what is problem in (distance) word where declara struct with it ?

Question

1.00/5 (1 vote)

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#include<iostream>
using namespace std;
struct distance
{ int x; };

int main()
{
	distance d1; // what is wrong in this word (distance), compiler say {IntelliSense: "distance" is ambiguous}
				// i thank this is not recerved key word in c++
		return 0;
}

Posted 28-Feb-13 12:03pm

Anderso0on

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2 solutions

Solution 1

Quote:
// i thank this is not recerved key word in c++

Your assumption is right. Hence you have a collision with the STL (with VS 2012 I found distance definition inside the STL's 'xutility internal header'). You may easily verify this either by commenting the using namespace std; or your struct definition (in both cases the ambiguity vanishes).

Posted 28-Feb-13 12:13pm

CPallini

Comments

Sergey Alexandrovich Kryukov 28-Feb-13 20:19pm

5ed, but look how much discussions OP had with me. (I don't really know why didn't I notice your answer 1 hour sooner then mine... :-)
—SA

CPallini 1-Mar-13 3:08am

Thank you.

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-02-28T12:15:00

Solution 2

How could it be a keyword.

Here is how you could sort it out: 1) rename struct distance; 2) put your cared on the old name distance in Visual Studio, use "Go to definition item" of context menu. You will see that declaration. I did it:

C++

template<class _InIt> inline
    typename iterator_traits<_InIt>::difference_type
        __CLRCALL_OR_CDECL distance(_InIt _First, _InIt _Last)
    {   // return distance between iterators
    typename iterator_traits<_InIt>::difference_type _Off = 0;
    _Distance2(_First, _Last, _Off, _Iter_cat(_First));
    return (_Off);
    }

This is from the file xutility; apparently, you got this include via included iostream.

Problem solved. Next time, you will be able to do it by yourself.

—SA

Posted 28-Feb-13 12:15pm

Sergey Alexandrovich Kryukov

Comments

Anderso0on 28-Feb-13 18:32pm

please give me more explain :) , what is xutility file , and what do this code ?

Sergey Alexandrovich Kryukov 28-Feb-13 19:01pm

It just does not matter: this is how Microsoft or any other party implemented iostream internally; nothing else to explain.
You should understand the formal approach: there is an ambiguity in some name; OK, now, let's see what's that name; I've demonstrated how. Just repeat my steps, right now or next time; and you will see how it looks...
—SA

Sergey Alexandrovich Kryukov 28-Feb-13 19:05pm

And, what to do?
How what? remove the clash.

Either 1) remove this include (in this file, I don't see where you need it), 2) remove "using std", and use "std" explicitly where you need it, like std::ifstream, or something; 2) rename your struct::distance. Big deal... :-)

—SA

Anderso0on 28-Feb-13 19:14pm

:) iwanna read about this , are you have any article benfit to me ?

Sergey Alexandrovich Kryukov 28-Feb-13 19:55pm

Yes. Look up any C++ manual on these topics: "include" and "namespaces". They are very simple topics...
—SA

Anderso0on 28-Feb-13 20:03pm

thanks :)

Sergey Alexandrovich Kryukov 28-Feb-13 20:17pm

You are welcome. :-)
I hope you are more or less clear about those issues now and at least know how to sort things out.
I really appreciate that you try to get to essence of things instead of using cookbook recipes.
I hope you can accept the answer formally now (green button) — thanks.
In all cases, your follow-up questions are quite welcome.
—SA

CPallini 1-Mar-13 3:07am

My 5.

Sergey Alexandrovich Kryukov 1-Mar-13 10:41am

Thank you, Carlo.
—SA