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To: gcc-help@gcc.gnu.org
From: SVisor <svisor@lycos.com>
Subject: Inherited member( void )const - const to be or not to be
Date: Mon, 06 Sep 2004 11:01:00 -0000
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Hi,

If this is wrong list, please point me to a better one.

I have following code. If CONST (as described in code) is defined it 
will not compile (unless I do a C cast to CProvider* in 
CInherited::getProvider(void)const). *I* claim that it should compile 
even if CONST is defined. As the "const" only tells the compiler that 
the function will not change any members of the class, it says nothing 
about the return value. GCC 3.4.1 20040625 wants to see "this" as 
constant in the function.

What is your opinion?

Am I getting myself into trouble with the CInherited class if I use C 
cast (with C++ static/dynamic_cast it fails to compile) to make it compile?

// Jarmo

Following should compile with g++ from command line.
To break it use "-D_CONST":


#include <stdio.h>

// #define _CONST // If defined this will not compile
#ifdef _CONST
#define CONST const
#else
#define CONST
#endif

class CProvider
{
protected:
	const char* str;
public:
	CProvider( const char* s ){ str=s; printf( "CProvider(%s)\n",str );}
	void echo( void ){ printf( "CProvider(%s)::echo( )\n",str ); }
};

class CAbstract
{
public:
	CAbstract( void ){ printf( "CAbstract\n" ); }
	virtual CProvider* getProvider( void )CONST=0;
};

class CAllocated : public CAbstract
{
protected:
	CProvider *ptr;

public:
	CAllocated( void ){ printf( "CAllocated\n" ); ptr=new CProvider( 
"Allocated" ); }

	virtual CProvider* getProvider( void )CONST{ return ptr; }
};

class CInherited : public CAbstract,public CProvider
{
public:
	CInherited( void ):CProvider( "Inherited" ){ printf( "CInherited\n" );  }

	virtual CProvider* getProvider( void )CONST{ return this; }
};

int main( void )
{
	CAllocated tmp1;
	CInherited tmp2;

	tmp1.getProvider( )->echo( );
	tmp2.getProvider( )->echo( );
	
	CAbstract* pTmp1=&tmp1;
	CAbstract* pTmp2=&tmp2;
	pTmp1->getProvider( )->echo( );
	pTmp2->getProvider( )->echo( );
	return 0;
}