C中的不对称多维数组

发布于 2024-11-02 22:35:52 字数 455 浏览 1 评论 0原文

我正在将一段代码从 PHP 移植到 c/objective-c，并且在处理这个二维数组时遇到了麻烦。

$PATTERN_LOOKUP = array(
    array(),
    array(6, 18),
    array(6, 22, 38),
    array(6, 26, 46, 66),
    array(6, 28, 50, 72, 94)
);

这是我得到的最接近的（它可以编译），但是我想稍后会遇到麻烦，因为这实际上是一个 5x5 数组，并且会有一堆未定义的数字。有没有办法在c中制作不对称的多维数组？

static int PATTERN_LOOKUP[][5] = {
    {0},
    {6, 18},
    {6, 22, 38},
    {6, 26, 46, 66},
    {6, 28, 50, 72, 94}
};

原文

I'm porting a piece of code from PHP to c/objective-c, and I'm running into trouble handling this two dimensional array.

$PATTERN_LOOKUP = array(
    array(),
    array(6, 18),
    array(6, 22, 38),
    array(6, 26, 46, 66),
    array(6, 28, 50, 72, 94)
);

This is the closest I've gotten (it compiles), however I'm thinking I'll run into trouble later, because this is actually a 5x5 array, and there will be a bunch of undefined numbers. Is there a way to make an asymmetrical multidimensional array in c?

static int PATTERN_LOOKUP[][5] = {
    {0},
    {6, 18},
    {6, 22, 38},
    {6, 26, 46, 66},
    {6, 28, 50, 72, 94}
};

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墨离汐 2024-11-09 22:35:52

好吧，你总是可以在 C 中创建一个“对称”数组（即矩形数组），并且只使用它的“不对称”部分。对于小型阵列来说，这是一个完美的解决方案。这实际上正是您的 PATTERN_LOOKUP 声明所做的（未显式初始化的元素将用零隐式初始化）。

然而，对于较大的阵列，由于浪费内存，它可能会变得过于昂贵。如果它确实变得太昂贵，您始终可以在 C 中使用“模拟”2D 数组（指向子数组的指针数组）

static int array0[] = { 0 };
static int array1[] = { 6, 18 };
static int array2[] = { 6, 22, 38 };
static int array3[] = { 6, 26, 46, 66 };
static int array4[] = { 6, 28, 50, 72, 94 };

static int *const PATTERN_LOOKUP[] = {
  array0,
  array1,
  array2,
  array3,
  array4
};

您甚至可以在 PATTERN_LOOKUP 中使用 NULL 条目array 来表示空数组

static int *const PATTERN_LOOKUP[] = {
  NULL,
  array1,
  array2,
  array3,
  array4
};

在 C99 中，您可以使用复合文字来获得相同的结果，而无需单独的子数组声明。

static int *const PATTERN_LOOKUP[] = {
  (int []) { 0 },
  (int []) { 6, 18 },
  (int []) { 6, 22, 38 },
  (int []) { 6, 26, 46, 66 },
  (int []) { 6, 28, 50, 72, 94 }
};

当然，存储/记住每个单独子数组的实际大小仍然是您的责任。

Well, you can always make a "symmetrical" array in C (i.e. a rectangular array) and only use an "asymmetrical" portion of it. This is a perfectly good solution for small arrays. And this is actually exactly what your declaration of PATTERN_LOOKUP does (the elements not explicitly initialized will be implicitly initialized with zeros).

However, for larger arrays it might get too expensive in therms of wasted memory. If it does get too expensive, you can always use a "simulated" 2D array in C (an array of pointers to subarrays)

static int array0[] = { 0 };
static int array1[] = { 6, 18 };
static int array2[] = { 6, 22, 38 };
static int array3[] = { 6, 26, 46, 66 };
static int array4[] = { 6, 28, 50, 72, 94 };

static int *const PATTERN_LOOKUP[] = {
  array0,
  array1,
  array2,
  array3,
  array4
};

You can even use a NULL entry in PATTERN_LOOKUP array to represent an empty array

static int *const PATTERN_LOOKUP[] = {
  NULL,
  array1,
  array2,
  array3,
  array4
};

In C99 you can use compound literals to achieve the same result without separate subarray declarations

static int *const PATTERN_LOOKUP[] = {
  (int []) { 0 },
  (int []) { 6, 18 },
  (int []) { 6, 22, 38 },
  (int []) { 6, 26, 46, 66 },
  (int []) { 6, 28, 50, 72, 94 }
};

Of course, it remains your responsibility to store/remember the actual size of each individual subarray.

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