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c++templatesnamespacesincludeheader-files
danijar
danijar

Reputation: 34175

Using namespaces inside template implementation files

To keep class definition in header file clean, I decided to move implementations of templated functions into another *.h file, which I include in the main header. Now I would like to make use of using namespace there, to make code more readable.

But using namespaces would affect the whole application, since the file gets included in the header which itself gets included in the whole application. The using of the namespaces would spread out of the file.

How can I handle this?

Upvotes: 1

Views: 894

Answers (3)

Joe Z
Joe Z

Reputation: 17926

You can put using namespace XX inside function definitions to scope the using declaration to that function:

int func( ...args... )
{
    using namespace std; 
    // ... body of function
}

Upvotes: 4

Steve Van Opstal
Steve Van Opstal

Reputation: 1111

You can place the using namespace in the namespace of your 'main header':

Header.h

#include <string>

namespace Test
{
    using namespace std;

    string f()
    {
        return "Test";
    };
}

main.cpp

#include "Header.h"

int main()
{
    Test::f();  

    string test;        // Error: identifier "string" is undefined
    std::string test;   

    return 0;
}

Upvotes: 1

NicholasM
NicholasM

Reputation: 4673

Use a namespace alias.

namespace submod_ = topspace::other_project::module::submodule;

Then you can use submod_ wherever you would require the very long namespace.

This requires you to still use submod_ where you would have the long namespace qualifier. In that sense, it doesn't exactly answer your question. But I would argue that the explicitness of the qualification aids readability and helps prevent mistakes.

There are real examples of StackOverflow questions where a "using" declaration brought in "lurking" functions which the code author did not realize.

Upvotes: 1

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