Question

2D阵列与阵列之间的区别是什么?

我阅读了似乎区分两种意见的评论:

int** arr = ...;
cout << arr[i][j];
如果他使用2个阵列,或点对称型,而不是一系列阵列——@Dave

Answer 1

2个层面阵列is,按定义分为一系列阵列。

What Dave was saying is that in that context, there are different semantics between the definition of a 2D array like 因此:

int x[][];

因此:

int *x[];

or 因此:

int **x;

Answer 2

这里有四个不同的概念。

The two-dimensional array: int arr[][]. It cannot be resized in any direction, and is contiguous. Indexing it is the same as ((int*)arr)[y*w + x]. Must be allocated statically.
The pointer-to array: int (*arr)[]. It can be resized only to add more rows, and is contiguous. Indexing it is the same as ((int*)arr)[y*w + x]. Must be allocated dynamically, but can be freed free(x);
The pointer-to-pointer: int **arr. It can be resized in any direction, and isn t necessarily square. Usually allocated dynamically, not necessarily contiguous, and freeing is dependent on its construction. Indexing is the same as *(*(arr+y)+x).
The array-of-pointers: int *arr[]. It can be resized only to add more columns, and isn t necessarily square. Resizing and freeing also depends on construction. Indexing is the same as *(*(arr+y)+x).

每一条均可使用<代码>arr[y][x],造成混乱。

Answer 3

这里的答案略为微妙。

界定了一系列阵列:

int array2[][];

点对线类型的定义是:

int (*array2)[];

点数类型的定义是:

int* array2[];

汇编者对这两种方法的处理差别不大,实际上还有一种选择:

int** array2;

许多人被教授说,这三人是相同的,但如果你们更多地了解汇编者,你肯定会知道,差异很小,但确实存在。如果你替代另一个方案,那么许多方案将运作起来,但是,在汇编者和阿盟一级,东西都是东塔。汇编者手册应当提供更深入的答案。

此外,如果有人对2D阵列的实施感兴趣,则根据情况,有多种方法在效率上有所不同。你们可以把2D阵列图成1D阵列,确保在处理线性数据时保持距离。如果你想要方便方案规划,如果你需要单独操纵浏览/栏目,你可以使用阵列。某些被阻塞的类型和其他胎图是切除的,但是如果用户是的话,你很少需要知道。

我希望!

Answer 4

下面是可称为阵列的2D阵列:

int AoA[10][10];

下面是作为2D阵列运作的协调人:

int **P2P = malloc(10 * sizeof *P2P);
if(!P2P) exit(1);
for(size_t i = 0; i < 10; i++)
  {
    P2P[i] = malloc(10 * sizeof **P2P);
    if(!P2P[i])
      {
        for(; i > 0; i--)
            free(P2P[i - 1]);
        free(P2P); 
      }
  }

两者均可通过<代码>AoA[x][y]或P2P[x][y]获取,但两者互不相容。具体来说,<代码>P2P = AoA 是新bies有时预期会奏效的,但不会——<代码>P2P预期指点人,但当代码 decays into a pointer时,该编号为 /em> ,具体来说是int (*)[10],而不是<编码>/<<<<>>>>>>>>>>>>/code>。

Answer 5

2个阵列可以包括:

int x[width * height]; // access: x[x + y * width];

来自Wikipedia:

For a two-dimensional array, the element with indices i,j would have address B + c · i + d · j, where the coefficients c and d are the row and column address increments, respectively.

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