我无法弄清楚为什么我的代码会中断。除了我试图反转链表时，每件事都有效。它“停止工作”。 （这个函数; void reverseList（struct produceItem ** inHead））有什么想法吗？我已经坚持了一段时间了。我认为问题可能是它在某些地方没有读取NULL，但我无法弄明白。
#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
struct produceItem{
char produce[20];
char type[20];
char soldBy[20];
float price;
int quantityInStock;
struct produceItem *next;
};
struct produceItem* append(struct produceItem *inHead, char *nextProduce, char *nextType, char *nextSoldBy, char *nextPrice, char *nextQuantityInStock){
struct produceItem *temp;
temp =(struct produceItem *)malloc(sizeof(struct produceItem));
strcpy(temp->produce, nextProduce);
strcpy(temp->type, nextType);
strcpy(temp->soldBy, nextSoldBy);
temp->price = atof(nextPrice);
temp->quantityInStock = atoi(nextQuantityInStock);
if(inHead == NULL){
inHead = temp;
temp->next = NULL;
}
else{
temp->next = inHead;
inHead = temp;
}
return inHead;
}
struct produceItem* readData(struct produceItem *inHead){
const char comma[2] = ",";
char *produceTemp;
char *typeTemp;
char *soldByTemp;
char *priceTemp;
char *quantityInStockTemp;
char dataLine[100];
char fileName[] = "AssignmentTwoInput.txt";
FILE *inputFile;
printf("\nFile %s has been read.\n\n", fileName);
inputFile = fopen(fileName, "r");
if( inputFile == NULL){
printf("%sList Does not exist\n", fileName);
return;
}
while((fgets(dataLine, 100, inputFile)) != NULL){
produceTemp = strtok(dataLine, comma);
typeTemp = strtok(NULL, comma);
soldByTemp = strtok(NULL, comma);
priceTemp = strtok(NULL, comma);
quantityInStockTemp = strtok(NULL, comma);
inHead = append(inHead, produceTemp,typeTemp,soldByTemp,priceTemp,quantityInStockTemp);
}
fclose(inputFile);
return inHead;
}
void display(struct produceItem *inHead){
int i = 1;
if(inHead == NULL){
printf("List does not exist.\n");
return;
}
printf("=========================================================================\n");
printf("Item # Produce Type Sold By Price In Stock\n");
printf("==========================================================================\n");
for(i=1; i<27; i++){
//while(inHead != NULL){
printf("\n%5d", i);
printf(" %-12s ", inHead->produce);
printf("%-16s ", inHead->type);
printf("%-16s ", inHead->soldBy);
printf("%3.2f ", inHead->price);
printf("%8d", inHead->quantityInStock);
inHead = inHead->next;
//i++;
}
printf("\n\n");
}
exportData(struct produceItem *n){
char fileName[] = "AssignmentTwoOutput.txt";
FILE *exportFile;
int i =1;
if(n == NULL){
printf("List does not exist.\n");
return;
}
exportFile = fopen(fileName, "w");
//printf("hi");
fprintf(exportFile,"================================================================\n");
//printf("hi");
fprintf(exportFile,"Item# Produce Type Sold By Price In Stock\n");
fprintf(exportFile,"================================================================\n");
for(i=1; i<27; i++){
//while(n->next != NULL){
//printf("hi");
fprintf(exportFile,"\n%3d", i);
fprintf(exportFile," %-12s ", n->produce);
fprintf(exportFile,"%-15s ", n->type);
fprintf(exportFile,"%-15s ", n->soldBy);
fprintf(exportFile,"%3.2f ", n->price);
fprintf(exportFile,"%8d", n->quantityInStock);
n = n->next;
}
printf("\nYour data has been written to AssignmentTwoOutput.txt, thank you.\n\n");
fclose(exportFile);
}
//void recursiveReverse(struct node** head_ref)
//{
//struct node* first;
// struct node* rest;
/* empty list */
// if (*head_ref == NULL)
//return;
/* suppose first = {1, 2, 3}, rest = {2, 3} */
//first = *head_ref;
//rest = first->next;
/* List has only one node */
//if (rest == NULL)
//return;
/* reverse the rest list and put the first element at the end */
//recursiveReverse(&rest);
//first->next->next = first;
/* tricky step -- see the diagram */
//first->next = NULL;
/* fix the head pointer */
//*head_ref = rest;
//}
void reverseList(struct produceItem** inHead){
//printf("1");
struct produceItem* first;
struct produceItem* follow;
//printf("2");
if (*inHead==NULL){
// printf("3");
printf("List does not exist.\n");
return;}
first = *inHead;
//printf("4");
follow = first->next;
if(follow==NULL)
//printf("5");
return;
reverseList(&follow);
first->next->next = first;
first->next = NULL;
*inHead = follow;
}
int main (void){
int choice;
struct produceItem *head;
while(1){
printf("List of Operations\n");
printf("===============\n");
printf("1. Stock Produce Department\n");
printf("2. Display Produce Inventory\n");
printf("3. Reverse Order of Produce Inventory\n");
printf("4. Export Produce Inventory\n");
printf("5. Exit\n");
printf("Enter you choice: ");
scanf("%d", &choice);
if(choice <= 0 || choice > 5){
printf("Enter a valid response please: \n");
exit(0);
}
switch(choice){
case 1:
//reading from thefile
head = readData(head);
break;
case 2:
//displays the list
display(head);
break;
case 3:
//reverse the list
reverseList(&head);
break;
case 4:
exportData(head);
break;
case 5:
//Exits the operation
printf("Exiting, Thank you.");
exit(0);
break;
}
}
}
答案 0 :(得分：1)
在这个递归函数中：
void reverseList(struct produceItem** inHead){
//printf("1");
struct produceItem* first;
struct produceItem* follow;
//printf("2");
if (*inHead==NULL){
// printf("3");
printf("List does not exist.\n");
return;}
first = *inHead;
//printf("4");
follow = first->next;
if(follow==NULL)
//printf("5");
return;
reverseList(&follow);
first->next->next = first;
first->next = NULL;
*inHead = follow;
}
此函数将以递归方式在列表中运行。
好的，看看你的代码：
请注意，在这个阶段实际上什么也没发生过。 这意味着您的处理（函数末尾的行）将以列表的相反顺序发生。从后到前。 这似乎对你想做的事情是正确的。
下一行：
first->next->next = first;
这似乎是正确的，因为它会设置下一个＆＃34;跟随＆＃34;节点指向这一个。在改变列表中下一个指针的方向时。
现在你有了这一行：
first->next = NULL;
请记住，我们已经说过你的＆＃34;处理＆＃34;节点将以相反的顺序发生。因此，您将逐个有效地将所有下一个指针设置为NULL。我认为哪个会完全断开你的队列？
我理解的最后一行只是让你找到队列的新头指针，这似乎很好。
通过递归来做这种算法通常是一个坏主意。 如果您的列表变长，您很容易导致堆栈溢出问题。 此外，如果由于某种原因您的列表有问题而且它是循环的，那么很难检测到它并且不会导致问题。 通常在性能方面，这种类型的递归算法将比仅适当的循环实现慢。伪代码＆＃34;反向＆＃34;列表：
reverseList(** head)
{
current = head
prev = null
next = null
int i = 0;
while (current)
{
next = current->next;
current->next = prev;
prev = current;
current = next;
i++;
if (i > MAX) reportError();
}
head = prev;
}