问题描述
我目前在一所大学就读的程序用C数据结构,我有很多的麻烦现在。我要明确什么我问的帮助不是痕迹,只是练习的挑战问题。
I am currently in a University program studying Data Structures in C and I am having a lot of trouble right now. I want to make clear that what I am asking help for is not for marks, just practice challenge problems.
的目的是实现使用链表堆叠。通过讲义找我想我的大部分功能下降。我需要证明推()和pop()将追加和pretend。使用Cygwin,我没有错误编译。但是当我尝试运行它,我得到一个分段故障。这是什么意思,如何解决?如果我删除堆栈= initLListStack();,错误消失。这里是我的code:
The goal is to implement a stack using Linked Lists. By looking through the lecture notes I think I have most of the functions down. I need to demonstrate Push() and Pop() will an append and a pretend. Using Cygwin, I compiled with no errors. but when I try to run it, I get a "Segmentation Fault". What does this mean and how do I fix it? if I remove "stack = initLListStack();", the error disappears. Here is my code:
#include <stdio.h>
#include <stdlib.h>
typedef struct Link{
int *value;
struct Link *next;
}Link;
typedef struct LList1{
int *size;
Link *head;
}LList1;
typedef struct LListStack{
LList1 *llist;
}LListStack ;
LListStack *initLListStack(void)
{
LListStack *stack = (LListStack *) malloc(sizeof(LListStack)) ;
stack->llist->size = 0;
stack->llist->head = NULL;
return(stack);
}
void removefront(LList1 *llist)
{
if(llist->head != NULL){
llist->head = llist->head->next;
llist->size--;
}
}
Link *FindLastLink(LList1 *llist, Link *link)
{
if(link = NULL){
return(NULL);
}
else if(link->next == NULL){
return(link);
}
else{
return(FindLastLink(llist, link->next));
}
}
Link *FindSecondLastLink(LList1 *llist, Link *link)
{
if(link = NULL){
return(NULL);
}
else if(link->next->next == NULL){
return(link);
}
else{
return(FindSecondLastLink(llist, link->next));
}
}
void removelast(LList1 *llist)
{
Link *secondlastlink = (Link *) malloc(sizeof(Link));
secondlastlink = FindSecondLastLink(llist, llist->head);
secondlastlink->next = NULL;
llist->size--;
}
void prepend(int *newValue, LList1 *templist)
{
Link *node = (Link *) malloc(sizeof(Link));
node->value = newValue;
node->next = templist->head;
templist->head = node;
templist->size++;
}
void append(int *newValue, LList1 *templist)
{
Link *node = (Link *) malloc(sizeof(Link));
Link *lastlink = (Link *) malloc(sizeof(Link));
lastlink = FindLastLink(templist, templist->head);
node->value = newValue;
lastlink->next = node;
node->next = NULL;
templist->size++;
}
void prepush(int *value, LListStack *stack)
{
prepend(value, stack->llist);
}
void apppush(int *value, LListStack *stack)
{
append(value, stack->llist);
}
int prepop(LListStack *stack, int *value)
{
int result ;
if ((!isEmpty(stack)))
{
removefront(stack->llist);
result = 1 ;
}
else {
result = 0 ;
}
return(result) ;
}
int isEmpty(LListStack *stack)
{
int empty;
if (stack->llist->head == NULL)
return( 1 ) ;
else
return( 0 ) ;
}
int apppop(LListStack *stack, int *value)
{
int result ;
if ((!isEmpty(stack)))
{
removelast(stack->llist);
result = 1 ;
}
else
result = 0 ;
return(result) ;
}
//*******MAIN**********//
int main()
{
LListStack *stack = (LListStack *) malloc (sizeof(LListStack));
stack = initLListStack(); //if I take this away, I can run the program
return(0);
}
我没有太多的主要是(),但因为我只是想获得它先运行。初始化堆栈似乎是问题
I don't have that much in Main() yet because I'm just trying to get it to run first. Initializing the Stack seems to be the problem.
感谢您的帮助家伙!
推荐答案
问题是在你的 initLListStack()
功能:
LListStack *stack = (LListStack *) malloc(sizeof(LListStack)) ;
stack->llist->size = 0;
stack->llist->head = NULL;
return(stack);
的malloc
的结果是一个初始化的内存足以容纳块中的 LListStack
结构。
The result of malloc
is an uninitialized block of memory large enough to hold an LListStack
struct.
您与内存做的第一件事就是看它的 LLIST
成员。由于这是未初始化,您可以调用未定义行为,所幸导致段错误。 (编译器将在规范中尴尬的电子邮件发送到发生这种情况时我们的教练。)
The very first thing you do with that memory is read its llist
member. Since this is uninitialized, you invoke undefined behavior which, fortunately, causes a segfault. (The compiler would be within the specification to send embarrassing e-mails to our instructor when this happens.)
您需要初始化 LLIST
才可以使用该成员在堆栈中。是这样的:
You need to initialize llist
before you can use that member in stack. Something like:
LListStack *stack = malloc(sizeof(*stack));
stack->llist = malloc(sizeof(*stack->llist));
stack->llist->size = 0;
stack->llist->head = NULL;
return stack;
请注意,我也去掉了一些不必要的演员和括号,并改变了sizeof操作符来计算,你需要根据你存储到指针的内存。
Note that I've also removed some unnecessary casts and parentheses, and changed the sizeof operator to calculate the memory you need based on the pointer you're storing into.
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