c - realloc 指针指向随机内存，导致程序崩溃

Question

我在第二个函数中的 realloc 语句运行到一个点，然后指针似乎突然指向随机内存。有人可以解释一下我该如何解决这个问题吗？查看输出可能会节省一些时间。谢谢。

int main()
{

    int testCases, i, n;
    int* primeArray;
    int* size;

    primeArray = malloc(sizeof(int));
    primeArray[0] = 2;
    size = 1;

    int number = 2;
    while(number < 1000){
        number = nextPrime(number, primeArray, &size);
        printf("Prime Array at %d is %d, size is %d, number is %d \n", 0, primeArray[0], size, number);
    }


    scanf("%d", &testCases);
    for(i = 0; i < testCases; i++){
        scanf("%d", n);

    }

    free(primeArray);
    free(size);
    return 0;
}

第二个函数:

int nextPrime(int number, int* primeArray, int* size){
    int foundPrime = 0, num = number, i;
    while(!foundPrime){
        num++;
        int allNums = 0;
        //printf("Size: %d \n", *size);
        for(i = 0; i < *size; i++){
            //printf("%d mod %d \n", num, primeArray[i]);
            if(num % primeArray[i] != 0){
                allNums += 0;
            }
            else {
                allNums = 1;
                break;
            }
        }
        if(allNums == 0){
            *size+=1;
            //printf("Size: %d \n", *size);
            foundPrime = 1;
            primeArray = realloc(primeArray, *size * sizeof(int) );
            primeArray[*size-1] = num;
            //printf("%d \n", primeArray[*size-1]);
            return num;
        }
    }
}

输出:

Prime Array at 0 is 2, size is 2, number is 3  
Prime Array at 0 is 2, size is 3, number is 5  
Prime Array at 0 is 2, size is 4, number is 7  
...  
Prime Array at 0 is 2, size is 94, number is 491  
Prime Array at 0 is 2, size is 95, number is 499  
Prime Array at 0 is 2, size is 96, number is 503  
Prime Array at 0 is 16852008, size is 97, number is 509

Answer 1

primeArray，即使它是一个指针，也会按值传递给您的 nextPrime 函数。因此，如果 realloc 更改指针值(它可以而且经常会这样做)，main 不会在 nextPrime 时将该值反射(reflect)回它返回。一个快速的解决方法是更改​​您的 nextPrime 以获取指向指针参数的指针，而不仅仅是数组指针。

这是一个快速修复，我修改了 nextPrime 的函数签名，并在函数的开始和结束处添加了代码。

int nextPrime(int number, int** ptrToPrimeArray, int* size){

    int* primeArray = *ptrToPrimeArray;  // primeArray is the deferenced value of ptrToPrimeArray

    int foundPrime = 0, num = number, i;
    while(!foundPrime){
        num++;
        int allNums = 0;
        //printf("Size: %d \n", *size);
        for(i = 0; i < *size; i++){
            //printf("%d mod %d \n", num, primeArray[i]);
            if(num % primeArray[i] != 0){
                allNums += 0;
            }
            else {
                allNums = 1;
                break;
            }
        }
        if(allNums == 0){
            *size+=1;
            //printf("Size: %d \n", *size);
            foundPrime = 1;
            primeArray = realloc(primeArray, *size * sizeof(int) );
            primeArray[*size-1] = num;
            //printf("%d \n", primeArray[*size-1]);

            *ptrToPrimeArray = primeArray;   // return the changed value of primeArray back to the caller

            return num;
        }
    }
}

然后在 main 中调用它，如下所示:

number = nextPrime(number, &primeArray, &size);