c - 正在使用通用链表/变量而未初始化

Question

所以我正在尝试为赋值编写一个通用程序，但该程序一直告诉我正在使用列表变量而未初始化。我已经尝试了几乎所有我能做的事情，但仍然没有什么不同，所以如果有人能告诉我我做错了什么，我将非常感激。

代码有点长，请多多包涵。

标题内容:

#ifndef _HEADER_H
#define _HEADER_H

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

typedef enum { FALSE, TRUE } BOOL;

/* defining specific function names*/
typedef int(*compare_func)(void*, void*);
typedef void(*print_func)(void*);
typedef void(*free_func)(void*);

/* defining struct names and pointers*/
typedef struct set Set;
typedef struct set* PSet;
typedef struct list List;
typedef struct list* PList;

/* creating and initialzing a set*/
PList createSet(PList List, compare_func cmp_fnc, print_func prnt_fnc, free_func free_fnc);

/* finding the biggest value in the set*/
void* findMax(PList List);

/* finding the smallest value in the set*/
void* findMin(PList List);

/* finding an element in the set*/
BOOL findInSet(PList List, void* val);

/* function for finding the size of the list*/
int setSize(PList list);

/* inserting a new element.*/
BOOL addToSet(PList List, void *data);

/* deleting an element, pointered by todel*/
BOOL deleteFromSet(PList list, void *todel);

/* print the elements in the set */
void printAll(PList list);

/* deleting the entire set */
void deleteSet(PList list);

#endif

执行文件:

    #include "Header.h"

typedef struct set      // Set struct for bi-directional list
{
    void* data;
    struct  set *next, *prev;
}Set, *PSet;

typedef struct list      // List struct
{
    int ListSize;
    Set *head;
    Set *tail;
    compare_func compare;
    print_func print;
    free_func free;
}List, *PList;


PList createSet(PList LIST, compare_func cmp_fnc, print_func prnt_fnc, free_func free_fnc)    // Function for initializing and creating a set
{
    PList list;
    list = (PList)malloc(sizeof(List));
    LIST->ListSize = 0;
    LIST->head = NULL;
    LIST->tail = NULL;
    LIST->compare = cmp_fnc;
    LIST->print = prnt_fnc;
    LIST->free = free_fnc;
    return list;
}


void* findMax(PList List)         // Function for finding the biggest value in a set
{
    if (List->head == NULL)     // If the set is empty
        return NULL;

    PSet temp;
    void* max = List->head->data;
    temp = List->head;
    while (temp)
    {
        if (List->compare(temp->data, max) == 1)      // Finding the biggest value
            max = temp->data;
        temp = temp->next;    // Moving to the next node
    }
    return max;
}


void* findMin(PList List)         // Function for finding the smallest value in a set
{
    if (List->head == NULL)        // If the set is empty
        return NULL;

    PSet temp;
    void* min = List->head->data;
    temp = List->head;
    while (temp)
    {
        if (List->compare(temp->data, min) == -1)       // Finding the smallest value
            min = temp->data;
        temp = temp->next;       // Moving to the next node
    }
    return min;
}


BOOL findInSet(PList List, void* val)        // Function for checking whether a given character is in the set
{
    if (List->head == NULL)    // If the list is empty
        return FALSE;

    PSet temp;
    temp = List->head;
    while (temp)
    {
        if (List->compare(temp->data, val) == 0)        // If the character exists
            return TRUE;
        temp = temp->next;     // Moving to the next node
    }
    return FALSE;
}


int setSize(PList list)
{
    return list->ListSize;
}


BOOL addToSet(PList List, void *data)       // Function for adding an item to the set
{
    PSet temp, CurrentNode;
    CurrentNode = List->head;
    temp = (PSet)malloc(sizeof(Set));
    if (temp == NULL)           // If the allocation failed return false
        return FALSE;

    temp->data = data;       // Filling the temp with the data
    temp->next = NULL;
    temp->prev = NULL;

    if (List->head == NULL)      // If the list is empty
    {
        List->head = temp;
        List->tail = temp;
        List->ListSize++;
        return TRUE;
    }
    else {
        while (CurrentNode)          // Loop for checking whether the inserted character exists in the list
        {
            if (List->compare(data, CurrentNode->data) == 0) return FALSE;
            CurrentNode = CurrentNode->next;
        }
        List->tail->next = temp;   // Adding the node to the list
        temp->prev = List->tail;
        List->tail = temp;     // Updating the tail
        List->ListSize++;
        return TRUE;
    }
}


BOOL deleteFromSet(PList list, void *todel)         // Function for deleteing an item from a set
{
    PSet nodeToDel;

    if (list->head == NULL)      // If the list is empty
        return FALSE;

    if (list->compare(todel, list->head->data) == 0)    // If the node to be deleted is the head
    {
        nodeToDel = list->head;
        list->head = list->head->next;
        if (list->head != NULL)
            list->head->prev = NULL;
        list->free(nodeToDel->data);
        free(nodeToDel);
        list->ListSize--;
        return TRUE;
    }
    else if (list->compare(todel, list->tail->data) == 0)         // If the node to be deleted is the tail
    {
        nodeToDel = list->tail;
        list->tail = list->tail->prev;
        list->tail->next = NULL;
        list->free(nodeToDel->data);
        free(nodeToDel);
        list->ListSize--;
        return TRUE;
    }
    else
    {
        nodeToDel = list->head;
        while (nodeToDel->next)      // Any node other than the head or the tail
        {
            if (list->compare(todel, nodeToDel->data) == 0)     // If the character exists in the list
            {
                nodeToDel->next->prev = nodeToDel->prev;
                nodeToDel->prev->next = nodeToDel->next;
                list->free(nodeToDel->data);
                free(nodeToDel);
                list->ListSize--;
                return TRUE;
            }
            nodeToDel = nodeToDel->next;       // Moving to the next node
        }
    }
    return FALSE;      // If the character wasn't found in the list return false
}


void printAll(PList list)        // Funciton for printing all items in a set
{
    PSet temp;
    if (list->head == NULL)      // If the list is empty
        printf("\nThe list is empty.");
    else
    {
        printf("\nThe list is:\n");
        temp = list->head;
        while (temp)       // While there are still nodes left
        {
            list->print(temp->data);   // Call specific function for printing
            temp = temp->next;     // Move to the next node
        }
        printf("\n");
    }
}


void deleteSet(PList list)       // Function for deleting a set
{
    PSet temp;
    if (!(list->head))   // If the list is empty
        printf("\nThe set is empty.");
    else
    {
        while (list->head)
        {
            temp = (list->head);
            list->head = list->head->next;   // Moving to the next node
            if (list->head != NULL)
                list->head->prev = NULL;
            list->free(temp->data);     // Call specific function for freeing memory
            free(temp);
            list->ListSize--;
        }
        printf("The set has been deleted.\n");
    }
}

主要功能:

#include "Header.h"

void prnt_string(void* str)       // specific function for printing strings
{
    puts(*(char*)str);
    printf(" ");
}

void free_string(void* str)     // specific function for freeing memory
{
    free(str);
}

int cmp_str(void* s1, void* s2)     // specific function for comparing two strings
{
    if (strcmp(*(char*)s1, *(char*)s2) == 0)
        return 0;
    else if (strcmp(*(char*)s1, *(char*)s2 == 1))
        return 1;
    else return -1;
}


void prnt_int(void* a)     // Specific function for printing integers
{
    printf("%d ", a);
}

void free_int(void* a)      // Specific funtion for freeing integers
{
    free(a);
}

int int_comp(void* a, void* b)         // Specific function for printing integers
{
    if (*(int*)a == *(int*)b)
        return 0;
    else if (*(int*)a > *(int*)b)
        return 1;
    else return -1;
}


int main()
{
    char ch, tempstr[31], *str;
    int n, option, *num, item;
    void *temp;
    BOOL status;
    PList list;

    printf("Choose the type you want to work with:\n");
    printf("1. Integers\n");
    printf("2. Strings\n");
    printf("Enter input: ");
    scanf("%d", &n);

    switch (n)
    {
    case 1:
        list = createSet(list, int_comp, prnt_int, free_int);
        do
        {
            printf("Choose the desired action: ('-1' to exit)\n");
            printf("1. Create a Set\n");
            printf("2. Add To Set\n");
            printf("3. Delete From Set\n");
            printf("4. Find an Item in The Set\n");
            printf("5. Find The Biggest Value In The Set\n");
            printf("6. Find The Smallest Value In The Set\n");
            printf("7. Delete The Set\n");
            printf("Enter input: ");
            scanf("%d", &option);

            switch (option)
            {
            case 1:
                list = createSet(list, int_comp, prnt_int, free_int);
                printf("The Set Has Been Initialized.\n");
                break;
            case 2:
                num = (int*)malloc(sizeof(int));
                if (num == NULL)
                {
                    printf("Memory allocation failed!");
                    deleteSet(list);
                    return 1;
                }
                else
                {
                    printf("Enter a number: ");
                    scanf("%d", &num);
                    status = addToSet(list, num);
                    if (status == TRUE)
                    {
                        printf("Number successfully added to set.\n");
                        printAll(list);
                    }
                    else
                    {
                        printf("Operation failed!\nThe number already exists in the set or memory allocation failed.\n");
                        deleteSet(list);
                        return 1;
                    }
                }
                break;
            case 3:
                printf("Enter number: ");
                scanf("%d", &item);
                status = deleteFromSet(list, &item);
                if (status == TRUE)
                {
                    printf("Number successfully deleted.\n");
                    printAll(list);
                }
                else
                {
                    printf("Operation failed!\nThe number does not exist in the set.");
                    printAll(list);
                }
                break;
            case 4:
                printf("Enter number: ");
                scanf("%d", &item);
                if (findInSet(list, &item) == TRUE)
                    printf("Item exists in the set.\n");
                else if (findInSet(list, &item) == FALSE) printf("Item does not exist in the set.\n");
                /*else if (findInSet(list, &item) == NULL) printf("The set is empty.\n");*/
                break;
            case 5:
                printf("The size of the set is %d", setSize(list));
                break;
            case 6:
                temp = findMax(list);
                if (temp == NULL) printf("The set is empty.\n");
                else printf("The biggest value in the set is %d", (int*)temp);
                break;
            case 7:
                temp = findMin(list);
                if (temp == NULL) printf("The set is empty.\n");
                else printf("The smallest value in the set is %d", (int*)temp);
                break;
            case 8:
                deleteSet(list);
                break;
            }
        } while (option != -1);
        deleteSet(list);
        break;
    case 2:
        list = createSet(list, cmp_str, prnt_string, free_string);
        do
        {
            printf("Choose the desired action: ('-1' to exit)\n");
            printf("1. Create a Set\n");
            printf("2. Add To Set\n");
            printf("3. Delete From Set\n");
            printf("4. Find an Item in The Set\n");
            printf("5. Find The Biggest Value In The Set\n");
            printf("6. Find The Smallest Value In The Set\n");
            printf("7. Delete The Set\n");
            printf("Enter input: ");
            scanf("%d", &option);

            switch (option)
            {
            case 1:
                list = createSet(list, cmp_str, prnt_string, free_string);
                printf("The Set Has Been Initialized.\n");
                break;
            case 2:
                    printf("Enter a string(max of 30 characters): ");
                    gets(tempstr);
                    str = (char*)malloc(strlen(tempstr) + 1 * sizeof(char));
                    if (str == NULL)
                    {
                        printf("Memory allocation failed!\n");
                        deleteSet(list);
                        return 1;
                    }
                    strcpy(str, tempstr);
                    status = addToSet(list, str);
                    if (status == TRUE)
                    {
                        printf("String successfully added to set.\n");
                        printAll(list);
                    }
                    else
                    {
                        printf("Operation failed!\nThe string already exists in the set or memory allocation failed.\n");
                        deleteSet(list);
                        return 1;
                    }
                break;
            case 3:
                printf("Enter string(max of 30 characters): ");
                gets(tempstr);
                status = deleteFromSet(list, &tempstr);
                if (status == TRUE)
                {
                    printf("String successfully deleted.\n");
                    printAll(list);
                }
                else
                {
                    printf("Operation failed!\nThe string does not exist in the set.");
                    printAll(list);
                }
                break;
            case 4:
                printf("Enter string: ");
                gets(tempstr);
                if (findInSet(list, &tempstr) == TRUE)
                    printf("Item exists in the set.\n");
                else if (findInSet(list, &tempstr) == FALSE) printf("Item does not exist in the set.\n");
                /*else if (findInSet(list, &tempstr) == NULL) printf("The set is empty.\n");*/
                break;
            case 5:
                printf("The size of the set is %d", setSize(list));
                break;
            case 6:
                temp = findMax(list);
                if (temp == NULL) printf("The set is empty.\n");
                else
                {
                    printf("The biggest value in the set is ");
                    puts((char*)temp);
                }
                break;
            case 7:
                temp = findMin(list);
                if (temp == NULL) printf("The set is empty.\n");
                else
                {
                    printf("The smallest value in the set is ");
                    puts((char*)temp);
                }
                break;
            case 8:
                deleteSet(list);
                break;
            }
        } while (option != -1);
        deleteSet(list);
        break;
    default:
        printf("Wrong input!\n");
        break;
    }

    getch();
    return 0;
}

当我尝试运行该程序时，我收到错误消息，指出 main 函数中的列表变量在未初始化的情况下被使用，但我不明白为什么它首先需要初始化。可能是什么问题？

Answer 1

每个变量在被读取之前都应该被初始化，否则你从它读取的任何东西都是垃圾。在 C 中，变量不会像在某些其他语言中那样默认初始化。

在您的 createSet() 函数中，您取消了对变量 LIST 的引用，但是 main 中的 list 只是声明为一个指针，而没有将其初始化为实际上指向某物。

您应该在 main 中使用 List 来声明 List list 而不是 PList list。然后将 &list 传递给采用 PList 参数的函数。

此外，您当前的 createSet() 函数将两种初始化对象的方法混合在一起。

你可以传递一个PList给它，然后初始化PList指向的List，所以:

List fooList;
PList pFooList = &fooList;
createSet(pFooList, ...):

然后在 createSet() 中不要使用 malloc 分配新对象。

但您也可以在 createList() 中创建对象，但不要将任何 PList 传递给它。

第一个选项的优点是，如果你想动态分配对象，你可以这样做:

PList pFooList = malloc(sizeof(List));
createSet(pFooList, ...);

但您不必这样做，因为您仍然可以在堆栈上分配对象。

注意事项

正如@MichaelBeer 评论的那样，声明为 static 的变量实际上会自动初始化，但这并不能解决提问者的问题，因为如果 list 是用 static PList list，那么 list 将指向 NULL 而不仅仅是垃圾。