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Union of pointer

 
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Franck26



Joined: 29 Dec 2007
Posts: 122
Location: Ireland

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Union of pointer
PostPosted: Fri Mar 14, 2008 11:18 am     Reply with quote

Hello,
I'm trying to use an union of pointer and I'm very not successful...

Code:
union uPointer
{
   unsigned int8* ptr1;
   unsigned int8* ptr2;
};

void MainProg()
{

   union uPointer uptr;
   unsigned int8 Var1;
   unsigned int8 Var2;
   
   Var1 = 0;
   Var2 = 0;
   
   uptr.ptr1 = &Var1;
   uptr.ptr2 = &Var2;
   
}


I thought that uptr.ptr1 would point on Var1 and uptr.ptr2 on Var2.
But the result is that both of the pointer are on Var2...

Do you have an idea about that?

Thanks for any help.
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Fri Mar 14, 2008 11:22 am     Reply with quote

In a union all members are overlayed, i.e. they all share the same memory bytes. When you assigned Var2 the other value was overwritten. From your question it looks like you want to use a structure instead. Change you program by replacing 'union' by the word 'struct'.
Franck26



Joined: 29 Dec 2007
Posts: 122
Location: Ireland

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PostPosted: Fri Mar 14, 2008 11:32 am     Reply with quote

Thanks for your answer ckielstra,
You're right, it works fine with a structure
Embarassed

Franck,
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