Segmentation fault (core dumped) - 部分指针被覆盖，如何解决？

Question

调试的时候发现我需要的指针被擦掉了一部分，导致了这个错误。但我不明白为什么“i”或“j”声明这样做...

我的代码

#include <stdio.h>
#include <stdbool.h>
#include <malloc.h>

typedef unsigned long bitset_index_t;

typedef struct
{
    bitset_index_t index;
    unsigned short *vyraz;

} bitset_t;

void bitset_alloc(bitset_t **pole, unsigned int velikost)
{
    if (velikost < 1)
    {
        // todo error
    }
    bitset_t new_bitset = {.index = 0, .vyraz = NULL};
    new_bitset.vyraz = malloc(sizeof(unsigned short) * velikost);
    if (new_bitset.vyraz == NULL)
    {
        // todo error
    }
    memset(new_bitset.vyraz, 0, sizeof(unsigned short) * (velikost));

    for (unsigned int i = 0; i < velikost; ++i)
    {

        new_bitset.vyraz[i] = 0;
        new_bitset.index++;
    }
    *pole = &new_bitset;
}

void Eratosthenes(bitset_t *pole)
{
    pole->vyraz[0] = 1;
    pole->vyraz[0] = 1;

    unsigned long velikost = pole->index;
    for (unsigned long i = 2; i < velikost; i++)
    {
        for (unsigned long j = i; j * i < velikost + 1; j++)
        {
            if (pole->vyraz[i])
                break;
            pole->vyraz[i * j] = 1;
        }
    }
    unsigned short count_prvocisel = 0;
    for (unsigned long i = pole->index; i > 0; i--)
    {
        if (count_prvocisel < 10)
        {
            if (pole->vyraz[i])
                continue;
            printf("%lu ", i);
            count_prvocisel++;
        }
        else
            break;
    }
}

int main()
{
    bitset_t *test = NULL;

    bitset_alloc(&test, 10);

    Eratosthenes(test);
}

这是第一次循环前的数据enter image description here

这是错误发生的时间enter image description here

Answer 1

你有'returned'一个局部变量的地址

void bitset_alloc(bitset_t** pole, unsigned int velikost)
{
    if (velikost < 1)
    {
        // todo error
    }
    bitset_t new_bitset = { .index = 0, .vyraz = NULL }; <<<<========
    new_bitset.vyraz = malloc(sizeof(unsigned short) * velikost);
    if (new_bitset.vyraz == NULL)
    {
        // todo error
    }
    memset(new_bitset.vyraz, 0, sizeof(unsigned short) * (velikost));

    for (unsigned int i = 0; i < velikost; ++i)
    {

        new_bitset.vyraz[i] = 0;
        new_bitset.index++;
    }
    *pole = &new_bitset; <<<<<=========

}

'new_bitset' 是一个局部变量，一旦这个函数退出就会被释放，保存它的值 - 有效地返回它 - 是无效的并导致 UB.

也可以对其进行 malloc 或在 'main'

中创建它

Segmentation fault (core dumped) - 部分指针被覆盖，如何解决？

Segmentation fault (core dumped) - part of the pointer is overwritten, how to solve it?

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