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how to sub-class an AnsiString

Posted on 2014-02-05
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Last Modified: 2014-02-05
I wish to derive a class from an AnsiString in BCB5 or Embarcadero EX2. my attempt results in the compiler error :
[BCC32 Error] Unit2.h(25): E2049 Class type 'TTaggedString' cannot be marked as __declspec(delphireturn)
  Full parser context
    Unit2.h(19): class TTaggedStringCan this be done ?

my code is as follows:
//header file
class TTaggedString : public AnsiString
{
      public:
    int tag;
    TTaggedString();
    ~TTaggedString();
};
//.cpp file

TTaggedString::TTaggedString() : AnsiString()
{
      tag = 0; //default
}
//---------------------------------------------------------------------------
TTaggedString::~TTaggedString()
{
}
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Question by:alcindor
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Expert Comment

by:rawinnlnx9
ID: 39835954
class TTaggedString : AnsiString

Drop the public from the AnsiString. It inherits the scope of it's parent.
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Author Comment

by:alcindor
ID: 39835991
I tried that on BCB5 and XE2 compilers and the same error is given.
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Expert Comment

by:rawinnlnx9
ID: 39835995
Oh! Hmm... I'll fire up C++ and give this a run.
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Accepted Solution

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jkr earned 500 total points
ID: 39836773
I'm afraid to state it seems you can't - for a reason as simple as it is important. See http://docwiki.embarcadero.com/RADStudio/XE5/en/The_declspec_Keyword_Extension 


 __declspec(delphireturn)

The delphireturn argument is for internal use only by the VCL in C++Builder. It is used for declarations of classes that were created in C++Builder to support Object Pascal built-in data types and language constructs, because they do not have a native C++ type. These include Currency, UnicodeString, AnsiString, Variant, TDateTime, and Set. The delphireturn argument marks C++ classes for VCL-compatible handling in function calls as parameters and return values. This modifier is needed when passing a structure by value to a function between Object Pascal and C++.

If you are trying to inherit from a class that has member which do not represent a native C++ type, it can't work.
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Author Closing Comment

by:alcindor
ID: 39836830
Thanks for your help.
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