E2238 Multiple declaration for 'identifier' (C++)

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An identifier was improperly declared more than once.

This error might be caused by conflicting declarations, such as:

• int a; double a;
• A function declared in two different ways
• A label repeated in the same function
• Some declaration repeated, other than an extern function or a simple variable

Conflicting declarations can also happen by inadvertently including the same header file twice. For example, given:

 //a.h
 struct A { int a; };
 //b.h
 #include "a.h"
 //myprog.cpp
 #include "a.h"
 #include "b.h"

myprog.cpp will get two declarations for the struct A. To protect against this, one would write the a.h header file as:

 //a.h
 #ifndef __A_H
 #define __A_H
 struct A { int a; };
 #endif

This will allow one to safely include a.h several times in the same source code file.

Example Using RTL Headers and OS X Headers

In a multi-device application compiled for the OS X target platform, E2238 can occur because the OS X headers "iodbcunix.h" and "sqltypes.h" declare typedefs for DWORD and ULONG, and the C++Builder sysmac.h, which is included by System.hpp, also provides similar typedefs.

[bccosx Error] iodbcunix.h(128): E2238 Multiple declaration for 'DWORD'
  Full parser context
    Unit1.cpp(10): #include c:\program files (x86)\embarcadero\studio\16.0\include\osx\crtl\iodbcunix.h
[bccosx Error] sysmac.h(1279): E2344 Earlier declaration of 'DWORD'
  Full parser context
    Unit1.cpp(10): #include c:\program files (x86)\embarcadero\studio\16.0\include\osx\crtl\iodbcunix.h

If you must include "iodbcunix.h" and "sqltypes.h" in a translation unit that also uses the System.hpp header, use the following approach:

#include <iodbcunix.h> // Include the OSX headers first
#include <sqltypes.h>  // Include the OSX headers first 
 
#define _DWORD_DEFINED // Define the _DWORD_DEFINED macro to prevent a new declaration of DWORD
#define _ULONG_DEFINED // Define the _ULONG_DEFINED macro to prevent a new declaration of ULONG
#include <System.hpp>

You can also specify these two macros in the local options of the affected source file:

1. In the Project Manager, right-click the source file that contains the #include <iodbcunix.h> and #include <sqltypes.h>.
2. From the context menu, select Edit local options.
3. On the C++ (Shared Options) page, click the ellipsis [...] in the Conditional Defines field.
4. On the Conditional Defines dialog box, add the following entries in the entry field:

   _DWORD_DEFINED; _ULONG_DEFINED

5. Click Add.
6. Click OK.