为什么在尝试将指向数组的指针作为函数的参数时出现访问冲突错误？

Question

当我尝试遍历“星期五”数组时出现访问冲突错误。

我试图在while循环之前检查空指针，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;
}

我只想遍历数组并将所有元素求和

Answer 1

在while(friday + i) { ，即使第一轮测试也不会出错，因为friday不是NULL指针，因此您可以通过*(friday + i);访问数组*(friday + i); 当我大于1时

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

当然， 星期六也有类似的问题

注意您也可以在参数中给出数组的大小

使用friday[i]而不是*(friday + i)更具可读性

---

第一种可能性是添加一个空值来标记数组的结尾：

#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;
}

编译执行：

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

---

给出数组大小的第二种可能性：

#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;
}

编译执行：

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

---

注意将friSum和satSum分开以最终将它们相加是复杂的，仅具有唯一的和更简单，也可能没有和并直接递减总计

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;
}