When writing C++ member definitions, is there any reason to prefer putting them inside a namespace block over fully qualifying them, or vice versa?

Question

In a C++ class, we can write our members in either of two styles. We can put them inside of a namespace block, or we can fully qualify each.

Is there any reason to prefer one style over the other?

Header file looks like this (bar.h):

namespace foo
{
    class Bar
    {
    public:
        Bar();
        int Beans();
    };
}

Style 1 (bar.cpp) - Declarations within namespace block:

#include "bar.h"
namespace foo
{
    Bar::Bar()
    {
    }

    int Bar::Beans()
    {
    }
}

Style 2 (bar.cpp) - Fully qualified declarations:

#include "bar.h"

foo::Bar::Bar()
{
}

int foo::Bar::Beans()
{
}

So my question, again, is: is there any reason to prefer one style over the other?

Personal preference, another level of indentation, more/less typing... Nothing technical though. — Seth Carnegie, May 22 '12 at 01:05
@dirkgently, that question seems similar at first glance, but is actually quite different. — Boinst, May 22 '12 at 01:09
[this one](http://stackoverflow.com/q/6984444/385094) on the other hand is very similar. — Boinst, May 22 '12 at 01:12

score 0 · Answer 1 · edited May 23 '17 at 12:11

Here's a possible answer that was posted by James Kanze in answer to another similar question. (edit: note from the comment thread, this only applies to non-member functions).

Prefer the fully qualified form (style 2).

Functions written in this style are explicitly a definition, not a declaration.

That is to say, using Style 2, if you accidentally define a function with incorrect arguments, you'll get a compiler error alerting you to that fact.

Using Style 1, if you define a function with incorrect arguments it will define a different function. It will compile fine, but you'll get a linker error explaining that the method is not defined. This will probably be harder to diagnose than the compiler error resulting from Style 2.

That only applies to non-member functions. If you try to define a member function with the wrong arguments using style #1 _or_ style #2 you will most definitely get a compiler error. — Seth Carnegie, May 22 '12 at 01:23

When writing C++ member definitions, is there any reason to prefer putting them inside a namespace block over fully qualifying them, or vice versa?

1 Answers1