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explanation of c++ typedef line [message #18227]

Thu, 18 September 2008 03:20

captainc
Messages: 278
Registered: December 2006
Location: New Jersey, USA

Experienced Member

Can someone explain to me this line:

typedef tagXYZHANDLE {} * XYZHANDLE;

My interpretation: 'XYZHANDLE is an alias of a pointer to an array of tagXYZHANDLE'? Is this correct?

It's from CodeProject article:
HowTo: Export C++ classes from a DLL
http://lamp.codeproject.com/KB/cpp/howto_export_cpp_classes. aspx

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Re: explanation of c++ typedef line [message #18232 is a reply to message #18227]

Thu, 18 September 2008 11:56

mrjt
Messages: 705
Registered: March 2007
Location: London

Contributor

I don't know, but it doesn't compile. Perhaps an error?

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Re: explanation of c++ typedef line [message #18235 is a reply to message #18227]

Thu, 18 September 2008 14:27

cas_
Messages: 20
Registered: July 2008
Location: Poland

Promising Member

captainc wrote on Thu, 18 September 2008 03:20

My interpretation: 'XYZHANDLE is an alias of a pointer to an array of tagXYZHANDLE'? Is this correct?

No, that would be:

typedef tagXYZHANDLE (*XYZHANDLE)[];

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Re: explanation of c++ typedef line [message #18236 is a reply to message #18235]

Thu, 18 September 2008 15:23

captainc
Messages: 278
Registered: December 2006
Location: New Jersey, USA

Experienced Member

This was one of the comments:

Quote:

typedef void* XYZHANDLE;
typedef void* IJKHANDLE;

is not type safe, since all handle will became mutually replaceable being all void*. (you can assign an XYZ to an IJK).

One way to get around this is to declare a category (empty struct) and point to it.

typedef struct XYZHANDLE_ {} *XYZHANDLE;
typedef struct IJKHANDLE_ {} *IJKHANDLE;

Now IJKHANDLE and XYZHANDLE cannot anymore be assigned each other.

Maybe the author replaced it incorrectly.

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Re: explanation of c++ typedef line [message #18237 is a reply to message #18227]

Thu, 18 September 2008 16:27

mr_ped
Messages: 826
Registered: November 2005
Location: Czech Republic - Praha

Experienced Contributor

There are more uncompilable things:

#include &quot;XyzLibrary.h&quot;
extern &quot;C&quot; XYZAPI IXyz* APIENTRY GetXyz();

(i.e. it's probably problem with quality of the article itself)

That line from first post really looks like missing "struct" keyword, that was also my first idea without reading the article.

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