Question

我在第二个函数中的realloc语句一直工作到一个点，然后指针似乎突然指向随机内存。有人可以解释我如何解决这个问题吗？看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;
}

第二功能：

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

您正在将realloc()返回的值分配给局部变量，当函数nextPrime()返回时，该变量当然会消失。 primeArray中main()的值永远不会改变。

Answer 2

primeArray，即使它是一个指针，也会通过值传递给nextPrime函数。因此，如果realloc更改指针值（因为它可以并且经常会这样），main在nextPrime返回时不会将该值反射回它。快速解决方法是更改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，并在函数的开头和结尾添加了代码。

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);

Realloc指针指向随机内存，崩溃程序

2 个答案: