checking cast from void*

**manustone** · 07-14-2009

Hi
today I mistaped a cast from void* to the wrong type
and everything was fine.
How can I check/realize that I am using the wrong class
or prevent cases like the one below?

Code:

void main()
{

    void *ptr;
    MyObject2* p2 = &obj2;
    ptr = p2;

    // here I casted to MyObject1 a pointer to
    // MyObject2...
    MyObject1* p1 = static_cast< MyObject1* >( ptr );

   // ...and he works fine! It writes 20: 
   // how to prevent this?
    p1->Mutator1( 20 );

}

class MyObject1
{
public:
    void Mutator1( int a )
    {
        std::cout << a << std::endl;
     }
};

class MyObject2
{
public:
    void Mutator2( int a )
    {
        std::cout << a << std::endl;
        }
};

**tabstop** · 07-14-2009

I think dynamic_cast checks that it makes sense.

**laserlight** · 07-14-2009

Originally Posted by manustone

today I mistaped a cast from void* to the wrong type
and everything was fine.
How can I check/realize that I am using the wrong class
or prevent cases like the one below?

Don't involve a pointer to void in the first place.

Originally Posted by tabstop

I think dynamic_cast checks that it makes sense.

dynamic_cast would only make sense where polymorphic types are involved.

**tabstop** · 07-14-2009

Originally Posted by laserlight

Don't involve a pointer to void in the first place.

dynamic_cast would only make sense where polymorphic types are involved.

IAW the first sentence.

And I ended up checking the dynamic_cast -- apparently you can't dynamic_cast void* to anything at all (compile error), so that's a washout.

**cpjust** · 07-14-2009

IAW??

**tabstop** · 07-14-2009

Originally Posted by cpjust

IAW??

I don't know. Do you agree with the first sentence?

**bithub** · 07-14-2009

I think he's wondering (as I am) what IAW means.

**anon** · 07-15-2009

When you use a void* then it already means "I don't want no stinking compiler helping me about getting my types right. I know better".

So you can't keep using void* and expect help from the compiler.

You could describe why you are using a void* in the first place because one should be needed quite rarely in C++ programs.

**phantomotap** · 07-15-2009

"I Agree With"

Soma

**Elysia** · 07-15-2009

Since no one has mentioned void main yet...
SourceForge.net: Void main - cpwiki

Also, to use functions that accepts any types, take a look at polymorphism and templates. No need for void*.

**manustone** · 07-16-2009

Hi guys!
First of all I wish to thanks everyone for their reply.
I used void* becasue for me means somekind of everything
( last post got the right point )!
After my post, few days ago I found a very interesting class in boost library called boost::any and boost::any_cast.
Pleae, have a look to it; it is a container for everything that has a copy-constructor ( I hope to rember right ).
Have a nice day!
ManuStone

Code:

void CastToRightType( boost::any& obj )
{
       MyObject1* pnt = boost::any_cast<  MyObject1* >( obj );
}
void main()
{
    MyObject2 obj2;
    MyObjec2 obj1;
    boost::any anyObject1 = &obj1;
    boost::any anyObject2 = &obj2;

   CastToRightType( anyObject1 );    // fine
   CastToRightType( anyObject2 )     // exception
}

**Elysia** · 07-16-2009

Change your void main and read up about templates.

Code:

template<typename T> void CastToRightType( T& obj )
{
       
}

// Use int main FFS
int main()
{
    MyObject2 obj2;
    MyObjec2 obj1;

   CastToRightType( obj1 );    // fine
   CastToRightType( obj2 );    // fine
}

**CornedBee** · 07-16-2009

The implementation of Boost.Any is pretty simple, compared to other Boost libraries. You could simply look at its code.

Thread: checking cast from void*

Thread Tools

Search Thread

Display

checking cast from void*

Similar Threads

Profiler Valgrind

Including The Right DLLs

How to fix misaligned assignment statements in the source code?

Problems about gcc installation

errors in class(urgent )