[Mingw-users] Re: 52 Errors with a single map

[Thomas T. <tho...@ya...>]

Joseph McCay wrote:


> >  But based on your error messages, I'll bet you've
> >  mistakenly done
> >  something analogous to one of the following:
> >
> >  Either:
> >
> >  namespace ptl { #include <map> // erroneously
> >  // imports std::map into namespace ptl 
> >  }
> >
> >  or
> > 
> >  namespace ptl { using namespace std; // screws up
> >  // gcc's look-up rules. 
> >  }
>  
 
> My most recent problem was I using the wrong header
> name which was an 
> older version.  I code I gave you compiles fine when
> I use the right 
> header.  The older version had both of those things
> you listed.  What is 
> wrong with both of them?  Are they legal c++?

You should ask this question on comp.c++.moderated,
where you can get a definitive answer.  My
understanding, though, is:

namespace ptl {
#include map
}

causes undefined behavior, because the C++ Standard
Library must be defined in namespace ::std (which is
different from namespace ptl::std).

On the other hand, I'm not sure whether:

namespace ptl { using namespace std; }

is legal or not.  It seems to cause look-up problems
for gcc, in my experience, but I don't know whether
that's because it's undefined behavior or just a bug
in gcc.

The correct way to do it is as follows:

#include <map>
namespace ptl {
    using std::map;
    // Your code here
}

or, if you have to (and you usually don't):

#include <map>
using namespace std;
namespace ptl {
     // Your code here
}

Best regards,

Tom


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