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Struct member offsets

Started by Tispe Mar 28, 2012 at 11:54 AM 1 replies 1k views

Original Post

Mar 28, 2012 at 11:54 AM

Hi

Say you have a char pointer "p" to an array of characters. Now p+1 would give you the second character and so on.

The same applies for structs. If a struct is 40 Bytes long, then structobject+1 increments by 40 bytes.

How does this applies to members of a struct?


 struct MyStruct
 {
 int no;
 int idx_x,idx_y,idx_z;
 float tx,ty,tz,tw;
 };
 
 
 MyStruct &pData = ArrayOfMyStructs[47];
 int offset = 3;
 pData.no+offset; //Where is this address?

Does pData.no+offset; refer to ArrayOfMyStructs[50].no, or does it refer to ArrayOfMyStructs[47].idx_z?

Brother Bob

Mar 28, 2012 at 12:06 PM

When pData is a pointer, then pData.no is not valid syntax to begin with. But even if you meant pData->no, then pData->no+3 simply means the value of the no-member plus three.

If, on the other hand, you meant (&pData->no)+3, then that is equivalent to int *pNo=(&pData->no); pNo+3 which moves an int-pointer three steps forwards. In practice, that would mean it likely points to ArrayOfMyStructs[47].idx_z.

Tispe

Mar 28, 2012 at 12:10 PM

Thank you

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