c - 按升序插入记录函数 - C 作业

Question

美好的一天，Stack Overflow。

我有一个家庭作业要在这个周末完成，但我遇到了一些问题。我们有一个结构“Record”(其中包含有关经销商汽车的信息)，它根据 1)其品牌和 2)根据其型号年份放置在链接列表中的特定位置。

这是在最初构建列表时完成的，当在 Main 中调用“int insertRecordInAscendingOrder”函数时。在“insertRecordInAscendingOrder”中，调用了第三个函数“createRecord”，其中创建了链表。该函数然后转到函数“compareCars”以确定将哪些元素放在哪里。根据此函数返回的值，insertRecordInAscendingOrder 然后将记录放在它所属的位置。然后打印出该列表。任务还有很多，但我会在完成任务时跨过那座桥。

理想情况下，为了使分配被认为是正确的，链表必须按以下方式排序:

    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 2013 20

来自一个文本文件，其中的数据按以下方式排序:

    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

请注意，“制造”字段的字母顺序优先，然后，型号年份从旧到新排列。

但是，该程序将其生成为最终列表:

    Chevrolet 2012 25
    Chevrolet 2013 10
    Honda 2011 9
    Honda 2012 3
    Honda 2013 12
    Toyota 2009 2
    Toyota 2011 7
    Toyota 2012 20
    Ford 2010 5
    Ford 2011 3
    Ford 2012 15

昨天我和一名研究生坐下来试图解决所有这些问题，但我们就是无法弄清楚为什么它将福特节点踢到列表的末尾。

这是代码。您会注意到，我在插入节点的每个实例中都包含了一个 printList 调用。这样，您就可以看到节点按“顺序”放置时发生了什么。它在 ANSI C99.所有函数调用都必须按照指定的方式进行，因此不幸的是，没有真正的方法可以通过创建更高效​​的算法来解决这个问题。

    #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 main(int argc, char **argv)
{
    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);

    }


    printf("The original list in ascending order: \n");
    printList(headRecord);
}

/*use strcmp to compare two makes*/

int compareCars(Record *car1, Record *car2)
{
    int compStrResult;
    compStrResult = strcmp(car1->make, car2->make);
    int compYearResult = 0;

    if(car1->year > car2->year)
    {
        compYearResult = 1;
    }
    else if(car1->year == car2->year)
    {
        compYearResult = 0;
    }
    else
    {
        compYearResult = -1;
    }

    if(compStrResult == 0 )
    {
        if(compYearResult == 1)
        {
            return 1;
        }
        else if(compYearResult == -1)
        {
            return -1;
        }
        else
        {
            return compStrResult;
        }
    }
    else if(compStrResult == 1)
    {
        return 1;
    }
    else
    {
        return -1;
    }
}

int insertRecordInAscendingOrder(Record **head, char *make, int year, int stock)
{
    Record *previous = *head;
    Record *newRecord = createRecord(make, year, stock);
    Record *current = *head;
    int compResult;

    if(*head == NULL)
    {
        *head = newRecord;
        printf("Head is null, list was empty\n");
        printList(*head);
        return 1;
    }
    else if ( compareCars(newRecord, *head)==-1) 
    {
        *head = newRecord;
        (*head)->next = current;
        printf("New record was less than the head, replacing\n");
        printList(*head);
        return 1;
    }
    else
    {
        printf("standard case, searching and inserting\n");
        previous = *head;

        while ( current != NULL &&(compareCars(newRecord, current)==1)) 
        {
            printList(*head);
            previous = current; 
            current = current->next; 
        }

        printList(*head);
        previous->next = newRecord;
        previous->next->next = current;
    }
    return 1;
}

/*creates records from info passed in from main via insertRecordInAscendingOrder.*/
Record* createRecord(char *make, int year, int stock)
{
    printf("CreateRecord\n");
    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;
}

/*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");
}

命令行参数所需的文本文件可以以您喜欢的任何名称保存；以下是您需要的内容:

    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

在此先感谢您的帮助。我将继续亲自努力。

Answer 1

问题是

else if(compStrResult == 1)

您检查 strcmp 的特定返回值。规范仅说明在各种情况下结果是正数、负数或零，而且通常是第一个不同字符之间的差异。你应该检查

if (compStrResult > 0)

那里。