Re: Getting struct fields info at runtime?

"Robert" <>
Fri, 30 Nov 2007 12:27:57 +0100
Thanks for the answer, David and Giovanni, sorry but I forget to explain
clearly that for several reasons the position of the fields is a constrain,
and when I add the new fields to the StructVersion2 I can't add them as the
last fields, but I have to add them in particular position, between two
existing fields, so the use of inheritance is non suitable in this

And also, even if I use inheritance, if in the new StructVersion2 instead of
adding fields I have just to increment the length of a char[] field, if I
try to use an instruction such as this

 StructVersion2(const StructVersion1& s)
     *this = s;

what will be the behaviour of the assignment?
The position of the fields doesn't correspond, so will I get an error?

"David Wilkinson" <> wrote in message

Robert wrote:

Hi all,
I have a situation like this: in my code I have a struct (eg called
StructVersion1) with some fields of several primitive data types (char,
int, ...).
At some point, I have to add some fields in that struct or to increase
the number of chars in one of existings fields, but I have to preserve
the old struct and the new one, so I create a new struct
(StructVersion2): in this way, StructVersion1 and StructVersion2 will
have some fields with the same names (StructVersion2 will always add
fields or increment their length, never remove fields).

If I have an object with some data of StructVersion1 type, is there any
way to copy its fields values in another object of StructVersion2 type,
without manually copying each single field?
Eg, in a .Net application I could use reflection to get the fields info
of both structs at runtime, and execute a cycle that copy each field
value from one object to another.
In a vc++ native project, is there any way to do it, or I have to do it
I tried to give a glance at RTTI, but I didn't understand if that can
help me in any way.

How about this

class StructVersion1
  // StructVersion1 members

struct StructVersion2: StructVersion1
  StructVersion2(const StructVersion1& s)
    *this = s;

  StructVersion2& operator = (const StructVersion1& s)
    StructVersion1& s1 = (StructVersion1&) (*this);
    s1 = s;
    return *this;
  // StructVersion2 members

David Wilkinson
Visual C++ MVP

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