What is a handle in C

Question

I have been told that a handle is sort of a pointer  but not  and that it allows you to keep a reference to an object  rather than the object itself  What is a more elaborate explanation

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In C   CLI  a handle is a pointer to an object located on the GC heap  Creating an object on the  unmanaged  C   heap is achieved using new and the result of a new expression is a  normal  pointer  A managed object is allocated on the GC  managed  heap with a gcnew expression  The result will be a handle  You can t do pointer arithmetic on handles  You don t free handles  The GC will take care of them  Also  the GC is free to relocate objects on the managed heap and update the handles to point to the new locations while the program is running

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HANDLE hnd  is the same as void   ptr   HANDLE is a typedef defined in the winnt h file in Visual Studio  Windows    typedef void  HANDLE    Read more about HANDLE

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This appears in the context of the Handle-Body-Idiom  also called Pimpl idiom  It allows one to keep the ABI  binary interface  of a library the same  by keeping actual data into another class object  which is merely referenced by a pointer held in an  handle  object  consisting of functions that delegate to that class  Body     It s also useful to enable constant time and exception safe swap of two objects  For this  merely the pointer pointing to the body object has to be swapped

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A handle is a sort of pointer in that it is typically a way of referencing some entity   It would be more accurate to say that a pointer is one type of handle  but not all handles are pointers   For example  a handle may also be some index into an in memory table  which corresponds to an entry that itself contains a pointer to some object   The key thing is that when you have a  handle   you neither know nor care how that handle actually ends up identifying the thing that it identifies  all you need to know is that it does   It should also be obvious that there is no single answer to  what exactly is a handle   because handles to different things  even in the same system  may be implemented in different ways  under the hood    But you shouldn t need to be concerned with those differences

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A handle is whatever you want it to be   A handle can be a unsigned integer used in some lookup table   A handle can be a pointer to  or into  a larger set of data   It depends on how the code that uses the handle behaves  That determines the handle type   The reason the term  handle  is used is what is important  That indicates them as an identification or access type of object  Meaning  to the programmer  they represent a  key  or access to something

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A handle is a pointer or index with no visible type attached to it  Usually you see something like    typedef void  HANDLE   HANDLE myHandleToSomething   CreateSomething      So in your code you just pass HANDLE around as an opaque value   In the code that uses the object  it casts the pointer to a real structure type and uses it    int doSomething HANDLE s  int a  int b         Something  something   reinterpret cast lt Something  gt  s        return something- gt doit a  b        Or it uses it as an index to an array vector    int doSomething HANDLE s  int a  int b         int index    int s       try            Something amp  something   vecSomething index            return something doit a  b          catch  boundscheck amp  e             throw SomethingException INVALID HANDLE

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A handle can be anything from an integer index to a pointer to a resource in kernel space  The idea is that they provide an abstraction of a resource  so you don t need to know much about the resource itself to use it   For instance  the HWND in the Win32 API is a handle for a Window  By itself it s useless  you can t glean any information from it  But pass it to the right API functions  and you can perform a wealth of different tricks with it  Internally you can think of the HWND as just an index into the GUI s table of windows  which may not necessarily be how it s implemented  but it makes the magic make sense    EDIT  Not 100  certain what specifically you were asking in your question  This is mainly talking about pure C C

[c++] What is a handle in C++?

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