static_cast<int>(b)=a+1 problem

hello all group members
sir i have pick the tutorial for some previous months from this bullet in board site
but their is some problem
<code>
#include<iostream.h>
int main(int argc,char *argv[])
{
int a=15;
const int b=a;
static_cast<int>(b)=a+1; //here is showing the problem like lvalue
// something like this
cout<<b<<endl;
return 0;
}
</code>
please solve this problem
from
deepak

[AssKoala]

static_cast<TYPE>(VAR), const_cast<>(), etc all return rvalues. That code shouldn't work.

Oddly, though, Visual Studio 2005 doesn't seem to care but g++ 3.4.2 sure does. Visual Studio (seems to) just removes the "const" qualifier from b.

In C++, you aren't supposed to be able to edit a const anyways. That's a C-ism (and it's always great to muck with your const variables).

Now, there are other errors in that code:
- it should be #include <iostream>
- you need to use "std::cout" and "std::endl" or add "using namespace std;". Personally, I prefer the former.

Originally Posted by AssKoala

static_cast<TYPE>(VAR), const_cast<>(), etc all return rvalues. That code shouldn't work.

Oddly, though, Visual Studio 2005 doesn't seem to care but g++ 3.4.2 sure does. Visual Studio (seems to) just removes the "const" qualifier from b.

In C++, you aren't supposed to be able to edit a const anyways. That's a C-ism (and it's always great to muck with your const variables).

Now, there are other errors in that code:
- it should be #include <iostream>
- you need to use "std::cout" and "std::endl" or add "using namespace std;". Personally, I prefer the former.

================================================== ======
u said i have to use using namespace std
but i have used it already
the main problem of static cast
plz send me the code which use static cast

[teknomage1]

He's sayng don't try to assign to a variable declared const.

[Valmont]

A static_cast is not to cast away constants. The code you presented does not meet the ISO C++ standards.

You'll need the const_cast keyword. This keyword is the only keyword allowed to cast away constness, explicitly stated by the ISO commitee.

Here is the code you're looking for:

#include <iostream>

using namespace std;

int main()
{
	int a = 15;
	const int b = a;

	const_cast<int&> (b)=a+1; //OK

	cout<<b<<endl; //Output is 16.
	cout<<a<<endl; //Output is 15.

	return 0;
}

In C++, you aren't supposed to be able to edit a const anyways.

The ISO requirements lets you cast away constness. One has to be carefull though, but that's a different topic.

In general, this is a (any) cast:
"I know what I am doing so Mr. Compiler, please be quiet."

[kyoryu]

Originally Posted by Valmont

The ISO requirements lets you cast away constness. One has to be carefull though, but that's a different topic.

That's an understatement. If you're using const_cast, you should know VERY well what you're doing, and why you're doing it. Const variables are usually const for a reason, and you can break all sorts of neat things by working around const-ness.

And I'd say it's on topic. Sometimes the proper answer to "how do I do X?" is "unless you *really* know what you're doing, don't." And this is one of those cases.

Originally Posted by Valmont

In general, this is a (any) cast:
"I know what I am doing so Mr. Compiler, please be quiet."

Well, except for a dynamic_cast, which is more like "Hey, is it okay if I do this?" And that *is* off-topic

[Valmont]

Nevertheless, the OP asked how to cast away a const. So post the code if you'd like to help within the ISO specifications.