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-> operator

 
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gordon111



Joined: 05 Jul 2007
Posts: 18

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-> operator
PostPosted: Wed Aug 22, 2007 3:05 pm     Reply with quote
Can anyone please give me a hint as what this operator (->) does...for example.

Code:

   if(cb->buf[0] == readDips())         // Valid Address
      {
         switch(cb->buf[1])               // Function
         {
            case 0x01:   // Read Coil Status
             {
               readCoils();                        // Read status of Coils
               
               break;
            }
ckielstra



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

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PostPosted: Wed Aug 22, 2007 3:53 pm     Reply with quote
http://www.amazon.com/C-Programming-Language-2nd/dp/0131103628

The arrow notation is used when dereferencing a pointer to a structure. On function calling it is often more efficient to pass a pointer to a structure than passing (a copy of) the structure.

To dereference the structure you could write code like
Code:
(*cb).buf[1]
Note, the parentheses are necessary here because the . operator has higher precedence than the indirection operator, *. We must first dereference the pointer, and then select its appropriate member.

Since dereferencing structures like this is a common task they have defined a special pointer operator, called arrow, and the above code becomes:
Code:
cb->buf[1]
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