C-realloc() : invalid pointer error encoutered

Question

我一直在尝试 O(n ^2) 排序算法只是为了练习 C，但遇到了这个恼人的“realloc():无效指针”错误，并且无法找出原因。我看过其他解释，但它们没有太大帮助。

    #include <stdio.h>
    #include <stdlib.h>

    int* removeIndex(int* list, int index, int len){
        for(int i = index; i < len - 1; i++){
            list[i] = list[i+1];
        }
        return realloc(list, len - 1);
    }

    int* sort(int* unsorted, int len){
         int* sorted = malloc(len * sizeof(int));

         for(int placement = 0; placement < len; placement++){
             int smallest_index = 0;
             int smallest = unsorted[smallest_index];
             int len_unsorted = len - placement;

             for(int i = 0; i < len_unsorted; i++){
                if (unsorted[i] < smallest){
                    smallest = unsorted[i];
                    smallest_index = i;
                }    
             }

             unsorted = removeIndex(unsorted, smallest_index, len_unsorted);
             sorted[placement] = smallest;
         }

        return sorted;
    }

    int main()
    {
        int len = 5;
        int unsorted[5] = {5,4,3,2,1};

        int* sorted = sort(unsorted, len);

        for(int i = 0; i < len; i++){
            printf("%d\n", sorted[i]);
        }
        return 0;
    }

顺便说一句，为什么我写的时候会出现错误

int len = 5;
int unsorted[len] = {5,4,3,2,1};

所以我必须强制将其写为 int unsorted[5] = {5,4,3,2,1};

干杯

Answer 1

传递给realloc的指针指向一个具有自动存储持续时间的数组，该数组在main()中声明和初始化，而不是指向先前分配的内存块使用 malloc、calloc 或 realloc。

来自realloc [强调]

Reallocates the given area of memory. It must be previously allocated by malloc(), calloc() or realloc() and not yet freed with a call to free or realloc. Otherwise, the results are undefined.