pointer in C#

[amitmohanty]

Can anyone tell me if there is something like pointer in C#. If I want to interchange two rows in a mtrix which is the most efficient way? In C, probabaly we can use, if we wan to elliminate the extensive use of the stoarage space. Regards, Amit

[Judah Gabriel Himango]

You can use regular old pointers in C#. You just have to do it in an unsafe context:

unsafe static void WriteLocations()
{
int *p;
int i;
i = 10;
p = &i;

string addr;
addr = int.Format((int) p, "X");
//To Format the Pointer to a String

Console.WriteLine(addr);
Console.WriteLine(*p);

*p = 333;
Console.WriteLine(i);
//Change the Value using Pointer

i = *(&i) + 10;
Console.WriteLine(i);

}

Also, instead of marking a class or function as static, you can mark portions of code as unsafe:

void DoSomething() // safe function
{
unsafe // unsafe block of code in safe function
{
// use pointers here
}
}

Also note that the C# compiler needs the /unsafe switch turned on in order to use unsafe code.

Tech, life, family, faith: Give me a visit. I'm currently blogging about: Homosexuality in Christianity Judah Himango

[amitmohanty]

Thanks Judah! How can one function be unsafe? what is a unsafe code. regards, Amit

[Judah Gabriel Himango]

Unsafe code is

• code that cannot be verified as type-safe by the .NET Common Language Runtime (CLR).
• is not Common Language Specification (CLS)-compliant, meaning that other .NET languages like VB.NET, J#, and so on are not required to implement nor are they guaranteed to consume such code, if it were declared as public and made available to other .NET dlls & executables.
• requires a full trust security scenario in order to run, for instance, it must be installed/run from the target machine; if you try to use pointers in code run in a partial-trust scenario (e.g. a C# applet over the internet), the .NET CLR will throw a SecurityException because pointers require full access to the machine's memory, thus are potentially dangerous to the end user.
  For a function, class, or code block to be unsafe, just use the unsafe keyword:

unsafe class MyClass
{
}

unsafe void MyFunction()
{
}

void MyFunctionWithUnsafeBlock
{

unsafe
{
}

}

Despite all these cautions, you're free to use pointers as much as you like if your application is a standalone app or dll, indeed, the .NET framework uses pointers internally quite often for performance gains and interop scenarios.

Tech, life, family, faith: Give me a visit. I'm currently blogging about: Homosexuality in Christianity Judah Himango

[Guffa]

There is seldom any real need for pointers. Can't you use a reference instead? --- b { font-weight: normal; }

[amitmohanty]

I really wanted to use something which can allow me to interchange position of two rows in a 2D array. say i want to make 3rd row 7th row and place 7th row as the third row. I don't want to use a temporary 1Darray for that. If each row has say 1000 elements, then i need 1000 temporary varibale to do the calculation. I don't want to do that.

[Guffa]

What does the array contain? If it contains objects, it's really an array of references. Then you can easily exchange different elements in the array. --- b { font-weight: normal; }

[amitmohanty]

Ironically, it contains double precision numerical value. Is there a way? How can I change the reference if it consists of objects. Regards, Amit

[3Dizard]

Well, arrays in C# can be seen as pointers. If you copy one via assigning another one (e.g. a1 = a2) then you don't get a real copy a2, you just get a new reference. Greetings

[Guffa]

A double is a value type, not an object, so the array does not contain references. You have to exchange the values. --- b { font-weight: normal; }