第一次工作正常。我可以添加一个项目,然后用显示功能显示。但是当我尝试添加第二个值时,只要我点击“a”就会出现一个段错误,就在fgets时。我在顶部评论过。
(除了Add,我还没有打扰过其他功能。)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "sortedll.h"
int main(void)
{
int intVal;
LNode *headPtr = NULL;
char buf[BUFLEN];
int result;
do {
// ask the user what they want to do
DisplayMenu();
printf("Please enter a selection: ");
fgets(buf, BUFLEN, stdin);
*buf = toupper(*buf);
switch (*buf)
{
case 'A':
// prompt the user for a value; if we get one, add it to the
// list
printf("Please enter an integer value to add: ");
fgets(buf, BUFLEN, stdin);
//=======================================================================
printf("check"); //doesn't print this second time around. seg fault at fgets?
//=======================================================================
if (1 != sscanf(buf, "%d", &intVal))
{
puts("Error reading the integer value...");
}
else
{
printf("1");
headPtr = AddItem(headPtr, intVal);
}
break;
case 'R':
// if the list is empty display a message; else, get a value
// from the user and attempt to remove it from the list
if (NULL == headPtr)
{
puts("The list is currently empty...");
}
else
{
printf("Please enter an integer value to remove: ");
fgets(buf, BUFLEN, stdin);
if (1 != sscanf(buf, "%d", &intVal))
{
puts("Error reading the integer value...");
}
else
{
headPtr = RemoveItem(headPtr, intVal);
}
}
break;
case 'D':
// display the current contents of the list
result = DisplayList(headPtr);
printf("Currently there %s %d node%s in the list.\n"
, (result != 1) ? "are" : "is"
, result
, (result != 1) ? "s" : "");
break;
case 'Q':
// release all allocated memory and set the head pointer to
// NULL to indicate that it is empty
result = ReleaseMemory(headPtr);
printf("There %s %d node%s released."
, (result != 1) ? "were" : "was"
, result
, (result != 1) ? "s" : "");
headPtr = NULL;
break;
default:
puts("Unrecognized option; please try again.");
break;
}
puts(" ");
} while ('Q' != *buf);
puts("Thanks for playing! Bye!!\n");
return 0;
} // end of "main"
// ==== AddItem ===============================================================
LNode* AddItem(LNode *headPtr, int newItem)
{
LNode *node = malloc(sizeof(*node));
node->value = newItem;
if(headPtr == NULL)
{
node->next = NULL;
return node;
}
LNode *leadPtr = headPtr;
LNode *trailPtr = headPtr;
while(leadPtr->value != newItem)
{
leadPtr = leadPtr->next;
trailPtr = leadPtr;
}
leadPtr = leadPtr->next;
free(trailPtr->next);
trailPtr->next = node;
node->next = leadPtr;
return headPtr;
} // end of "AddItem"
// ==== DisplayList ===========================================================
int DisplayList(LNode *nodePtr)
{
auto int counter = 0;
// if the list is empty, indicate as such and return zero
if (NULL == nodePtr)
{
puts("The list is currently empty...");
return (0);
}
while (NULL != nodePtr)
{
printf("%d\n", nodePtr->value);
nodePtr = nodePtr->next;
counter++;
}
return (counter);
} // end of "DisplayList"
// ==== DisplayMenu ===========================================================
void DisplayMenu(void)
{
puts("A)dd a value");
puts("R)emove a value");
puts("D)isplay the list");
puts("Q)uit");
} // end of "DisplayMenu"
// ==== ReleaseMemory =========================================================
int ReleaseMemory(LNode *headPtr)
{
} // end of "ReleaseMemory"
// ==== RemoveItem ============================================================
LNode* RemoveItem(LNode *headPtr, int targetItem)
{
} // end of "RemoveItem"
答案 0 :(得分:0)
当leadPtr可能为NULL时,您似乎试图访问leadPtr-&gt;值。
while(leadPtr->value != newItem)
{
leadPtr = leadPtr->next;
trailPtr = leadPtr;
}
在尝试访问其成员之前,您需要确保leadPtr!= NULL。
我建议您重构代码片段所属的功能,在内存访问方面看起来有点脆弱。
答案 1 :(得分:0)
你真的应该检查malloc调用的返回值:
LNode * node = malloc(sizeof(* node));
node-&gt; value = newItem;
如果你的堆空间不足会怎么样?