Just what is an IntPtr exactly

Question

Through using IntelliSense and looking at other people s code  I have come across this IntPtr type  every time it has needed to be used I have simply put null or IntPtr Zero and found most functions to work  What exactly is it and when why is it used

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A direct interpretation  An IntPtr is an integer which is the same size as a pointer   You can use IntPtr to store a pointer value in a non-pointer type   This feature is important in  NET since using pointers is highly error prone and therefore illegal in most contexts   By allowing the pointer value to be stored in a  safe  data type  plumbing between unsafe code segments may be implemented in safer high-level code -- or even in a  NET language that doesn t directly support pointers   The size of IntPtr is platform-specific  but this detail rarely needs to be considered  since the system will automatically use the correct size   The name  IntPtr  is confusing -- something like Handle might have been more appropriate   My initial guess was that  IntPtr  was a pointer to an integer   The MSDN documentation of IntPtr goes into somewhat cryptic detail without ever providing much insight about the meaning of the name   An alternative perspective  An IntPtr is a pointer with two limitations    It cannot be directly dereferenced It doesn t know the type of the data that it points to    In other words  an IntPtr is just like a void  -- but with the extra feature that it can  but shouldn t  be used for basic pointer arithmetic   In order to dereference an IntPtr  you can either cast it to a true pointer  an operation which can only be performed in  unsafe  contexts  or you can pass it to a helper routine such as those provided by the InteropServices Marshal class  Using the Marshal class gives the illusion of safety since it doesn t require you to be in an explicit  unsafe  context  However  it doesn t remove the risk of crashing which is inherent in using pointers

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Here s an example  I m writing a C  program that interfaces with a high-speed camera  The camera has its own driver that acquires images and loads them into the computer s memory for me automatically  So when I m ready to bring the latest image into my program to work with  the camera driver provides me with an IntPtr to where the image is ALREADY stored in physical memory  so I don t have to waste time resources creating another block of memory to store an image that s in memory already  The IntPtr just shows me where the image already is

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What is a Pointer   In all languages  a pointer is a type of variable that stores a memory address  and you can either ask them to tell you the address they are pointing at or the value at the address they are pointing at   A pointer can be thought of as a sort-of book mark  Except  instead of being used to jump quickly to a page in a book  a pointer is used to keep track of or map blocks of memory   Imagine your program s memory precisely like one big array of 65535 bytes   Pointers point obediently  Pointers remember one memory address each  and therefore they each point to a single address in memory    As a group  pointers remember and recall memory addresses  obeying your every command ad nauseum    You are their king   Pointers in C      Specifically in C   a pointer is an integer variable that stores a memory address between 0 and 65534    Also specific to C   pointers are of type int and therefore signed    You can t use negatively numbered addresses though  neither can you access an address above 65534  Any attempt to do so will throw a System AccessViolationException   A pointer called MyPointer is declared like so      int  MyPointer    A pointer in C  is an int  but memory addresses in C  begin at 0 and extend as far as 65534   Pointy things should be handled with extra special care  The word unsafe is intended to scare you  and for a very good reason  Pointers are pointy things  and pointy things e g  swords  axes  pointers  etc  should be handled with extra special care   Pointers give the programmer tight control of a system  Therefore mistakes made are likely to have more serious consequences   In order to use pointers  unsafe code has to be enabled in your program s properties  and pointers have to be used exclusively in methods or blocks marked as unsafe   Example of an unsafe block  unsafe          Place code carefully and responsibly here       How to use Pointers  When variables or objects are declared or instantiated  they are stored in memory    Declare a pointer by using the   symbol prefix     int  MyPointer    To get the address of a variable  you use the  amp  symbol prefix     MyPointer    amp MyVariable   Once an address is assigned to a pointer  the following applies    Without   prefix to refer to the memory address being pointed to as an int     MyPointer    amp MyVariable     Set MyPointer to point at MyVariable   With   prefix to get the value stored at the memory address being pointed to     MyPointer is pointing at      MyPointer   Since a pointer is a variable that holds a memory address  this memory address can be stored in a pointer variable   Example of pointers being used carefully and responsibly      public unsafe void PointerTest                 int x   100     Create a variable named x          int  MyPointer    amp x     Store the address of variable named x into the pointer named MyPointer          textBox1 Text     int MyPointer  ToString       Displays the memory address stored in pointer named MyPointer          textBox2 Text     MyPointer  ToString       Displays the value of the variable named x via the pointer named MyPointer           Notice the type of the pointer is an int  This is because C  interprets memory addresses as integer numbers  int    Why is it int instead of uint    There is no good reason   Why use pointers   Pointers are a lot of fun  With so much of the computer being controlled by memory  pointers empower a programmer with more control of their program s memory   Memory monitoring   Use pointers to read blocks of memory and monitor how the values being pointed at change over time   Change these values responsibly and keep track of how your changes affect your computer

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Well this is the MSDN page that deals with IntPtr  The first line reads   A platform-specific type that is used to represent a pointer or a handle   As to what a pointer or handle is the page goes on to state   The IntPtr type can be used by languages that support pointers  and as a common means of referring to data between languages that do and do not support pointers  IntPtr objects can also be used to hold handles  For example  instances of IntPtr are used extensively in the System IO FileStream class to hold file handles   A pointer is a reference to an area of memory that holds some data you are interested in  A handle can be an identifier for an object and is passed between methods classes when both sides need to access that object

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MSDN tells us      The IntPtr type is designed to be an   integer whose size is   platform-specific  That is  an   instance of this type is expected to   be 32-bits on 32-bit hardware and   operating systems  and 64-bits on   64-bit hardware and operating systems       The IntPtr type can be used by   languages that support pointers  and   as a common means of referring to data   between languages that do and do not   support pointers       IntPtr objects can also be used to   hold handles  For example  instances   of IntPtr are used extensively in the   System IO FileStream class to hold   file handles       The IntPtr type is CLS-compliant    while the UIntPtr type is not  Only   the IntPtr type is used in the common   language runtime  The UIntPtr type is   provided mostly to maintain   architectural symmetry with the IntPtr   type    http   msdn microsoft com en-us library system intptr VS 71  aspx

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It s a  native  platform-specific  size integer   It s internally represented as void  but exposed as an integer  You can use it whenever you need to store an unmanaged pointer and don t want to use unsafe code  IntPtr Zero is effectively NULL  a null pointer

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It s a value type large enough to store a memory address as used in native or unsafe code  but not directly usable as a memory address in safe managed code   You can use IntPtr Size to find out whether you re running in a 32-bit or 64-bit process  as it will be 4 or 8 bytes respectively

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An IntPtr is a value type that is primarily used to hold memory addresses or handles  A pointer is a memory address  A pointer can be typed  e g  int   or untyped  e g  void    A Windows handle is a value that is usually the same size  or smaller  than a memory address and represents a system resource  like a file or window

[c#] Just what is an IntPtr exactly?

A direct interpretation

An alternative perspective

Examples related to c#

Examples related to intptr