Using "namespace foo {" instead of explicitly qualifying outside of header files

Question

If a function is declared as such:

namespace foo {
    void bar();
}

Most people define the function like this:

void foo::bar() {
    ...
}

However I like to do it this way:

namespace foo {
    void bar() {
        ...
    }
}

I prefer this style because its saves me from always retyping foo::, which is often tedious in function parameters that accept types declared in that same namespace. Plus its easier to rename the whole namespace.

I'm wondering why I almost never see my style in other peoples code, are there any disadvantages too it, besides the additional indentation level (and you don't even have to indent namespaces)?

`Most people...` really? `I'm wondering why I almost never see my style in other peoples code`, really? — Nawaz, Aug 08 '11 at 15:24
eh? how big is this group of people who's code you've looked at? I rarely see the former... — Nim, Aug 08 '11 at 15:25
I consistently use the same style that you do, with indentation... This seems a fairly subjective question to me. — Matthieu M., Aug 08 '11 at 15:25

score 4 · Accepted Answer · answered Aug 08 '11 at 15:33

4

If you use the foo::bar form, and accidentally define the function with incorrect arguments, you will get a compiler error. If you put the definition in a namespace in the source file, different arguments will simply result in a different function being defined. You won't get an error until you try to link with code which uses your function (which in the case of a DLL, may not be until runtime).

answered Aug 08 '11 at 15:33

James Kanze

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tl;dr: The `foo::bar` form can only be a definition, not declaration. I guess. – Lightness Races in Orbit Aug 08 '11 at 15:52
@Tomalak Yep. The syntax isn't legal for declarations which aren't definitions. – James Kanze Aug 08 '11 at 16:06
"cannot be a non-defining declaration"* then :) – Lightness Races in Orbit Aug 08 '11 at 16:42

score 0 · Answer 2 · answered Aug 08 '11 at 15:26

0

Finding foo::bar on the command-line is not easy. Having foo::bar to grep for is quite nice.

answered Aug 08 '11 at 15:26

murrekatt

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iammilind · Answer 3 · 2011-08-08T15:33:23.867

-2

namespace foo {
    void bar {
        ...
     }
 }

Can cause multiple definition error. This error comes at link time.

Say that you have put this namespace foo in a header file and defined the function bar() inside it. Now, when you include this header file to multiple .cpp file, multiple definitions of foo::bar() will be generated. Thus, linker error.

[Note: I assume that in the 1st case, you are defining foo::bar in a .cpp file.]

edited Aug 08 '11 at 15:33

answered Aug 08 '11 at 15:26

iammilind

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2

Um, really? And the alternative "can" not? – Lightness Races in Orbit Aug 08 '11 at 15:28
@Tomalak, I din't get you. `namespace foo { void bar(); }` will not cause any linker error. Because I assume that `foo::bar()` will be defined in `.cpp` file. – iammilind Aug 08 '11 at 15:32
Why 2 downvotes. What is wrong in the answer. – iammilind Aug 08 '11 at 15:34
And you can assume that the same will be true of `namespace foo { void bar { .. } }`. The "issue" you're talking about has absolutely nothing to do with any difference between the two syntaxes. – Lightness Races in Orbit Aug 08 '11 at 15:46
@Tomalak, OP has asked `I almost never see my style in other peoples code, are there any disadvantages to it`. Forget it. – iammilind Aug 08 '11 at 15:56
Again, what you are talking about is not a disadvantage of that style. It is a disadvantage of defining functions in headers, which you can do just as easily with either syntax. – Lightness Races in Orbit Aug 08 '11 at 16:42

Using "namespace foo {" instead of explicitly qualifying outside of header files

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