHBOOK temp = p;
    char mob[20],name[20];
    FILE *fp = fopen(fname,"r");
    while(fscanf(fp,"%s %s",name,mob)!=EOF){
      temp->next = (PHBOOK)malloc(sizeof(Contact));    
      temp = temp->next;    
      temp->name = name;    
      temp->mobileno = mob;    
      printf("%s %s\n",name,mob);    
    }    
    temp->next = p;    
    return p;    
  }   
  
  int main(){    
    PHBOOK pb = createAddressBook();    
    pb = uploadAddresses(pb,"/home/user/names_mobile");    
    return 0;
  }
  

Answer 1

改变:

temp->name = name;
temp->mobileno = mob;    

收件人:

temp->name = malloc(strlen(name)+1);
temp->mobileno = malloc(strlen(mob)+1);
strcpy(temp->name,name);
strcpy(temp->mobileno,mob);