CSharp/C# Tutorial - C# Unsafe Code Pointers

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C# can do direct memory manipulation via pointers within blocks of code marked unsafe.

The unsafe code should be compiled with the /unsafe compiler option.

Pointer Basics

A pointer instance holds the address of a variable.

Pointer types can be cast to any other pointer type.

The main pointer operators are:

Unsafe Code

By marking a type, type member, or statement block with the unsafe keyword, we can use pointer types and perform C++ style pointer operations on memory.

Here is an example of using pointers to quickly process an array:

unsafe void Process (int[,] data){
   int length = data.Length;
   fixed (int* b = data){
      int* p = b;
      for (int i = 0; i < length; i++)
          *p++ &= 0xFF;
    }
}

fixed Statement

Within a fixed statement, we can get a pointer to any value type, an array of value types, or a string.

In the case of arrays and strings, the pointer will actually point to the first element, which is a value type.

Value types declared inline within reference types require the reference type to be pinned, as follows:

class Main {//from ww  w . j  a v  a2s  .  c  o  m
   int x;
   static void Main(){
      Test test = new Test();
      unsafe{
         fixed (int* p = &test.x) // Pins test
         {
            *p = 0;
         }
         System.Console.WriteLine (test.x);
      }
   }
}

Pointer-to-Member Operator

In addition to the & and * operators, C# also provides the C++ style -> operator, which can be used on structs:

struct Test{
   int x;
   unsafe static void Main(){
      Test test = new Test();
      Test* p = &test;
      p->x = 1;
      System.Console.WriteLine (test.x);
   }
}

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