c++ - 使用指针数组的函数

Question

我的 C++ 作业中有这个问题。

Write and test the function location that takes, as shown below, a table of pointers to integers p, the size of such a table n and an integer value x.

                      int* location (int* p [ ], int n, int x);

location searches the set of integers pointed at by the table of pointers p for a match to the value of x. If a matching integer is found, then location returns the address of that integer, NULL otherwise.

我不确定我是否完全理解这个问题。但是，我试图解决它但出现错误(程序崩溃)。这是我的代码。

#include<iostream>
using namespace std;
int* location (int* p [ ], int n, int x);
void main(){
    int arr[3]={1,2,3};
    int *ptr=arr;
    int *address= location (&ptr, 3, 2);
    cout<<&arr[3]<<" should be equal to "<<address<<endl;
}
int* location (int* p [ ], int n, int x){
    for(int i=0; i<n; i++){
        if(*p[i]==x){return p[i];}
    }

    return NULL;

}

有人可以告诉我我的错误或者告诉我我是否正确地解决了这个问题？

谢谢

Answer 1

这在您的代码中是不正确的:

cout<<&arr[3]<<" should be equal to "<<address<<endl;

您正在访问索引为 3 的数组元素，但是，在您的情况下您可以访问的最大索引为 2。此外，下面还有替代解决方案。

此外，您将指针传递给指向您的 location 函数的指针(以及使用它)的方式也是错误的。因为例如您没有首先声明指向整数的指针数组。

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您可以尝试阅读更多有关 C++ 中指针数组概念的内容，以便更好地理解下面的示例。

#include <iostream>

using namespace std;
const int MAX = 3;

int* location (int* p [ ], int n, int x);

int main ()
{
   int  var[MAX] = {10, 100, 200};

   // Declare array of pointers to integers
   int *ptr[MAX];

   for (int i = 0; i < MAX; i++)
   {
      ptr[i] = &var[i]; // Store addresses of integers
   }

   int *x = location(ptr, MAX, 100); // Now you have pointer to the integer you were looking for, you can print its value for example
   if(x != NULL) cout<<*x;

   return 0;
}

int* location (int* p [ ], int n, int x)
{
  for(int i = 0; i<n; i++)
  { 
     if(*p[i] == x) return p[i];
  }

 return NULL;
}