# Detailed explanation of simulation array out of bounds under. Net

Time：2019-10-18

Preface

The previous article mentioned array overrun behavior, although the compiler did a lot of checking for us to avoid these errors.

But I think it’s still necessary to simulate the array out of bounds and feel the error.

So for. Net, how can we simulate array overrun?

I. [vs] item – > right click – > Property – > generate – > check to allow unsafe code II. Test code

``````
unsafe private static void OutOfIndexMini()
{
int* i = stackalloc int;

i = 0;
//i = 1;

//double* d = stackalloc double;
//d = 0.01;

int* a = stackalloc int;

for (; i <= 3; i++)
{
a[i] = 0;

Console.WriteLine(\$"int* i = {i}");

Console.WriteLine(\$"int* a[{i}] = {a[i]}");
}

}``````

Briefly:

Unsafe keyword — supports unsafe code, which means we can use pointers.

Stackalloc keyword — allows memory to be requested from the stack.

Here are two sentences: I applied the array int  to memory, with the capacity of an int, and assigned the value to 1 at the same time.

``````
int* i = stackalloc int;

i = 0;``````

Next: I immediately applied for the array int  to memory, with a capacity of 3 ints.

``````
int* a = stackalloc int;``````

Then note: my for loop array is out of bounds I  < = 3

``````
for (; i <= 3; i++)
{
a[i] = 0;

Console.WriteLine(\$"int* i = {i}");

Console.WriteLine(\$"int* a[{i}] = {a[i]}");
}``````

Initial value I  = 0, so enter for loop

i = 0 >>> a[ i[ 0 ] ] =0 >>>a[ 0 ] =0

i = 1 >>> a[ i[ 0 ] ] =0 >>>a[ 1 ] =0

i = 2 >>> a[ i[ 0 ] ] =0 >>>a[ 2 ] =0

i = 3 >>> a[ i[ 0 ] ] =0 >>>a[ 3 ] =0 ?

At this time, a  for us, the array is out of bounds, but it can still be assigned normally here. So who are we giving this to?

A  actually crossed the boundary to I , that is, a  = I  = 0.

This causes that when I  = 3, a  changes I  to 0, and the program enters a dead cycle…

Three, validation

If I change the initial value of I  to 1

``````
int* i = stackalloc int;

//i = 0;
i = 1; ``````

Then a  = I  = 0 after crossing the boundary, print out I  = 0 to indicate that the array is indeed out of the boundary and modify the value. Then, I will declare an array that is not of type int in the middle, so that the out of bounds is not a modified I , so there will be no dead cycle.

``````
int* i = stackalloc int;

//i = 0;
i = 1;

double* d = stackalloc double;
d = 1;

int* a = stackalloc int;`````` IV. principle analysis

Because arrays are the same data type, continuous memory.

First time: I = 0, a  memory address 1000

The second time: I = 1, a  memory address 1004

The third time: I = 2, a  memory address 1008

The fourth time: I = 3, a  memory address 1012, that is to say, I  is crossed. summary

The above is the whole content of this article. I hope that the content of this article has a certain reference learning value for everyone’s study or work. If you have any questions, you can leave a message and exchange. Thank you for your support for developepaar.

## Query SAP multiple database table sizes

Query SAP multiple database table sizes https://www.cnblogs.com/ken-yu/p/12973009.html Item code db02 Here are two approaches, In the first graphical interface, the results of the query data table are displayed in MB, and only one table can be queried at a time. SPACE—Segments—Detailed Analysis—Detailed Analysis  In the pop-up window segment / object, enter the name of the […]