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==Accessing Structure Members with a Pointer==

<source lang="csharp">using System;

public struct Point2D
{
public int X;
public int Y;
}

public class MyClass
{
public unsafe static void Main()
{
Point2D MyPoint;
Point2D * PointerToMyPoint;

MyPoint = new Point2D();
PointerToMyPoint = &MyPoint;
PointerToMyPoint->X = 100;
PointerToMyPoint->Y = 200;
Console.WriteLine("({0}, {1})", PointerToMyPoint->X, PointerToMyPoint->Y);
}
}</source>

==Compile unsafe code==

<source lang="csharp">// compile with: csc /unsafe ReadFileUnsafe.cs</source>

==Mark method as unsafe to pointers==

<source lang="csharp">using System;

class UnsafeCode {
unsafe public static void Main() {
int count = 99;
int* p; // create an int pointer

p = &count; // put address of count into p

Console.WriteLine("Initial value of count is " + *p);

*p = 10; // assign 10 to count via p

Console.WriteLine("New value of count is " + *p);
}
}</source>
<pre class=codeResult>Initial value of count is 99
New value of count is 10</pre>

==unsafe block==

<source lang="csharp">public struct MyValue
{
private int id;
private decimal price;
public MyValue(int id, decimal price)
{
this.id = id;
this.price = price;
}
override public string ToString()
{
return String.Format("{0}: {1}", id, price);
}

unsafe public static void Swap(MyValue* pi, MyValue* pj)
{
MyValue tmp = *pi;
*pi = *pj;
*pj = tmp;
}
}

class UnsafeStructApp
{
static void Main(string[] args)
{
MyValue i = new MyValue(123, 45.67m);
MyValue j = new MyValue(890, 98.76m);
Console.WriteLine("Before Swap:\ti = {0}, j = {1}", i, j);

unsafe { MyValue.Swap(&i, &j); }
Console.WriteLine("After Swap:\ti = {0}, j = {1}", i, j);
}
}</source>

==Unsafe Code==

<OL><LI>C# allows you to write "unsafe" code.</LI><LI>Unsafe code does not execute under the full management of the Common Language Runtime (CLR).</LI><LI>Unsafe code often involves the use of pointers.</LI><LI>Pointers are a bit like references in C#.</LI><LI>The main difference is that a pointer can point anywhere in memory</LI><LI>A reference always points to an object of its type.</LI><LI>To compile unmanaged code, you must use the /unsafe compiler option.</LI></OL>
33.1.unsafe
33.1.1.
Unsafe Code
33.1.2.
<A href="/Tutorial/CSharp/0620__unsafe/Compileunsafecode.htm">Compile unsafe code</a>
33.1.3.
<A href="/Tutorial/CSharp/0620__unsafe/Usingunsafeandfixed.htm">Using unsafe and fixed</a>
33.1.4.
<A href="/Tutorial/CSharp/0620__unsafe/Markmethodasunsafetopointers.htm">Mark method as unsafe to pointers</a>
33.1.5.
<A href="/Tutorial/CSharp/0620__unsafe/AccessingStructureMemberswithaPointer.htm">Accessing Structure Members with a Pointer</a>
33.1.6.
<A href="/Tutorial/CSharp/0620__unsafe/UnsafeMethods.htm">Unsafe Methods</a>
33.1.7.
<A href="/Tutorial/CSharp/0620__unsafe/Usingtheunsafekeyword.htm">Using the unsafe keyword.</a>
33.1.8.
<A href="/Tutorial/CSharp/0620__unsafe/unsafeblock.htm">unsafe block</a>

==Unsafe Methods==

<source lang="csharp">using System;

public class MyClass
{
public unsafe static void Main()
{
int MyInteger = 123;
int * MyIntegerPointer = &MyInteger;

Console.WriteLine(*MyIntegerPointer);
}
}</source>

==Using the unsafe keyword.==

<source lang="csharp">using System;
class MainClass {
public static unsafe String UnsafeCodeExample(String s) {
int len = s.Length;
char[] str = new char[len + 1];
string stemp = "";
int nPos = 0;
fixed (char* sptr = str) {
// Copy the string in backward
for (int i = len - 1; i >= 0; --i) {
sptr[nPos++] = s[i];
sptr[nPos] = (char)0;
}
// Now, copy it back
for (int i = 0; i < len; ++i)
stemp += sptr[i];
}
return stemp;
}
public static void Main() {
String s = UnsafeCodeExample("This is a test");
Console.WriteLine("Reversed: {0}", s);
}
}</source>

==Using unsafe and fixed==

<OL><LI>Any code that uses pointers must be marked as unsafe by using the unsafe keyword.</LI><LI>You can mark an individual statement or an entire method unsafe.</LI></OL>
<OL><LI>The fixed modifier is often used when working with pointers.</LI><LI>The fixed modifier prevents a managed variable from being moved by the garbage collector.</LI></OL>
33.1.unsafe
33.1.1.
<A href="/Tutorial/CSharp/0620__unsafe/UnsafeCode.htm">Unsafe Code</a>
33.1.2.
<A href="/Tutorial/CSharp/0620__unsafe/Compileunsafecode.htm">Compile unsafe code</a>
33.1.3.
Using unsafe and fixed
33.1.4.
<A href="/Tutorial/CSharp/0620__unsafe/Markmethodasunsafetopointers.htm">Mark method as unsafe to pointers</a>
33.1.5.
<A href="/Tutorial/CSharp/0620__unsafe/AccessingStructureMemberswithaPointer.htm">Accessing Structure Members with a Pointer</a>
33.1.6.
<A href="/Tutorial/CSharp/0620__unsafe/UnsafeMethods.htm">Unsafe Methods</a>
33.1.7.
<A href="/Tutorial/CSharp/0620__unsafe/Usingtheunsafekeyword.htm">Using the unsafe keyword.</a>
33.1.8.
<A href="/Tutorial/CSharp/0620__unsafe/unsafeblock.htm">unsafe block</a>

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в 15:31, 26 мая 2010

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