c - 数组的段错误

Question

我遇到段错误问题。当我在带有 devc++ 或代码块的 Windows 机器上运行此特定代码时，它会按照我的预期运行。当我尝试在 linux 机器上运行时出现问题。有人告诉我，这很可能是由于指针试图访问不允许访问的位置，但我不明白为什么。

当我在没有“empinfo.txt”文件的情况下运行程序时，它将启动并允许我执行除“1-Add”之外的任何菜单选项，所以问题似乎与我的方式有关我在我的结构中使用数组。

我包含了所有代码，但唯一的问题函数(我认为)是初始化和添加。非常感谢任何有关在这种情况下使用字符数组的正确方法的帮助。

这是 empinfo.txt 文件中的示例输入

12   JackSprat   2     1    65000
13   HumptyDumpty  5   3    30000
17   BoPeep  2       3      30000
20   BoyBlue    3    2      58000
0

-

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

FILE *empinfo=NULL;

struct employeeData {
    int EMP_ID;
    char name[20];
    int dept;
    int rank;
    double salary;
    struct employeeData *next;
};

struct employeeData *head = NULL;

void initializeList();
void add(int ID, char name[0], int dept, int rank, double newSalary);
void deleteEmp(int ID);
void modify(int ID, double NewSalary);
void query(int rank);
void print();

int main(){

    int choice=1, ID=0, rank=0, dept=0;
    double newSalary=0;
    char name[20];
    initializeList();

    while (choice != 0) {
        printf("1-Add 2-Delete 3-Modify 4-Query 5-Print 0-Exit\n");
        fflush(stdin);
        scanf("%d", &choice);

        if (choice == 1) {
            printf("Enter new employee info. Format: \"ID name dept rank salary\"\n");
            if((scanf("%d %s %d %d %lf", &ID, name, &dept, &rank, &newSalary))==5)
                add(ID, name, dept, rank, newSalary);
            else{
                printf("invalid format entered\n\n");
                continue;
            }
        }
        else if (choice == 2){
            printf("Enter employee ID to delete: ");
            if(scanf("%d", &ID)==1){
                deleteEmp(ID);}
            else{
                printf("Employee ID must be an integer\n");
                continue;
            }
        }
        else if (choice == 3){
            printf("Enter employee ID to modify: ");
            if(scanf("%d", &ID)==1){
                printf("Enter new salary amount: ");
                if(scanf("%lf", &newSalary)==1)
                    modify(ID,newSalary);
                else
                    printf("Salary must be a number\n");
            }
            else{
                printf("Employee ID must be an integer\n");
                continue;
            }
        }
        else if (choice == 4){
            printf("Enter the rank you wish to query: ");
            scanf("%d", &rank);
            query(rank);
        }
        else if (choice == 5){
            print();
        }
    }
    printf("Goodbye...\n");
    head=NULL;
    free(head);
    return 0;
}

void initializeList(){


    empinfo=fopen("empinfo.txt", "r");
    head = (struct employeeData *)malloc(sizeof(struct employeeData));
    head->next = NULL;
    if (empinfo==NULL){
        printf("empinfo.txt not found, file not opened.\n");
        head=NULL;
        free(head);
        free(empinfo);
        return;
    }

    struct employeeData *tempPtr = head;


    while (tempPtr->EMP_ID != 0){
        fscanf(empinfo, "%d %s %d %d %lf", &tempPtr->EMP_ID, tempPtr->name, &tempPtr->dept, &tempPtr->rank, &tempPtr->salary);
        if (tempPtr->EMP_ID == 0){
            break;
            }
        tempPtr->next = (struct employeeData *)malloc(sizeof(struct employeeData));
        tempPtr=tempPtr->next;
    }
    tempPtr=head;
    while(tempPtr->next->EMP_ID!=0){
        tempPtr=tempPtr->next;
    }
    empinfo=NULL;
    free(empinfo);
    tempPtr->next=NULL;
    fclose(empinfo);
    tempPtr=NULL;
    free(tempPtr);
}

void add(int ID, char name[], int dept, int rank, double newSalary){
    struct employeeData *tempPtr = head;
    while ((tempPtr->next!=NULL) && (tempPtr->next->EMP_ID < ID)) {
        tempPtr=tempPtr->next;
    }
    struct employeeData *newNode = (struct employeeData * )malloc(sizeof(struct employeeData));
    newNode->EMP_ID = ID;
    strcpy(newNode->name,name);
    newNode->dept = dept;
    newNode->rank = rank;
    newNode->salary = newSalary;
    newNode->next=NULL;
    if (tempPtr==head) {
        if(ID>tempPtr->EMP_ID){
            newNode->next = tempPtr->next;
            tempPtr->next = newNode;
        }
        else {
            newNode->next=tempPtr;
            head=newNode;
        }
    }
    else if (tempPtr->next == NULL){
        tempPtr->next=newNode;
        newNode->next=NULL;
    }
    else{
        newNode->next = tempPtr->next;
        tempPtr->next = newNode;
    }
    printf("Employee #%d has been added to the database.\n\n", ID);
    tempPtr=NULL;
    newNode=NULL;
    free(newNode);
    free(tempPtr);

}
void deleteEmp(int ID){
    struct employeeData *seek=head,*tempPtr = head;

    if(head!=NULL) {
        while((tempPtr->EMP_ID!=ID)){
                seek = tempPtr;
                tempPtr=tempPtr->next;
                if(tempPtr==NULL){
                    printf("Employee ID not found\n");
                    free(tempPtr);
                    seek=NULL;
                    free(seek);
                    return;
                }
        }
        if (tempPtr!=NULL){
            if(tempPtr==head){
                if(tempPtr->next==NULL){
                    printf("List cannot be empty\n");
                    free(tempPtr);
                    seek=NULL;
                    free(seek);
                    return;
                }
                head=tempPtr->next;
                free(tempPtr);
            }
            else if (tempPtr->next==NULL){
                free(tempPtr);
                seek->next = NULL;
            }
            else{
                seek->next=tempPtr->next;
                free(tempPtr);
            }
        }
    }
    printf("Employee #%d has been deleted\n", ID);
    tempPtr=NULL;
    free(tempPtr);
    seek=NULL;
    free(seek);
}

void modify(int ID, double NewSalary){
    struct employeeData *tempPtr = head;

    while (tempPtr!=NULL&&tempPtr->EMP_ID!=ID){
        tempPtr=tempPtr->next;
    }
    if(tempPtr==NULL){
        printf("Employee ID not found\n");
        free(tempPtr);
        return;
    }
    tempPtr->salary=NewSalary;
    printf("Employee salary updated.\n\n");
    tempPtr=NULL;
    free(tempPtr);
}

void query(int rank){
    struct employeeData *tempPtr = head;

     while (tempPtr!=NULL){
        if(tempPtr->rank == rank){
            printf("%s\n", tempPtr->name);
            tempPtr=tempPtr->next;
        }
        else
            tempPtr=tempPtr->next;
     }
     tempPtr=NULL;
     free(tempPtr);
}

void print(){
    struct employeeData *tempPtr = head;

    while (tempPtr!=NULL){
        printf("%d %s %d %d %.0lf\n", tempPtr->EMP_ID, tempPtr->name, tempPtr->dept, tempPtr->rank, tempPtr->salary);
        tempPtr=tempPtr->next;
    }
    free(tempPtr);

Answer 1

使用调试器。如果你在 Linux 上，你可能可以访问 gdb。这是您的示例和提供的测试文件的 session :

$ gdb test
...
(gdb) run
...
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400bb2 in initializeList () at test.c:111
111     while(tempPtr->next->EMP_ID!=0){
Missing separate debuginfos, use: debuginfo-install glibc-2.18-14.fc20.x86_64
(gdb) p tempPtr
$1 = (struct employeeData *) 0x603250
(gdb) p tempPtr->next
$2 = (struct employeeData *) 0x0

在第111行我们可以看到我们正在尝试解引用一个NULL指针，根据这些信息应该很容易定位问题。

这也肯定会导致错误:

empinfo=fopen(...)
...
empinfo=NULL;
free(empinfo);
fclose(empinfo);

您不应该释放从 fopen 获得的句柄，也不应该将它设置为 NULL，让 fclose 处理它。