C语言动态数组realloc导致Heap block错误信息

Question

我刚刚开始学习C编程并练习动态数组以及malloc和realloc。我正在使用 Visual Studio，代码位于文件扩展名 .c 中但我不知道为什么 realloc 会导致错误消息“HEAP[Assignment1Start.exe]:01217FA8 处的堆 block 在 01217FE8 处修改，过去请求的大小为 38”请按住 ctrl-f 这句话“Here I Want to realloc”它将引导您到导致错误消息的行。

    #define _CRT_SECURE_NO_DEPRECATE 
    #include<stdio.h>
    #define _CRT_SECURE_NO_WARNINGS

    #define _NO_DEBUG_HEAP 1

    int main()
    {
        FILE *ptr_file;
        FILE *ptr_file2;
        char buf[1000]; //1000 characters array. //if label[10] = "Single"; then label[2] outputs "n"// label[6] outputs "\0" // label[7] outputs " " empty space

        char *vArray2; //is as pointer to a character, to which you allocated memory to hold exactly 1 character.
        int NoOfTasks = 0;
        char **ArrayNo;
        char **ArrayTemp;
        //#define ArrayCapacity 15
        int ArrayCapacity = 20;
        #define ID_LEN 10
        int i;
        int power = 1;
        int quitbtn = 8;


        ptr_file = fopen("output.txt", "r");
        if (!ptr_file)
            return 1;

        ArrayNo = (char*)malloc(ArrayCapacity*sizeof(char)); //allocate some memory that your pointer will point to. //You should always make it point to something or you can allocate some memory that your pointer will point to.

        ArrayNo[NoOfTasks] = malloc((ID_LEN + 1) * sizeof(char));
        strcpy(ArrayNo[NoOfTasks], "Quit\n");
        NoOfTasks += 1;

        while (fgets(buf, 1000, ptr_file) != NULL) //fgets adds the \n to the end of each line it reads and stores it in buf //outputs to command prompt//If the end-of-file (EOF) is reached the fgets function will return a NULL value
        {

            ArrayNo[NoOfTasks] = malloc((ID_LEN + 1) * sizeof(char));
            strcpy(ArrayNo[NoOfTasks], buf);

            NoOfTasks += 1;
        }

        while (power == 1){

            for (int r = 0; r < NoOfTasks; r++){

                    printf("%d %s", r,ArrayNo[r]);

            }

            printf("\n Please enter the task order number");

            int userInputInt1 = 0;

            scanf("%d", &userInputInt1);

            if (userInputInt1 != 0) //0 is quit NoOfTasks-1
            {
                printf("\n %s (1)Add task (2) Remove Task (3)Replace Task", ArrayNo[userInputInt1]);
                int userInputInt2 = 0;
                scanf("%d", &userInputInt2);
                //int result = atoi(userInput2); // convert string to int

                if (userInputInt2 == 3)
                {
                    printf("\n Type in new task");
                    char userInput3[30];
                    scanf("%s", &userInput3);

                    if (userInput3 != " "){

                        int n;

                        printf("\n %s Replaced with %s \n", ArrayNo[userInputInt1], &userInput3);

                        strcpy(ArrayNo[userInputInt1], &userInput3);
                        strcat(ArrayNo[userInputInt1], "\n");
                    }
                }
                if (userInputInt2 == 2) //remove
                {
                    int n;
                    NoOfTasks -= 1;
                    for (int c = userInputInt1; c < NoOfTasks; c++){
                        printf("\n %s Replaced with %s", ArrayNo[userInputInt1], ArrayNo[c + 1]);
                        ArrayNo[c] = ArrayNo[c + 1];
                    }
                }
                if (userInputInt2 == 1) //add
                {
                    printf("\n Add a task");
                    char userInput4[30];
                    scanf("%s", &userInput4);


                    ArrayCapacity += 1;// increase ArrayCapacity by 1 because a new task is added
                    ArrayNo = (char**)realloc(ArrayNo, (ArrayCapacity* sizeof(char*))); // here I want to realloc memory for new element of the array ArrayNo when a new task is added
                    ArrayNo[NoOfTasks] = malloc((ID_LEN + 1) * sizeof(char));
                    strcpy(ArrayNo[NoOfTasks], &userInput4);

                    NoOfTasks += 1;
                }

            }
            if (userInputInt1 == 0) //8 is quit NoOfTasks-1
            {
                ptr_file2 = fopen("WriteTo2.txt", "w");
                if (!ptr_file2)
                    return 1;
                for (int r = 1; r < NoOfTasks; r++){

                    fprintf(ptr_file2, "%s\n", ArrayNo[r]);
                }
                printf("\n You quit the program");
                fclose(ptr_file2);
                fclose(ptr_file);
                power = 0;
            }
        }


        getchar();
        getchar();
        getchar();
        return 0;
    }

Answer 1

初始分配不正确。

ArrayNo 是 char**。你也这么做了

ArrayNo = (char*)malloc(ArrayCapacity*sizeof(char)); 

这仅分配 ArrayCapacity 字节(sizeof(char) 为 1)。数组实际上需要更多，ArrayCapacity*4 或 ArrayCapacity*8 字节(sizeof(char*) 是 4 或 8；比方说如果是 4，那么 ArrayNo[5] 从偏移量 4*5 开始，该偏移量已经超出了分配的区域)。因此，当您填充数组时，您会覆盖一些不允许的内存字节，幸运的是 realloc (在 Debug模式下)对此进行了检查，并在发现后立即停止执行内存损坏。