如果我有一个如下所示的数组:
int map[21][28] =
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 2, 2, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
我如何创建一个由该数组中的值组成的较小数组......?
有点像这样:
int zoomedMap[7][7] =
{
2, 2, 1, 1, 1, 1, 1,
1, 0, 0, 0, 0, 0, 1,
1, 0, 0, 0, 0, 0, 1,
1, 0, 0, 0, 0, 0, 1,
1, 0, 0, 0, 0, 0, 1,
1, 0, 0, 0, 0, 0, 1,
1, 1, 1, 1, 1, 1, 1
};
我不知道这是否有帮助,但是:
- 我知道两个数组的确切尺寸
- 我希望可以移动较小的数组位置,最好是仅更改 X/Y 值
最佳答案
希望显而易见的是,您的子数组实际上只不过是您的主数组中的一个数据“ block ”(带有一些有趣的分区)。假设您正在检查边界并且不允许发生越界情况,您可以使用指针数学和有关主数组的一些基本信息来模拟子数组。
- 该 block 将
始终是从 [0][0]
位置偏移的一些[行][列]
,因此我们需要这些值(行和列)。 - 该 block 具有固定宽度,因此
column+width
不会超过您的主数组宽度。我们需要那个宽度。 - 该 block 具有固定高度,因此
row+height
不会超过您的主数组高度。我们需要那个高度。 - 我希望很明显我们需要作为主数组的基址(在您的例子中是
map
)。
这可能是最好的例子。以下不是最终的解决方案。它可能甚至无法满足您将要拥有的需求的 1/10。相反,它的目的是让您了解如何仅使用一个指针、一些偏移量、一些大小和一点算术来获得您正在寻找的东西。 没有什么可以阻止您超出可能有害的限制(就像普通数组一样),所以要小心。
// internal rerefential to a submatrix in a larger fixed matrix.
template<typename T>
class Sub2D
{
public:
template<size_t R, size_t C>
Sub2D(T(&ar)[R][C], int top, int left, int height, int width)
: parent(ar[0])
, row(top)
, col(left)
, max_row(R)
, max_col(C)
{
if ((row+width) >= R || (col+height) >= C)
throw std::out_of_range("");
}
// retrieve our subrow offset into the main 2D array
T* operator [](size_t n)
{
// enable at your desire, but as Alex pointed out, all
// the standard containers let you shoot yourself in the
// foot with this operator. why not this one too =P
//if (row+n >= max_row)
// throw std::out_of_range("");
return parent + ((row+n)*max_col + col);
}
private:
T* parent;
size_t row, col;
size_t max_row, max_col;
};
像这样使用,假设您问题中的数组是我们基于的数组:
int main()
{
// take the submatrix & [6][7] that is 7x7 in dimension.
Sub2D<int> sub(map, 6,7, 7,7);
for (size_t i=0;i<7;++i)
{
for (size_t j=0;j<7;++j)
cout << sub[i][j] << ' ';
cout << endl;
}
cout << endl;
// update an element at location [1][1] of our sub-matrix.
sub[1][1] = 9;
// reprint the *entire* main array. it better have updated.
for (size_t i=0;i<sizeof(map)/sizeof(map[0]);++i)
{
for (size_t j=0;j<sizeof(map[0])/sizeof(map[0][0]);++j)
cout << map[i][j] << ' ';
cout << endl;
}
cout << endl;
return 0;
}
产生以下输出。
2 2 1 1 1 1 1
1 0 0 0 0 0 1
1 0 0 0 0 0 1
1 0 0 0 0 0 1
1 0 0 0 0 0 1
1 0 0 0 0 0 1
1 1 1 1 1 1 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 2 2 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 9 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
请注意 9 现在正好位于我们预期的位置。
显然,您可以向这样的模板类中添加更多内容,包括更好的范围检查、移动指针、快照到其他内存缓冲区等,但关键是基本的 get-me-this 子矩阵一个指针和几个偏移量很难被击败,尤其是在性能方面。
关于c++ - 由另一个数组中的值组成的数组,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14302316/