我在修改链表成员时遇到问题。我们有一个结构“记录”，声明如下：
typedef struct record
{
char *make;
int year;
int stock;
struct record *next;
} Record;
保存有关经销商汽车的信息。
我们首先使用来自 CLI 参数指示的文本文件的输入创建链接列表，该文件与此完全相同：
Ford 2012 15
Ford 2011 3
Ford 2010 5
Toyota 2011 7
Toyota 2012 20
Toyota 2009 2
Honda 2011 9
Honda 2012 3
Honda 2013 12
Chevrolet 2013 10
Chevrolet 2012 25
这些值使用 fgets 读入变量，然后发送到“insertRecordInAsendingOrder”函数，然后调用“createRecord”来实际创建链表中的每条记录。然后 insertRecordInAscendingOrder 将记录放入列表中的适当位置。然后使用函数“printList”按排序顺序打印出原始列表。
从这里开始，我们继续更新链表成员之一的股票。值“Ford”（代表品牌）、“2012”（代表年份）和“12”（代表 newStock 字段）被硬编码到函数“Main”中，并被发送到“updateStockOfCar”函数，这是以下代码：
int updateStockOfCar(Record *head, char *make, int year, int newStock)
{
if(head == NULL)
{
printf("The list is empty\n");
return 0;
}
Record * matching = malloc(sizeof(Record));
matching->make = make;
matching->year = year;
//If the first record is the one we want to modify, then do so
if(strcmp(head->make, matching->make) == 0)
{
if(head->year == matching->year)
{
head->stock = newStock;
return 1;
}
Record* previous = head;
Record* current = head->next;
//Loop through the list, looking for the record to update
while(current != NULL)
{
if(strcmp(current->make, matching->make) == 0 && current->year == matching->year)
{
current->stock = newStock;
return 1;
}
else
{
previous = current;
current = current -> next;
}
}
}
return 0;
}
如您所见，此函数接受列表的头节点（我们开始搜索要更新的正确节点的位置）、品牌和年份（针对我们要修改库存的节点）和 newStock (我们将用于替换目标节点中标准“库存”字段的值）。
我们的第一种情况是如果 head 为 NULL，在这种情况下，我们说列表是空的并且返回一个不成功的“0”返回给“Main”中的调用变量。
我们的第二种情况是如果匹配中head中的make字段之间的strcmp相同，并且head和matching中的年份字段相同，那么我们将head的stock字段更新为newStock并返回成功的“1”返回funciton“主要的”。本质上，如果头节点是要修改的正确节点，我们就会这样做。
我们的第三种情况是如果头节点不是要修改的正确节点。在 current（定义为开头的开头）不为 NULL 的情况下，我们将当前节点的 make 和 year 字段与我们想要更改的目标节点进行比较。如果它们匹配，我们将 current 的 stock 字段设置为 newStock 并返回成功的“1”。如果它们不匹配，我们将通过“else”条件，遍历列表，直到找到我们正在寻找的那个，在这种情况下，我们更新 current 的 stock 字段。
如果所有这些情况都失败，则出现第四种情况，将不成功的“0”返回到 main，表示目标记录不存在于链表中。
但是，当编译并执行代码（我在下面为您提供的）时，会为程序的输出生成以下内容：
The original list in ascending order:
--------------------------------------------------
Make Year Stock
--------------------------------------------------
Chevrolet 2012 25
Chevrolet 2013 10
Ford 2010 5
Ford 2011 3
Ford 2012 15
Honda 2011 9
Honda 2012 3
Honda 2013 12
Toyota 2009 2
Toyota 2011 7
Toyota 2012 20
====Update Stock of Car====
Failed to update stock. Please make sure the car that has the make/year exists in the list.
====Removing a Record====
I'm trying to remove the record of Ford 2012...
Removed the record successfully. Printing out the new list...
--------------------------------------------------
Make Year Stock
--------------------------------------------------
Chevrolet 2012 25
Chevrolet 2013 10
Ford 2010 5
Ford 2011 3
Honda 2011 9
Honda 2012 3
Honda 2013 12
Toyota 2009 2
Toyota 2011 7
Toyota 2012 20
====Insert Record in Ascending Order====
I'm trying to insert a record of make Jeep year 2011 stock 5...
Inserted the record successfully. Printing out the new list...
--------------------------------------------------
Make Year Stock
--------------------------------------------------
Chevrolet 2012 25
Chevrolet 2013 10
Ford 2010 5
Ford 2011 3
Honda 2011 9
Honda 2012 3
Honda 2013 12
Jeep 2011 5
Toyota 2009 2
Toyota 2011 7
Toyota 2012 20
I'm trying to insert a record of make Honda, year 2012, and stock 10...
Inserted the record successfully. Printing out the new list...
--------------------------------------------------
Make Year Stock
--------------------------------------------------
Chevrolet 2012 25
Chevrolet 2013 10
Ford 2010 5
Ford 2011 3
Honda 2011 9
Honda 2012 10
Honda 2012 3
Honda 2013 12
Jeep 2011 5
Toyota 2009 2
Toyota 2011 7
Toyota 2012 20
出于某种原因，“Main”函数被告知找不到节点，即使它存在于列表中。
这是整个程序，虽然还有更多有问题的功能，但我已经排除了其中的大部分：
/*homework2stackoverflow2.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LINE 50
#define MAX_MAKE 20
typedef struct record
{
char *make;
int year;
int stock;
struct record *next;
} Record;
int compareCars(Record *car1, Record *car2);
void printList(Record *head);
Record* createRecord(char *make, int year, int stock);
int insertRecordInAscendingOrder(Record **head, char *make, int year, int stock);
int removeRecord(Record **head, char *make, int year);
int updateStockOfCar(Record *head, char *make, int year, int newStock);
int main(int argc, char **argv)
/*START MAIN*/
{
FILE *inFile = NULL;
char line[MAX_LINE + 1];
char *make, *yearStr, *stockStr;
int year, stock, len;
Record* headRecord = NULL;
/*Input and file diagnostics*/
if (argc!=2)
{
printf ("Filename not provided.\n");
return 1;
}
if((inFile=fopen(argv[1], "r"))==NULL)
{
printf("Can't open the file\n");
return 2;
}
/*obtain values for linked list*/
while (fgets(line, MAX_LINE, inFile))
{
make = strtok(line, " ");
yearStr = strtok(NULL, " ");
stockStr = strtok(NULL, " ");
year = atoi(yearStr);
stock = atoi(stockStr);
insertRecordInAscendingOrder(&headRecord,make, year, stock);
}
/*START PRINT ORIGINAL LIST*/
printf("The original list in ascending order: \n");
printList(headRecord);
/*END PRINT ORIGINAL LIST*/
/*START UPDATE STOCK TEST*/
printf("\n====Update Stock of Car====\n");
int newStock = 12;
char* newMake = "Ford";
int updateStatus = updateStockOfCar(headRecord, newMake, year, newStock);
if(updateStatus == 0)
{
printf("Failed to update stock. Please make sure the car that has the make/year exists in the list.\n");
}
if(updateStatus == 1)
{
printf("Updated stock successfully. Printing out the new list...\n");
printList(headRecord);
}
/*END UPDATE STOCK TEST*/
/*START REMOVE RECORD TEST*/
printf("\n====Removing a Record====\n");
char *deleteMake = "Ford";
int deleteYear = 2012;
int removeStatus = removeRecord(&headRecord, deleteMake, deleteYear);
if(removeStatus == 0)
{
printf("Failed to remove the record. Please make sure the care that has the make/year exists in the list.\n");
}
if(removeStatus == 1)
{
printf("Removed the record successfully. Printing out the new list...\n");
printList(headRecord);
}
/*END REMOVE RECORD TEST*/
/*START INSERT IN ASCENDING ORDER TEST*/
printf("\n====Insert Record in Ascending Order====\n");
char* insertMake = "Jeep";
int insertYear = 2011;
int insertStock = 5;
int insertStatus = insertRecordInAscendingOrder(&headRecord, insertMake, insertYear, insertStock);
printf("I'm trying to insert a record of make %s year %d stock %d...\n", insertMake, insertYear, insertStock);
if(insertStatus == 0)
{
printf("Failed to insert the new record. Please make sure the car that has the make/year doesn't exist in the list.\n");
}
if(insertStatus == 1)
{
printf("Inserted the record successfully. Printing out the new list...\n");
printList(headRecord);
}
insertMake = "Honda";
insertYear = 2012;
insertStock = 10;
insertStatus = insertRecordInAscendingOrder(&headRecord, insertMake, insertYear, insertStock);
printf("\nI'm trying to insert a record of make %s, year %d, and stock %d...\n", insertMake, insertYear, insertStock);
if(insertStatus == 0)
{
printf("Failed to insert the new record. Please make sure the car that has the make/year doesn't exist in the list.\n");
}
if(insertStatus == 1)
{
printf("Inserted the record successfully. Printing out the new list...\n");
printList(headRecord);
}
/*END INSERT IN ASCENDING ORDER TEST*/
fclose(inFile);
return 0;
}
/*END MAIN*/
int compareCars(Record *car1, Record *car2)
{
int makecmp = strcmp(car1->make, car2->make);
if( makecmp > 0 )
return 1;
if( makecmp == 0 )
{
if (car1->year > car2->year)
{
return 1;
}
if( car1->year == car2->year )
{
return 0;
}
return -1;
}
/*prints list. lists print.*/
void printList(Record *head)
{
int i;
int j = 50;
Record *aRecord;
aRecord = head;
for(i = 0; i < j; i++)
{
printf("-");
}
printf("\n");
printf("%20s%20s%10s\n", "Make", "Year", "Stock");
for(i = 0; i < j; i++)
{
printf("-");
}
printf("\n");
while(aRecord != NULL)
{
printf("%20s%20d%10d\n", aRecord->make, aRecord->year,
aRecord->stock);
aRecord = aRecord->next;
}
printf("\n");
}
Record* createRecord(char *make, int year, int stock)
{
Record *theRecord;
int len;
if(!make)
{
return NULL;
}
theRecord = malloc(sizeof(Record));
if(!theRecord)
{
printf("Unable to allocate memory for the structure.\n");
return NULL;
}
theRecord->year = year;
theRecord->stock = stock;
len = strlen(make);
theRecord->make = malloc(len + 1);
strncpy(theRecord->make, make, len);
theRecord->make[len] = '\0';
theRecord->next=NULL;
return theRecord;
}
int insertRecordInAscendingOrder(Record **head, char *make, int year, int stock)
{
Record *previous = *head;
Record *newRecord = createRecord(make, year, stock);
int compResult;
Record *current = *head;
if(*head == NULL)
{
*head = newRecord;
//printf("Head is null, list was empty\n");
return 1;
}
else if(compareCars(newRecord, *head) == 0)
{
return 0;
}
else if ( compareCars(newRecord, *head)==-1)
{
*head = newRecord;
(*head)->next = current;
//printf("New record was less than the head, replacing\n");
return 1;
}
else
{
//printf("standard case, searching and inserting\n");
previous = *head;
while ( current != NULL &&(compareCars(newRecord, current)==1))
{
previous = current;
current = current->next;
}
previous->next = newRecord;
previous->next->next = current;
}
return 1;
}
int removeRecord(Record **head, char *make, int year)
{
printf("I'm trying to remove the record of %s %d...\n", make, year);
if(*head == NULL)
{
printf("The list is empty\n");
return 0;
}
Record * delete = malloc(sizeof(Record));
delete->make = make;
delete->year = year;
//If the first record is the one we want to delete, then we need to update the head of the list and free it.
if((strcmp((*head)->make, delete->make) == 0))
{
if((*head)->year == delete->year)
{
delete = *head;
*head = (*head)->next;
free(delete);
return 1;
}
}
Record * previous = *head;
Record * current = (*head)->next;
//Loop through the list, looking for the record to remove.
while(current != NULL)
{
if(strcmp(current->make, delete->make) == 0 && current->year == delete->year)
{
previous->next = current->next;
free(current);
return 1;
}
else
{
previous = current;
current = current->next;
}
}
return 0;
}
int updateStockOfCar(Record *head, char *make, int year, int newStock)
{
if(head == NULL)
{
printf("The list is empty\n");
return 0;
}
Record * matching = malloc(sizeof(Record));
matching->make = make;
matching->year = year;
//If the first record is the one we want to modify, then do so
if(strcmp(head->make, matching->make) == 0)
{
if(head->year == matching->year)
{
head->stock = newStock;
return 1;
}
Record* previous = head;
Record* current = head->next;
//Loop through the list, looking for the record to update
while(current != NULL)
{
if(strcmp(current->make, matching->make) == 0 && current->year == matching->year)
{
current->stock = newStock;
return 1;
}
else
{
previous = current;
current = current -> next;
}
}
}
return 0;
}
是什么导致这件事表明它不在列表中？
是的......这是一个家庭作业：P