Re: std::count leaked outside namespace std?

[James Dennett]

On Wed, Apr 24, 2013 at 5:25 AM, Nathan Ridge  wrote:
>> Here's a simple program:
>>
>> #include 
>> #include 
>>
>> int main()
>> {
>> std::vector vec;
>> count(vec.begin(), vec.end(), 0); // shouldn't this be std::count ?
>> }
>>
>> The above compiles successfully, but I think it shouldn't. I expect a
>> message like "error: `count` not declared in scope" because I meant to
>> say std::count. Isn't this a bug, or am I missing something?
>
> It is not a bug. std::count is being found by argument-dependent lookup [1].
>
> Regards,
> Nate
>
> [1] http://en.wikipedia.org/wiki/Argument-dependent_name_lookup

For completeness (or something closer to it): the code is
non-portable, as the C++ Standard doesn't say in which namespace the
type named by std::vector::iterator is defined.  It's commonly
either (a) in namespace std, in which case the code above compiles, or
(b) a raw pointer, in which case the code above does not compile.
It's also entirely possible that switching from a debug build to a
non-debug one might change from (a) to (b) with the same compiler and
library.

-- James

RE: std::count leaked outside namespace std?

[Nathan Ridge]

> Here's a simple program:
>
> #include 
> #include 
>
> int main()
> {
> std::vector vec;
> count(vec.begin(), vec.end(), 0); // shouldn't this be std::count ?
> }
>
> The above compiles successfully, but I think it shouldn't. I expect a
> message like "error: `count` not declared in scope" because I meant to
> say std::count. Isn't this a bug, or am I missing something?

It is not a bug. std::count is being found by argument-dependent lookup [1].

Regards,
Nate

[1] http://en.wikipedia.org/wiki/Argument-dependent_name_lookup 
  

Re: std::count leaked outside namespace std?

[bd satish]

Thanks Paolo, ADL is news to me.


On 24 April 2013 01:43, Paolo Carlini  wrote:
> You are: https://en.wikipedia.org/wiki/Argument-dependent_name_lookup
>
> Paolo.
>

Re: std::count leaked outside namespace std?

[Paolo Carlini]

On 04/23/2013 11:26 PM, bd satish wrote:

Hi,

Here's a simple program:

#include 
#include 

int main()
{
   std::vector  vec;
   count(vec.begin(), vec.end(), 0);   // shouldn't this be std::count ?
}

The above compiles successfully, but I think it shouldn't. I expect a
message like "error: `count` not declared in scope" because I meant to
say std::count. Isn't this a bug, or am I missing something?

You are: https://en.wikipedia.org/wiki/Argument-dependent_name_lookup

Paolo.