为什么同时具有锯齿状数组和多维数组？ [英] Why we have both jagged array and multidimensional array?

问题描述

1. 锯齿状数组和多维数组有什么区别。
   彼此有益吗？

1. What is the difference between jagged array and Multidimensional array. Is there a benefit of one on another?

为什么Visual Studio不允许我做

And why would the Visual Studio not allow me to do a

MyClass[][] abc = new MyClass[10][20];

（我们以前在C ++中这样做，但是在C＃中用红色的蠕动线强调[20] ..表示无效的排名说明符）

(We used to do that in C++, but in C# it underlines [20] with red wriggly line.. Says invalid rank specifier)

，但对

MyClass[,] abc = new MyClass[10,20];

最后如何在一行中初始化它（就像我们在简单数组中用 {新xxx ...} {新xxx ....} ）

MyClass[][,][,] itemscollection;

推荐答案

1. 锯齿状数组是数组数组，因此 int [] [] 是<$ c $数组c> int [] ，每个长度可以不同，并在内存中占据各自的块。多维数组（ int [，] ）是一个内存块（本质上是一个矩阵）。

1. A jagged array is an array-of-arrays, so an int[][] is an array of int[], each of which can be of different lengths and occupy their own block in memory. A multidimensional array (int[,]) is a single block of memory (essentially a matrix).

您不能创建 MyClass [10] [20] ，因为每个子数组都必须分别初始化，因为它们是单独的对象：

You can't create a MyClass[10][20] because each sub-array has to be initialized separately, as they are separate objects:

MyClass[][] abc = new MyClass[10][];

for (int i=0; i<abc.Length; i++) {
    abc[i] = new MyClass[20];
}

A MyClass [10,20] 可以，因为它正在将单个对象初始化为具有10行20列的矩阵。

A MyClass[10,20] is ok, because it is initializing a single object as a matrix with 10 rows and 20 columns.

A MyClass [] [，] [，] 可以这样初始化（尽管未进行编译测试）：

A MyClass[][,][,] can be initialized like so (not compile tested though):

MyClass[][,][,] abc = new MyClass[10][,][,];

for (int i=0; i<abc.Length; i++) {
    abc[i] = new MyClass[20,30][,];

    for (int j=0; j<abc[i].GetLength(0); j++) {
        for (int k=0; k<abc[i].GetLength(1); k++) {
            abc[i][j,k] = new MyClass[40,50];
        }
    }
}

请记住，CLR已针对单维数组访问进行了优化，因此使用锯齿状数组可能比相同大小的多维数组要快。

Bear in mind, that the CLR is heavily optimized for single-dimension array access, so using a jagged array will likely be faster than a multidimensional array of the same size.

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