当我尝试重新分配（）结构指针数组时，为什么我的 C 程序会崩溃？

Question

In the code below, I'm trying to expand an array of key value structs using realloc().

#include <stdio.h>
#include <string.h>

typedef struct {
    char key[25];
    char value[25];
} keyValPair;

void inputKeyVal(keyValPair* arr, int n) {
    char inputKey[25];
    char inputVal[25];
    printf("input key: ");
    scanf(" %24s", &inputKey);
    printf("input value: ");
    scanf(" %24s", &inputVal);
    n++;
    arr = (keyValPair*) realloc( (keyValPair*) arr, n*sizeof(keyValPair));
    strcpy(arr[n-1].key, inputKey);
    strcpy(arr[n-1].value, inputVal);
}

int main() {
    keyValPair initArr[] = {{"foo", "bar"}, {"a", "b"}};
    int n = sizeof(initArr)/sizeof(keyValPair);
    keyValPair* arr = malloc(n * sizeof(keyValPair));
    arr = initArr;
    inputKeyVal(arr, n);
}

Whenever I run it however, it runs up to the input prompt, before crashing at the realloc() attempt. I still can't figure out why or how to fix it. Fairly new to C, so a detailed explanation would be much appreciated and would go a long way.

Answer 1

I think that there are three problems.

arr = initArr; overwrites the address of arr by initArr , so that realloc can't take the address which has been allocated by malloc . To keep the address allocated by malloc , the contents of initArr should be copied into arr .

#include <stddef.h>

for (size_t i = 0; i < sizeof(initArr) / sizeof(initArr[0]); i++) {
   arr[i] = initArr[i];
}

The last argument for scanf is wrong. & is unnecessary.

scanf("%24s", inputKey);

After inputKeyVal , arr at main loses valid address because it is reallocated in inputKeyVal . If you require the correct address which has been reallocated by realloc , inputKeyVal should return the reallocated address.

keyValPair* inputKeyVal(keyValPair* arr, int n) {
  /* snipped */
  return arr;
}

int main() {
  /* snipped */
  arr = inputKeyVal(arr, n);
  /* do something for arr */
  free(arr);
  return 0;
}