way to separate non-class library into header and implementation

Let's say there is a library named test, the header "test.hpp" is like follows:

namespace test
{
int myfun(int a);
}


And as for the implementaion, which style is better?

#include"test.hpp"
int test::myfun(int a){
return a*a;
}


or

#include"test.hpp"
namespace test
{
int myfun(int a){
return a*a;
}
}


1 Answer
1

Suppose you have multiple namespaces or nested namespaces in your header as :

namespace test{
namespace subtest{
int Foo(int);
//many other functions go here
} //namespace subtest
} //namespace test


And

namespace test1{
int Foo(int);
}
namespace test2{
int Bar(int);
}


In these cases you should always go with Second implementation as it makes your code more readable and easy to debug.

First one :

#include "test.hpp"
int test::subtest::Foo(int x){return x;}
//many other goes here


Look as the nesting increase everytime to define a function, you need to write fully specified name of the function (repeating namespaces again again).

Second one :

#include "test.h"
namespace test{
namespace subtest{
int Foo(int x){return x;}
//other go here
}
}


This solves namespace name repetition also you can easily refactor things. To debug or refactor a namespace's content simply jump to it's first declaration and change the things. You can also collapse the code under single namespace. (With most ide) making you code more beautiful.

Similarly for multiple namespaces

First one :

#include "test.hpp"
int test1::Foo(int x){return x;}
int test2::Bar(int x){return x;}


How difficult it gets to debug things. Moreover if under two namespace same function name occurs you will have good time debugging.

Second one :

#include "test.hpp"
namespace test1{
int Foo(int x){return x;}
}
namespace test2{
int Bar(int x){return x;}
}


All the declaration within a namespace will be together. So debugging and jumping within namespace will be ease.

Also most open source projects use second implementation

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