為什么在嘗試將指向數組的指針作為函數的參數時出現訪問沖突錯誤？

Question

當我嘗試遍歷“星期五”數組時出現訪問沖突錯誤。

我試圖在while循環之前檢查空指針，但仍然...

int lostSheep(const int *friday, const int* saturday, int total)
{
    int friSum = 0;
    int satSum = 0;
    int i = 0;

    while(friday + i) {
        friSum += *(friday + i);
        i++;
    }

    i = 0;
    while(saturday + i) {
        satSum += *(saturday + i);
        i++;
    }

    int sum = satSum + friSum;
    return total - sum;
}

int main() {

    int array1[] = { 1, 2 };
    int array2[] = { 3, 4 };

    printf("%d", lostSheep(array1, array2, 15));

    return 0;
}

我只想遍歷數組並將所有元素求和

Answer 1

在while(friday + i) { ，即使第一輪測試也不會出錯，因為friday不是NULL指針，因此您可以通過*(friday + i);訪問數組*(friday + i); 當我大於1時

可能是while(friday[i] != 0) {假設您使用{1, 2, 0} 1、2、0 {1, 2, 0}初始化了array1嗎？

當然， 星期六也有類似的問題

注意您也可以在參數中給出數組的大小

使用friday[i]而不是*(friday + i)更具可讀性

---

第一種可能性是添加一個空值來標記數組的結尾：

#include <stdio.h>

int lostSheep(const int *friday, const int* saturday, int total)
{
  int friSum = 0;
  int satSum = 0;
  int i = 0;
  while(friday[i]) {
    friSum += friday[i];
    i++;
  }
  i = 0;
  while(saturday[i]) {
    satSum += saturday[i];
    i++;
  }
  int sum = satSum + friSum;
  return total - sum;
}

int main() {
  int array1[] = { 1, 2, 0 };
  int array2[] = { 3, 4, 0 };

  printf("%d\n", lostSheep(array1, array2, 15));
  return 0;
}

編譯執行：

pi@raspberrypi:/tmp $ gcc -g -pedantic -Wextra c.c
pi@raspberrypi:/tmp $ ./a.out
5

---

給出數組大小的第二種可能性：

#include <stdio.h>

int lostSheep(const int *friday, size_t sz1,
              const int* saturday, size_t sz2,
              int total)
{
  int friSum = 0;
  int satSum = 0;
  size_t i;

  for (i = 0; i < sz1; ++i) {
    friSum += friday[i];
  }

  for (i = 0; i < sz2; ++i) {
    satSum += saturday[i];
  }

  int sum = satSum + friSum;

  return total - sum;
}

int main() {
  int array1[] = { 1, 2 };
  int array2[] = { 3, 4 };

  printf("%d\n", lostSheep(array1, sizeof(array1)/sizeof(int),
                           array2, sizeof(array2)/sizeof(int),
                           15));
  return 0;
}

編譯執行：

pi@raspberrypi:/tmp $ gcc -g -pedantic -Wextra c.c
pi@raspberrypi:/tmp $ ./a.out
5

在valgrind下 ：

pi@raspberrypi:/tmp $ valgrind ./a.out
==3996== Memcheck, a memory error detector
==3996== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3996== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==3996== Command: ./a.out
==3996== 
5
==3996== 
==3996== HEAP SUMMARY:
==3996==     in use at exit: 0 bytes in 0 blocks
==3996==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==3996== 
==3996== All heap blocks were freed -- no leaks are possible
==3996== 
==3996== For counts of detected and suppressed errors, rerun with: -v
==3996== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)
p

---

注意將friSum和satSum分開以最終將它們相加是復雜的，僅具有唯一的和更簡單，也可能沒有和並直接遞減總計

int lostSheep(const int *friday, size_t sz1,
              const int* saturday, size_t sz2,
              int total)
{
  size_t i;

  for (i = 0; i < sz1; ++i) {
    total -= friday[i];
  }

  for (i = 0; i < sz2; ++i) {
    total -= saturday[i];
  }

  return total;
}