C++ "was not declared in this scope"编译错误

Question

C++ 新手。在我编写的以下程序中出现此错误:

g++ -o Blob blob.cc
blob.cc: In function 'int nonrecursivecountcells(color (*)[7], int, int)':
blob.cc:41: error: 'grid' was not declared in this scope

代码如下:

#include <iostream>
enum color {BACKGROUND, ABNORMAL, TEMPORARY};
const int ROW_SIZE = 7;
const int COL_SIZE = 7;
int nonrecursivecountcells(color[ROW_SIZE][COL_SIZE], int, int);
using namespace std;


int main() 
{
  color grid[ROW_SIZE][COL_SIZE] =
    {{BACKGROUND, ABNORMAL, BACKGROUND, ABNORMAL, BACKGROUND, BACKGROUND, BACKGROUND},
      {ABNORMAL, ABNORMAL, BACKGROUND, ABNORMAL, BACKGROUND, BACKGROUND, BACKGROUND},
       {BACKGROUND, BACKGROUND, ABNORMAL, ABNORMAL, BACKGROUND, BACKGROUND, ABNORMAL},
        {BACKGROUND, BACKGROUND, BACKGROUND, ABNORMAL, ABNORMAL, ABNORMAL, BACKGROUND},
         {BACKGROUND, BACKGROUND, BACKGROUND, ABNORMAL, BACKGROUND, BACKGROUND, BACKGROUND},
          {BACKGROUND, BACKGROUND, BACKGROUND, BACKGROUND, BACKGROUND, ABNORMAL, BACKGROUND},
           {BACKGROUND, ABNORMAL, ABNORMAL, BACKGROUND, BACKGROUND, BACKGROUND, ABNORMAL}};

   cout << "Enter row number" << endl;
   int row;
   cin >> row;
   cout << "Enter column number" << endl;
   int column;
   cin >> column;

   int number = nonrecursivecountcells(grid, row, column);
   cout << "Number off cells in the blob that contains grid[" << row << "][" << column << "] are: " << number << endl;

   return 0;

}

int nonrecursivecountcells(color[ROW_SIZE][COL_SIZE], int row, int column)
{
  if (row < 0 || row >= ROW_SIZE || column < 0 || column >= COL_SIZE)
  {
    return 0;
  }

  else if (grid[row][column] != ABNORMAL)
  {
    return 0;
  }

  else
  {
    grid[row][column] = TEMPORARY;
    return 1
    + nonrecursivecountcells(grid, row - 1, column - 1) + nonrecursivecountcells(grid, row - 1, column)
    + nonrecursivecountcells(grid, row - 1, column + 1) + nonrecursivecountcells(grid, row, column + 1)
    + nonrecursivecountcells(grid, row + 1, column + 1) + nonrecursivecountcells(grid, row + 1, column)
    + nonrecursivecountcells(grid, row + 1, column - 1) + nonrecursivecountcells(grid, row, column - 1);
  }
}

有人可以帮我吗？谢谢。

Answer 1

出了什么问题:

“nonrecursivecountcells”的定义没有名为 grid 的参数。您需要将类型和变量名传递给函数。你只传递了类型。

请注意，如果您使用名称 grid 作为参数，则该名称与 grid 的 main() 声明无关。您也可以使用任何其他名称。

***Also you can't pass arrays as values.

---

如何修复:

解决此问题的简单方法是将指向数组的指针传递给函数“nonrecursivecountcells”。

int nonrecursivecountcells(color[ROW_SIZE][COL_SIZE], int, int);

更好并且类型安全 ->

int nonrecursivecountcells(color (&grid)[ROW_SIZE][COL_SIZE], int, int);

关于范围:

当声明它的 block 终止时，在堆栈上创建的变量超出范围。 block 是位于左括号和匹配 右括号内的任何内容。例如 if() { }, function() { }, while() {}, ...

注意我说的是变量而不是数据。例如，您可以在堆上分配内存，即使在范围之外，该数据仍然有效。但是最初指向它的变量仍然会超出范围。