INFO: Error C2593 When Archiving an Enumerated Type

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

SUMMARY

In ANSI C, enumerated types are synonyms for "int"; however, in C++, enumerated types are distinct integral types but are not integers themselves. Therefore, if e is an enumerated type and archive is of type CArchive, compiling these statements

   archive << e;
   archive >> e;

   error C2593: 'operator <<' is ambiguous
   error C2593: 'operator >>' is ambiguous

MORE INFORMATION

The following are the prototypes taken from AFX.H. These are the functions that the compiler chooses from when it compiles the statement "archive << e;"

   CArchive& operator<<( BYTE by );
   CArchive& operator<<( WORD w );
   CArchive& operator<<( LONG l );
   CArchive& operator<<( DWORD dw );

   typedef unsigned char    BYTE;   // 8-bit unsigned entity
   typedef unsigned short   WORD;   // 16-bit unsigned number
   typedef long             LONG;   // 32-bit signed number
   typedef unsigned long    DWORD;  // 32-bit unsigned number

   archive << (WORD) e;
   archive >> (WORD&) e;

   -or-

   archive << (unsigned short) e;
   archive >> (unsigned short&) e;

   archive << (int) e;
   archive >> (int&) e;

The following is a complete example demonstrating how to store and load an enumerated type:

Sample Code

   /* Compile options needed: none
   */

   #define _DOS
   #include <afx.h>

   enum DAY
   {
      sunday, monday, tuesday, wednesday, thursday, friday, saturday
   };

   void main( void );

   void main( )
   {
      CFile myFile;

   // Open the file for writing and associate an archive object with it.

      myFile.Open( "testfile", CFile::modeWrite, NULL );
      CArchive archiveOut( &myFile, CArchive::store );

      enum DAY today = tuesday;

   // Use the insertion operator to store the enumerated value
   //    archiveOut << today;
   // will generate an error

      archiveOut << (WORD) today;

      archiveOut.Close();
      myFile.Close();

   // Open the file for reading and associate an archive object with it.

      myFile.Open( "testfile", CFile::modeRead, NULL );
      CArchive archiveIn( &myFile, CArchive::load );

   // Use the extraction operator to load the enumerated value
   // "archiveIn >> today;" would generate an error

      archiveIn >> (WORD&) today;

      archiveIn.Close();
   }