using namespace issue

Question

When I use the following

#include <map>

using namespace LCDControl;

Any reference to the std namespace ends up being associated with the LCDControl name space.

For instance:

Generic.h:249: error: 'map' is not a member of 'LCDControl::std'

How do I get around this? I didn't see anything specific to this on any documentation I looked over. Most of them said not to use: using namespace std;.

Here's line 249:

for(std::map<std::string,Widget *>::iterator w = widgets_.begin();

What compiler? Also, do you have anything named map in your LCDControl namespace? Why use using namespace anyway? :) — GManNickG
– GManNickG, Commented Oct 20, 2009 at 1:03
GMan, no 'map is in the LCDControl namespace. I used a namespace because I kept running into names associated with outside header files. For instance, in this case I had something named CHAR, and it conflicted with something somewhere. Instead of renaming it, I dealt with it by wrapping everything inside a namespace. Of course I've never used C++ namespaces before, so here I am. :) — Scott
– Scott, Commented Oct 20, 2009 at 1:05
That's strange, it's behaving as if you forgot to include <map>. Does it work if you use ::std::map instead of std::map? — Tim Sylvester
– Tim Sylvester, Commented Oct 20, 2009 at 1:09
Hmm, seems as if something in LCDControl is hiding std. Is there a using namespace std within the namespace LCDControl { } anywhere? — Tim Sylvester
– Tim Sylvester, Commented Oct 20, 2009 at 1:13
One thing that might cause that is if one of the STL headers is being included somewhere within the LCDControl namespace. e.g., namespace LCDControl { #include <string> }. — Tim Sylvester
– Tim Sylvester, Commented Oct 20, 2009 at 1:15

Tim Sylvester · Accepted Answer · 2009-10-20 01:29:23Z

4

It looks like there's a std namespace within LCDControl that's hiding the global std namespace. Try using ::std::map instead of std::map.

I would say that either there's a using namespace std somewhere within the LCDControl namespace, or possibly there's an #include of a STL header that defines std within the LCDControl namespace.

e.g.:

namespace LCDControl
{
    #include <map>
}

Which would define all the symbols in <map> as part of LCDControl::std, which in turn would hide the global std, or at least any symbols defined in the inner namespace, I'm not sure.

When I tried this under VS2008, I got an error:

namespace testns
{
    int x = 1;
}

namespace hider
{
    namespace testns
    {
        int x = 2;
    }
}

int y = testns::x;
using namespace hider;
int z = testns::x;    // <= error C2872: 'testns' : ambiguous symbol

edited Oct 20, 2009 at 1:29

answered Oct 20, 2009 at 1:19

Tim Sylvester

23.2k2 gold badges82 silver badges99 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Scott Over a year ago

Yeah, I think that's what happened. Here I go 'a searching.

Scott Over a year ago

Yeah that's what it was. Curious that this didn't fix my initial issue. lol... CHAR is still defined multiple times according to the linker. Oh well, at least everything's inside a namespace now.

Ed Swangren · Accepted Answer · 2009-10-20 00:55:47Z

1

The 'map' class lives in the std namespace, so you are going to have to qualify that somewhere. How are you qualifying your map object? You should have no problem doing this:

std::map<foo> myMap;

You can also do something like this if you do not want to explicitly qualify it every time, but also do not want to pollute your global namespace:

using std::map;

answered Oct 20, 2009 at 0:55

Ed Swangren

125k24 gold badges189 silver badges271 bronze badges

2 Comments

Scott Over a year ago

I'm qualifying it with std::map.

Ed Swangren Over a year ago

Yeah, I see that now. Looks like your LCDControl namespace is polluting your global namespace.

Collectives™ on Stack Overflow

using namespace issue

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related