尝试从堆中释放字节时程序崩溃

Question

在我的程序中，我试图获取一个完整的堆，将其发送到另一个函数，创建一个更大大小的新堆，复制旧堆中的值，释放旧堆并返回新堆以继续使用。然而，当我尝试释放堆时，我遇到了总线错误。据我了解，我将释放这个旧堆，并且新堆应该继续并在此实现中取代旧堆，直到它也需要更新。我尝试更改正在释放的堆，但这没有什么区别。此外，我尝试不使用“grades = arr”行，因为它只复制 arr 的地址，不会做太多事情，但它确实允许我的程序在崩溃之前运行更长时间，所以我选择保留它。任何对此的帮助将不胜感激。对于上下文，grades 是原始堆，最初分配了 40 字节的内存。

void gradeScanner(int gradeCount, int allocCount, double* grades)
{
    int i = 0;
    while (i != 5) {
        scanf("%lf", &myGrade);
        if (myGrade > 0 && i == 4) {
            *(grades + gradeCount) = myGrade;
            gradeCount++;
            allocCount++;
            printf("%s", "stored ");
            printf("%lf", myGrade);
            printf("%s", "in the heap at ");
            printf("%p\n", (void*)(grades + i));
            printf("%s", "heap at ");
            printf("%p", (void*)(grades + i));
            printf("%s\n", "is full");
            expander(grades, gradeCount, allocCount);
            i = 0;
        }
        else if (myGrade > 0) {
            *(grades + gradeCount) = myGrade;
            gradeCount++;
            printf("%s", "stored ");
            printf("%lf", myGrade);
            printf("%s", "in the heap at ");
            printf("%p\n", (void*)(grades + i));
            i++;
        }
        else if (myGrade < 0) {
            i = 5;
            average(grades, gradeCount);
            evaluator(grades, gradeCount);
        }
    }
}

double* expander(double* grades, int gradeCount, int allocCount)
{
    int x = allocCount * 40;
    double* arr = (double*)malloc(x);
    printf("%s", "Allocated ");
    printf("%d", x);
    printf("%s", " bytes to the heap at ");
    printf("%p\n", (void*)arr);
    printf("%s", "copied ");
    for (int i = 0; i < gradeCount; i++) {
        printf("%s", "hiya");
        *(arr + i) = *(grades + i);
    } //for
    oldAlloc = x;
    grades = arr;
    free(grades);
    printf("%d", gradeCount);
    printf("%s", " grades from ");
    printf("%p", (void*)grades);
    printf("%s", " to ");
    printf("%p\n", (void*)arr);
    printf("%s", " Freed ");
    printf("%d", oldAlloc);
    printf("%s", " byes from the heap at ");
    printf("%p\n", (void*)grades);
    return arr;
} //expander

Answer 1

grades = arr;  
free(grades);

出故障了。程序通过将 grades 指向新数组来泄漏旧的 grades 数组，然后释放新数组。

free(grades);
grades = arr;  

将释放旧的grades数组，然后将grades指向新数组。

注：以下内容纯属猜测。

我怀疑 gradeScanner 应该看起来更像这样：

void gradeScanner(int gradeCount, int allocCount, double* grades)
{
    while (true) // keep going until user inputs bad grade 
    {
        if (scanf("%lf", &myGrade) == 1) // got a valid input from user
        {
            if (myGrade >= 0) // got a valid grade
            {
                if (gradeCount == allocCount) // array full. expand it
                {
                    allocCount++; // strongly consider expanding by more than one 
                                  // memory allocation and all the copying is expensive.
                                  // Unless you have memory constraints, it's better 
                                  // to waste a bit of memory in order to do fewer
                                  // reallocations and copies.
                    expander(grades, gradeCount, allocCount);
                }
                *(grades + gradeCount) = myGrade; // store the grade
                gradeCount++;
            }
            else // didn't get a valid grade
            {
                average(grades, gradeCount);
                evaluator(grades, gradeCount);
                return; // done scanning grades
            }
        }
        else // user didn't input a number
        {
            // clean up bad input and request a new one
        }
    }
}