A brief analysis of C# array initialization

There are always various surprises and shocks! C# array is one of them, and I regard it as my debut blog.
C# arrays are very different from other C series languages. There was a big difference in understanding when I was exposed to them in the past. Especially the understanding of multi-dimensional arrays. Multidimensional arrays are a new concept compared to C language. At first, I regarded it as a special type of jagged array.

First focus on the initialization and access of two-dimensional arrays and simple interleaved arrays

int[,] nums={ 
{1,2,3}, 
{1,2,0} 
}; 
for (int i = nums.GetLowerBound(0); i <= nums.GetUpperBound(0); i++) 
{ 
for (int j = nums.GetLowerBound(1); j <= nums.GetUpperBound(1); j++) 
{ 
Console.WriteLine(nums[i,j]); 
Console.WriteLine(nums.GetValue(i,j)); 
} 
} 
foreach (var num in nums) 
{ 
Console.WriteLine(num); 
} 
//对任意维度的数组，都可以这样快速访问，只是foreach不能修改变量。

And interleaved arrays can also achieve similar content

int[][] nums2 ={ 
new int[]{1,2,3}, 
new int[]{1,2,0} 
}; 
for (int i = nums2.GetLowerBound(0); i <= nums2.GetUpperBound(0); i++) 
{ 
for (int j = nums2[i].GetLowerBound(0); j <= nums2[i].GetUpperBound(0); j++) 
{ 
Console.WriteLine(nums2[i][j]); 
} 
} 
foreach (var ia in nums2) 
{ 
foreach (var i in ia) 
{ 
Console.WriteLine(i); 
} 
}

The data stored in multi-dimensional arrays can be replaced by interleaved arrays. A jagged array is a special array with high dimensions. And a jagged array is an array of arrays. And arrays have a very important property,

The items stored in the array must be of the same type! This is important for understanding various complex arrays.
Complex Jagged Array

bool[][][] cells31 = new bool[2][][] 
{ 
new bool[2][] 
{ 
new bool[] {false}, 
new bool[] {true} 
}, 
new bool[3][] 
{ 
new bool[] {false}, 
new bool[] {true}， 
new bool[] {true} 
} 
};

We must initialize like this. There is a lot of new. Because the jagged array is an array of arrays, we have always nested it before. But a lot of array types are needed, and countless array types can be created.

Console.WriteLine("交错数组类型"); 
Console.WriteLine(cells31[0].GetType()); 
Console.WriteLine(cells31[0][0].GetType()); 
Console.WriteLine(cells31[0][0][0].GetType()); 
//交错数组类型 
//System.Boolean[][] 
//System.Boolean[] 
//System.Boolean 
//这是交错数组里面的类型。 
// bool[2][] 与boo[3][] 是相同的类型，所以我们创建存储结构不一致的数组

The next is the most complex type. Mix jagged arrays with multidimensional arrays. If you can initialize the array below, you should understand it more thoroughly!

bool [][,,][][,,][]Foo;
I chose a simple point as an example bool [][,][]Foo;

bool[][,][] Foo = new bool[1][,][] 
{ 
new bool[2,2][] 
{ 
{ 
new bool[2] {false, true}, 
new bool[2] {false, true} 
}, 
{ 
new bool[2] {false, true}, 
new bool[2] {false, true} 
} 
} 
}; 
Console.WriteLine("混合数组类型"); 
Console.WriteLine(Foo.GetType()); 
Console.WriteLine(Foo[0].GetType()); 
Console.WriteLine(Foo[0][0,0].GetType()); 
Console.WriteLine(Foo[0][0, 0][0].GetType()); 
//结果 混合数组类型 
//system.boolean[][,][] 
//system.boolean[][,] 
//system.boolean[] 
//system.boolean

//定义交错数组：一维数组存放（二维int数组存放（一维int数组存放（四维int数组））） 
//标准的C#定义描述 array of( multi-array of( array of (nulti-array))) 
int[][,][][, , ,] arr = new int[10][,][][,,,]; 
//初始化 二维int数组存放（一维int数组存放（四维int数组）） 
arr[4] = new int[1, 2][][,,,]; 
//初始化 一维int数组存放（四维int数组） 
arr[4][0, 1] = new int[3][, , ,]; 
//初始化 四维int数组 
arr[4][0, 1][2] = new int[1, 2, 3, 4]; 
Console.WriteLine(arr.GetType()); 
Console.WriteLine(arr[4].GetType()); 
Console.WriteLine(arr[4][0, 1].GetType()); 
Console.WriteLine(arr[4][0, 1][2].GetType()); 
//System.Int32[,,,][][,][] 
//System.Int32[,,,][][,] 
//System.Int32[,,,][] 
//System.Int32[,,,] 
//C#编译器生成的名字与我们声明的是倒着的。理解起来应该也没差异吧

It should be clearer now. I don't know if every programmer understands this, but it took me a lot of time to understand it.

Finally, consider the impact on array methods. Especially Clear();

Console.WriteLine(Foo[0][0,0][0]); 
//输出为Flase 
Array.Clear(Foo,0,1); 
Console.WriteLine(Foo[0][0, 0][0]); 
//这里会引发空引用异常。因为 bool[][,]的类型的值已经变为null。

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