[c++] 'using namespace std;' Good practice?

If you declare using namespace XYZ; at the top of a file, then all symbols within that namespace are "imported". This isn''t a problem in a closed compilation unit (source file), but if the file will be introduced to other compilation units (header file), then it''s just plain wrong. In summary, use fully qualified object names in headers, and feel free to introduce the entire namespace into source files, but beware the potential for collisions (which will be resolved by full qualification). It makes no sense to introduce two namespaces and then have them generate collisions.

I suggest to use "using namespace std;" ONLY under .CPP.
For .H, it is better to have this:

class MyClass
{
  ...
public:
  std::string & GetName() const { return _name; }
  ...
private:
  std::string _name;
};
 

Oluseyi''s right, you should not write ''using namespace std'' in a header file (unless you''re the sole manager of your project and you don''t want anyone else to ever use your headers). However, here''s something I just thought of and I don''t know if it''s right or wrong, I''m just throwing the idea:

namespace A{
using namespace std;

//Code can use std
};

//Code has to specify std::

This code could be put in a header file without ''polluting'' the translation unit with std::. However, it has the consequence that if someone writes ''using namespace A'', it also includes all of std. If there''s a warning about it, I would say that it''s OK.

Cédric

Yep that makes sence. I was new and probably was using namespaces right there in the header and when warned off decided not to declare namespace use at call doing all calls the long way.

Thanks all.

Chris Brodie
http:\\fourth.flipcode.com