static_cast usage

[Gary Labowitz]

Am I doing this correctly? It is a sample program for my class.

#include <iostream>

using namespace std;

int main( )
{
int x=3, y=4;

cout << "using cast ";
cout << static_cast<dou ble> x/y<<endl;

return 0;
}

Compiled with Dev-C++ using minGW compiler I get

parse error before '/' token

on line 10 indicating the static_cast. Changing to (double) runs okay. Is
this a problem with minGW, g++, Dev-C++, me? I have checked archives of all
mailing lists and see nothing there. Compile line is
g++.exe "D:\DPR226\ My Files\Untitled2 .cpp" -o "D:\DPR226\ My
Files\Untitled2 .exe" -l
"D:\Dev-Cpp\include\c++ " -l"D:\Dev-Cpp\include\c++ \mingw32" -l"D:\Dev-Cpp\in
clude" -l"D:\Dev-Cpp\include\c++ \backward" -L"D:\Dev-Cpp\lib"

I don't see it. TIA
--
Gary

[Jerry Coffin]

Re: static_cast usage

In article <F5edncoCwNFE Vh-iU-KYgw@comcast.co m>, glabowitz@comca st.net
says...

[ ... ]
[color=blue]
> cout << static_cast<dou ble> x/y<<endl;[/color]

You have to put the expression being cast into parentheses:

std::cout << static_cast<dou ble>(x)/y << std::endl;

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Phlip]

Re: static_cast usage

> cout << static_cast<dou ble> x/y<<endl;

Try:

cout << static_cast<dou ble> (x)/y<<endl;

However, as a style thing, in this case the static_cast-ed numerator
overwhelms the denominator, making it feel small.

Just use a constructor cast:

cout << double(x) / y <<endl;

I would also not trust the precedence of << over /. Try this:

double xy (double(x) / y);
cout << xy << endl;

--
Phlip

[Rob Williscroft]

Re: static_cast usage

Phlip wrote in news:N2Agb.3347 $lO1.77@newssvr 17.news.prodigy .com:
[color=blue][color=green]
>> cout << static_cast<dou ble> x/y<<endl;[/color]
>
> Try:
>
> cout << static_cast<dou ble> (x)/y<<endl;
>
> However, as a style thing, in this case the static_cast-ed numerator
> overwhelms the denominator, making it feel small.
>
> Just use a constructor cast:
>
> cout << double(x) / y <<endl;[/color]

Assuming you don't have a broken optimizer you can also go "cast free".

cout << (x * 1.0 / y) << endl;

Rob.
--

http://www.victim-prime.dsl.pipex.com/

[Gary Labowitz]

Re: static_cast usage

"Rob Williscroft" <rtw@freenet.RE MOVE.co.uk> wrote in message
news:Xns940D9F8 0AECF6ukcoREMOV Efreenetrtw@195 .129.110.204...[color=blue]
> Phlip wrote in news:N2Agb.3347 $lO1.77@newssvr 17.news.prodigy .com:
>[color=green][color=darkred]
> >> cout << static_cast<dou ble> x/y<<endl;[/color]
> >
> > Try:
> >
> > cout << static_cast<dou ble> (x)/y<<endl;
> >
> > However, as a style thing, in this case the static_cast-ed numerator
> > overwhelms the denominator, making it feel small.
> >
> > Just use a constructor cast:
> >
> > cout << double(x) / y <<endl;[/color]
>
> Assuming you don't have a broken optimizer you can also go "cast free".
>
> cout << (x * 1.0 / y) << endl;[/color]

Egad, I'm an idiot. So static_cast requires the expression to be in
parentheses, eh?
Thanks for all the answers, they are very creative. Of the lot, I think I
prefer static_cast<dou ble>(x) best since it seems more in line with C++
using static_cast.
I did use (double)x and the 1.0 multiplier as well, but they avoid the
issue.

This raises another issue: do you really prefer double(x) to (double)x?
[Phlip] It does follow the structure of the static_cast form.

No wonder the archives search didn't find anything!
--
Gary

[Christian Brechbühler]

Re: static_cast usage

Gary Labowitz wrote:[color=blue]
> This raises another issue: do you really prefer double(x) to (double)x?[/color]

Absolutely. The latter is a C-style cast and I avoid it. In my
opinion, double(x) expresses the conversion most clearly -- unless your
assignment explicitly asked you to use a static cast.

Christian

[Gary Labowitz]

Re: static_cast usage

"Christian Brechbühler" <c_brechbuehler @yhaoo.com> wrote in message
news:7XJgb.7074 41$uu5.116817@s ccrnsc04...[color=blue]
> Gary Labowitz wrote:[color=green]
> > This raises another issue: do you really prefer double(x) to (double)x?[/color]
>
> Absolutely. The latter is a C-style cast and I avoid it. In my
> opinion, double(x) expresses the conversion most clearly -- unless your
> assignment explicitly asked you to use a static cast.[/color]

Oh, oh. I hate to admit it on this one, but I'm the teacher!
I ask them to use static cast.
--
Gary

[Phlip]

Re: static_cast usage

> > > cout << static_cast<dou ble> (x)/y<<endl;
[color=blue]
> No wonder the archives search didn't find anything![/color]

That right there is a canonical reason to use elaborate_cast. You can
search for it in your code.

(Another reason is they generally constrain their argument types such
that attempts to change the cast into what a () C style cast would
recognize as a different kind of elaborate_cast cause an error.)

--
Phlip