使用malloc為堆疊中的堆疊分配記憶體時，它回傳NULL-有解無憂

我有動態記憶體的問題。我有一個堆疊，其中包含有關陣列長度的資訊，以及指向另一個堆疊的指標。最終目標是制作一個購物清單，其中包含隨著用戶添加商品而不斷擴展的商品串列。它由三個檔案組成。

我對編碼很陌生，所以這個問題可能（希望）很容易解決。

購物清單.h

#ifndef SHOPPING_LIST_H
#define SHOPPING_LIST_H
#define SIZE 100
/*H?r l?gger du eventuella makrodefinitioner*/


// Struct definitions


struct GroceryItem {
    char productName[SIZE];
    float amount;
    char unit[SIZE];
};

struct ShoppingList{
    struct GroceryItem *itemList;
    int length;
};



// Function declarations

void addItem(struct ShoppingList *list);
void printList(struct ShoppingList *list);
void editItem(struct ShoppingList *list);
void removeItem(struct ShoppingList *list);
void saveList(struct ShoppingList *list); //implementeras i laboration 7
void loadList(struct ShoppingList* list); //implementeras i laboration 7

#endif

這是包含在第三個檔案中呼叫不同功能的主函式的檔案。

#define _CRT_SECURE_NO_WARNINGS
#include "ShoppingList.h"
#include <stdio.h>
#define CLEAR while(getchar() != '\n');


int main(void)
{
    struct ShoppingList shoppingList;
    shoppingList.length = 0; // The shopping list is empty at the start
    shoppingList.itemList = NULL;

    int option;

    do
    {
        printf("\n\nWelcome to the shopping list manager!\n");
        printf("=====================================\n\n");

        printf("1. Add an item\n");
        printf("2. Display the shopping list\n");
        printf("3. Remove an item\n");
        printf("4. Change an item\n");
        printf("5. Save list\n"); 
        printf("6. Load list\n"); 
        printf("7. Exit\n");

        printf("What do you want to do? ");
        scanf("%d", &option); CLEAR

        switch (option)
        {
        case 1: addItem(&shoppingList); break;
        case 2: printList(&shoppingList); break;
        case 3: removeItem(&shoppingList); break;
        case 4: editItem(&shoppingList); break;
        case 5: saveList(&shoppingList); break;
        case 6: loadList(&shoppingList); break;
        case 7: break;
        default:
            printf("Please enter a number between 1 and 7");
        }
    } while (option != 7);

    return 0;
}

這是包含有關如何添加專案、洗掉等代碼的所有函式的檔案。最后一個包含 malloc 和 realloc 動態記憶體分配的函式不起作用，我不知道是什么原因造成的。

#define _CRT_SECURE_NO_WARNINGS
#include"ShoppingList.h"
#include<stdio.h>
#include<stdlib.h> // For dynamic memory (lab 7)
#include <string.h>
#define CLEAR while(getchar() != '\n'); 


void enterProductName(struct ShoppingList* plist);
void enterUnit(struct ShoppingList* plist);
void negativeCheck(struct ShoppingList* plist);
void editItem(struct ShoppingList* list);
void editItemMenu(struct ShoppingList* list);
void itemDeleter(struct ShoppingList* list, int deleteThis);
int memoryAllocator(struct ShoppingList** ListInMemory, int length);
void memoryReturn(struct ShoppingList* list);


void addItem(struct ShoppingList* list)
{
    int error = 0;
        
    error = memoryAllocator(list->itemList, list->length);
    if (error == 0)
        return;

    enterProductName(list);

    negativeCheck(list);

    enterUnit(list);
    
    printf("This item has been added!\n\n");
    list->length = list->length   1;
    return;
}

void printList(struct ShoppingList *list)
{

    if (list->length == 0) {
        printf("\nYour shoppinglist is empty! Start by adding an item.");
        return;
    }

    printf("\nYour shopping list\n\n");
    printf("Nr Item\t\t       Ammount\tUnit\n");
    for (int i = 0; i < 5 && i < list->length; i  ) {
        printf("%d. %-20s", i 1, list->itemList[i].productName);
        printf("%-8.1f %s\n", list->itemList[i].amount, list->itemList[i].unit);
    }
}

void editItem(struct ShoppingList *list)
{
    printf("\nYour shopping list\n\n");
    printf("Nr Item\t\t       Ammount\tUnit\n");
    for (int i = 0; i < 5 && i < list->length; i  ) {
        printf("%d. %-20s", i   1, list->itemList[i].productName);
        printf("%-8.1f %s\n", list->itemList[i].amount, list->itemList[i].unit);
    }

    editItemMenu(list);
}

void removeItem(struct ShoppingList *list)
{
    int itemToDelete = 0, itemDeleteConfirm = 0;
    
    if (list->length == 0) {
        printf("Your shopping list is empty.");
    }
    else {
        printf("\nYour shopping list\n\n");
        printf("Nr Item\t\t       Ammount\tUnit\n");
        for (int i = 0; i < 5 && i < list->length; i  ) {
            printf("%d. %-20s", i   1, list->itemList[i].productName);
            printf("%-8.1f %s\n", list->itemList[i].amount, list->itemList[i].unit);
        }

        printf("\nEnter the number of the item you with to delete: ");
        scanf("%d", &itemToDelete); CLEAR

            printf("Are you sure you want to delete this item? 0 - no, 1 - yes: ");
        scanf("%d", &itemDeleteConfirm);

        if (itemDeleteConfirm == 1)
        {
            itemDeleter(list, itemToDelete);
        }
    }
}

/*saveList och loadList implementeras i laboration 7*/
void saveList(struct ShoppingList *list)
{
    free(list->itemList);
}

void loadList(struct ShoppingList* list)
{
    
}

void enterProductName(struct ShoppingList* plist) {
    printf("Enter item name: ");
    fgets(plist->itemList[plist->length].productName, SIZE, stdin);
    plist->itemList[plist->length].productName[strlen(plist->itemList[plist->length].productName) - 1] = '\0';
}

void enterUnit(struct ShoppingList* plist) {
    printf("Enter the unit (e.g. kg): ");
    fgets(plist->itemList[plist->length].unit, SIZE, stdin);
    plist->itemList[plist->length].unit[strlen(plist->itemList[plist->length].unit) - 1] = '\0';
}

void negativeCheck(struct ShoppingList* plist) {
    int ammountNegative = 1;
    do {
        printf("Enter ammount: ");
        scanf("%f", &plist->itemList[plist->length].amount); CLEAR

            if (plist->itemList[plist->length].amount < 0) {
                printf("\nYou can only enter positive numbers!\n");
                ammountNegative = 1;
            }
            else
                ammountNegative = 0;
    } while (ammountNegative != 0);
}

void editItemMenu(struct ShoppingList *list) {

    int editItemWhat = 0;
    int editItemNumber = 0;
    printf("\nWhat item would you like to edit?");
    printf("\nEnter the items number to edit it: ");
    scanf("%d", &editItemNumber); CLEAR

    printf("What would you like to edit?\n");
    printf("1. Name\n");
    printf("2. Ammount\n");
    printf("3. Unit\n");
    printf("\nEnter number to edit: ");
    scanf("%d", &editItemWhat); CLEAR

        editItemNumber--;

    switch (editItemWhat)
    {
    case 1:printf("Enter new name: "); fgets(list->itemList[editItemNumber].productName, SIZE, stdin);
           list->itemList[editItemNumber].productName[strlen(list->itemList[editItemNumber].productName) - 1] = '\0'; break;
    case 2:printf("Enter new ammount: "); scanf("%f", &list->itemList[editItemNumber].amount); break;
    case 3:printf("Enter new unit: "); fgets(list->itemList[editItemNumber].unit, SIZE, stdin);
           list->itemList[editItemNumber].unit[strlen(list->itemList[editItemNumber].unit) - 1] = '\0'; break;
    default: break;
    }
}

void itemDeleter(struct ShoppingList* list, int deleteThis) {
    
    for (int i = deleteThis - 1; i < list->length; i  ) {
        list->itemList[i] = list->itemList[i   1];
    }
    list->length = list->length - 1;
}


int memoryAllocator(struct ShoppingList** ListInMemory, int length){
    struct ShoppingList* temp;

    if (length == 0) {
        temp = (struct ShoppingList*)calloc(1, sizeof(struct ShoppingList));
    }
    else {
        temp = (struct ShoppingList*)realloc(*ListInMemory, (length   1) * sizeof(struct ShoppingList));
    }
    if (temp != NULL) {
        printf("A memory error has occured, please try again\n");
        return 0;
    }
    else {
        *ListInMemory = temp;
        return 1;
    }
}

void memoryReturn(struct ShoppingList* list) {
    free(list->itemList);
}

無論我做什么或嘗試什么，我都無法讓 malloc 函式回傳任何其他在 if 函式中被拒絕的 NULL 。如果沒有 if 函式，它會給出錯誤，指標是 nullptr 并崩潰。

uj5u.com熱心網友回復：

大部分更改都在memoryAllocator
更改了對memoryAllocatorin addItem
memoryAllocatorallocates的呼叫，GroceryItem而不是ShoppingList
其他功能被洗掉以待稍后實作。

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

#define SIZE 100
#define CLEAR while(getchar() != '\n');

struct GroceryItem {
    char productName[SIZE];
    float amount;
    char unit[SIZE];
};

struct ShoppingList{
    struct GroceryItem *itemList;
    int length;
};

void enterProductName(struct ShoppingList* plist);
void enterUnit(struct ShoppingList* plist);
void negativeCheck(struct ShoppingList* plist);
int memoryAllocator(struct ShoppingList* ListInMemory, int length);
void memoryReturn(struct ShoppingList* list);

void addItem(struct ShoppingList* list) {
    int error = 0;

    error = memoryAllocator(list, list->length);
    if (error == 0)
        return;

    enterProductName(list);

    negativeCheck(list);

    enterUnit(list);

    printf("This item has been added!\n\n");
    return;
}

void printList(struct ShoppingList *list) {
    if (list->length == 0) {
        printf("\nYour shoppinglist is empty! Start by adding an item.");
        return;
    }

    printf("\nYour shopping list\n\n");
    printf("Nr Item\t\t       Ammount\tUnit\n");
    for (int i = 0; i < list->length; i  ) {
        printf("%d. %-20s", i 1, list->itemList[i].productName);
        printf("%-8.1f %s\n", list->itemList[i].amount, list->itemList[i].unit);
    }
}

void enterProductName(struct ShoppingList* plist) {
    int item = plist->length - 1;
    printf("Enter item name: ");
    fgets(plist->itemList[item].productName, SIZE, stdin);
    plist->itemList[item].productName[strlen(plist->itemList[item].productName) - 1] = '\0';
}

void enterUnit(struct ShoppingList* plist) {
    int item = plist->length - 1;
    printf("Enter the unit (e.g. kg): ");
    fgets(plist->itemList[item].unit, SIZE, stdin);
    plist->itemList[item].unit[strlen(plist->itemList[item].unit) - 1] = '\0';
}

void negativeCheck(struct ShoppingList* plist) {
    int item = plist->length - 1;
    int ammountNegative = 1;
    do {
        printf("Enter ammount: ");
        scanf("%f", &plist->itemList[item].amount); CLEAR

            if (plist->itemList[item].amount < 0) {
                printf("\nYou can only enter positive numbers!\n");
                ammountNegative = 1;
            }
            else
                ammountNegative = 0;
    } while (ammountNegative != 0);
}

int memoryAllocator(struct ShoppingList* ListInMemory, int length){
    struct GroceryItem* temp;

    temp = realloc(ListInMemory->itemList, (length   1) * sizeof *temp);
    if (temp == NULL) {
        printf("A memory error has occured, please try again\n");
        return 0;
    }
    else {
        temp[length].productName[0] = 0;
        temp[length].amount = 0.0f;
        temp[length].unit[0] = 0;
        ListInMemory->itemList = temp;
        ListInMemory->length  = 1;
        return 1;
    }
}

void memoryReturn(struct ShoppingList* list) {
    free(list->itemList);
}

int main(void)
{
    struct ShoppingList shoppingList;
    shoppingList.length = 0; // The shopping list is empty at the start
    shoppingList.itemList = NULL;

    int option;

    do
    {
        printf("\n\nWelcome to the shopping list manager!\n");
        printf("=====================================\n\n");

        printf("1. Add an item\n");
        printf("2. Display the shopping list\n");
        printf("3. Remove an item\n");
        printf("4. Change an item\n");
        printf("5. Save list\n");
        printf("6. Load list\n");
        printf("7. Exit\n");

        printf("What do you want to do? ");
        scanf("%d", &option); CLEAR

        switch (option)
        {
        case 1: addItem(&shoppingList); break;
        case 2: printList(&shoppingList); break;
        case 3: break;
        case 4: break;
        case 5: break;
        case 6: break;
        case 7: memoryReturn(&shoppingList); break;
        default:
            printf("Please enter a number between 1 and 7");
        }
    } while (option != 7);

    return 0;
}

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