Declarations in a for loop

Declarations in a for loop

[Fred Labrosse]

All,

The following doesn't compile (with different messages depending on the
order in which I declare things:

#include <vector>

main()
{
   std::vector<double> doubles;
   double aDouble;

   for (int index = 0,
           std::vector<double>::iterator doublesIter = doubles.begin();
        doublesIter != doubles.end();
        ++doublesIter, ++index)
   {
      if (aDouble == *doublesIter)
         return(index);
   }
}

However, if I declare index and doublesIter before the for, then all
works fine.  Is that a bug?

Fred

Re: Declarations in a for loop

[Eljay Love-Jensen]

Hi Fred,

>However, if I declare index and doublesIter before the for, then all works fine.  Is that a bug?

Nope, not a bug.  What you have here is a case of bad C++ code.

#1
int x, y; // This is good.

#2
int x; std::vector<double>::iterator y; // This is good.

#3
std::vector<double>::iterator x, y; // This is good.

#4
int x, std::vector<double>::iterator y; // This is not good.

You can't put #2 in a for-loop initialization expression (since it's two expressions).

#1 and #3 won't do what you want.

#4 isn't C++, whether inside or outside of a for-loop initialization expression..

HTH,
--Eljay

Re: Declarations in a for loop

[DPalao]

El Miércoles, 18 de Mayo de 2005 17:56, Fred Labrosse escribió:
> All,
>
> The following doesn't compile (with different messages depending on the
> order in which I declare things:
>
> #include <vector>
>
> main()
> {
>    std::vector<double> doubles;
>    double aDouble;
>
>    for (int index = 0,
>            std::vector<double>::iterator doublesIter = doubles.begin();
>         doublesIter != doubles.end();
>         ++doublesIter, ++index)
>    {
>       if (aDouble == *doublesIter)
>          return(index);
>    }
> }
>
> However, if I declare index and doublesIter before the for, then all
> works fine.  Is that a bug?
>
> Fred

As far as I know if you declare several variables in the so-called 
init-statement they have to share the type.

Regards

Re: Declarations in a for loop

[Fred Labrosse]

On Wed, 18 May 2005 18:07:58 +0200
DPalao <dpalao@gmail.com> wrote:
> 
> As far as I know if you declare several variables in the so-called 
> init-statement they have to share the type.

This seems to be the case indeed.

Thanks.

Fred

Re: Declarations in a for loop

[Fred Labrosse]

On Wed, 18 May 2005 11:06:23 -0500
Eljay Love-Jensen <eljay@adobe.com> wrote:

> Hi Fred,
> 
> >However, if I declare index and doublesIter before the for, then all
> >works fine.  Is that a bug?
> 
> Nope, not a bug.  What you have here is a case of bad C++ code.
> 
> #1
> int x, y; // This is good.
> 
> #2
> int x; std::vector<double>::iterator y; // This is good.
> 
> #3
> std::vector<double>::iterator x, y; // This is good.
> 
> #4
> int x, std::vector<double>::iterator y; // This is not good.
> 
> You can't put #2 in a for-loop initialization expression (since it's
> two expressions).
> 
> #1 and #3 won't do what you want.
> 
> #4 isn't C++, whether inside or outside of a for-loop initialization
> expression..

But you can have:

for (int i, int j; ...)

Seen examples of that in Josuttis' OO programming in C++ (while I was
verifying whether I could have several declerations in the for).

Fred