c - realloc 函数不会在 c 中保存具有新值的新元素

Question

函数获取成绩数组，如果元素少于之前，则更改成绩数量，函数将删除这些元素例如:之前:我在另一个函数中输入了3个成绩:100、90、80。之后:在这个函数中，它要求我输入新的金额，我输入了，然后输入了它的等级，70。当我将它返回到主函数并将数组、成绩发送到打印数组的函数后，它保留 3 个元素:100、90、80。请帮助我，我尝试了很多时间但没有成功。

void changeNumOfGrades(int* grades, int size)
{
    int numOfGrades = 0;
    int i = 0;
    do
    {
        if (i > ONE_ITERATION)
        {
            printf("Please enter positive number...\n");
        }
        printf("How many elements would you like? ");
        scanf("%d", &numOfGrades);
        i += 1;
    } while (numOfGrades < 0);
    grades = realloc(grades, numOfGrades*sizeof(int));
    if (!grades)
    {
        printf("Unsuccessful realloc");
        //There is no need to release memory because the realloc is for the same pointer.
    }
    if (numOfGrades > size)
    {
        printf("You have more grades than before,\nPlease enter their grades: \n");
        int newGrade = 0;
        //int newNumOfGrades = numOfGrades - size;
        int i = 0;
        for (i = size + 1; i <= numOfGrades; i++)
        {
            printf("Enter grade number %d: ", i);
            scanf("%d", &newGrade);
            *(grades + i - 1) = newGrade;
            printf("hey %d", *(grades + 1));
        }
    }

}

Answer 1

为了重新分配成绩，您需要以 **grades 形式传递。出于测试原因，我更改了 size 来获取新的分配大小，因此您可以在changeNumOfGrades 之后打印数组

void changeNumOfGrades(int** grades, int *size/*get new size*/)
{
    int numOfGrades = 0;
    int i = 0;
    do
    {
        if (i > ONE_ITERATION)
        {
            printf("Please enter positive number...\n");
        }
        printf("How many elements would you like? ");
        scanf("%d", &numOfGrades);
        i ++;
    } while (numOfGrades < 0);
    printf("%d",numOfGrades);
    *grades =  realloc(*grades, numOfGrades*sizeof(int));/*realloc **grade */
    if (!grades)
    {
        printf("Unsuccessful realloc");
        //There is no need to release memory because the realloc is for the same pointer.
    }
    printf("...\n");
    if (numOfGrades > *size)
    {
        printf("You have more grades than before,\nPlease enter their grades: \n");
        int newGrade = 0;
        //int newNumOfGrades = numOfGrades - size;
        int i = 0;
        for (i = *size + 1; i <= numOfGrades; i++)
        {
            printf("Enter grade number %d: ", i);
            scanf("%d", &newGrade);
            *(*grades + i - 1) = newGrade;
            //printf("hey %d", *(grades + 1));
        }
    }
    *size = numOfGrades;/*get new size allocated*/

}

void main()
{
    int numOfInts;
    int *grades ;
    grades =  malloc(3*sizeof(int));
    memset(grades,0,sizeof(int)*3);
    grades[0]=100;
    grades[1]=80;
    grades[2]=20;
    numOfInts = 3;/*initialize 3 items*/
    changeNumOfGrades(&grades,&numOfInts);
    printf("\n\n");
    for (int i=0;i<numOfInts;i++)
    {
        printf("%d\n",grades[i]);
    }
    free(grades);
}