C++ #include<XXX.h> 相当于 Python 的 import XXX as X

Question

I work with Python most of the time, for some reasons now I also need to use C++.

I find Python's import XXX as X very neat in the following way, for example:

import numpy as np
a = np.array([1,2,3])

where I'm very clear by looking at my code that the array() function is provided by the numpy module.

However, when working with C++, if I do:

#include<cstdio>
std::remove(filename);

It's not clear to me at first sight that remove() function under the std namespace is provided by <cstdio> .

So I'm wondering if there is a way to do it in C++ as the import XXX as X way in Python?

Answer 1

Nope.

It'll be slightly clearer if you write std::remove (which you should be doing anyway; there's no guarantee that the symbol is available in the global namespace) because then at least you'll know it comes from a standard header.

Beyond that, it's up to your memory. 😊

Some people try to introduce hacks like:

namespace SomeThing {
   #include <cstdio>
}

// Now it's SomeThing::std::remove

That might work for your own headers (though I'd still discourage it even then). But it'll cause all manner of chaos with standard headers for sure and is not permitted:

[using.headers]/1: The entities in the C++ standard library are defined in headers, whose contents are made available to a translation unit when it contains the appropriate #include preprocessing directive .

[using.headers]/3: A translation unit shall include a header only outside of any declaration or definition, and shall include the header lexically before the first reference in that translation unit to any of the entities declared in that header. No diagnostic is required.

Recall that #include and import are fundamentally different things. C++ modules may go some way towards this sort of functionality, perhaps, but by including source code you are not even touching namespaces of symbols created by that code.

Answer 2

No there is no way to force this syntax . The person who developped the code that you include is free. Generally people split their code into namespaces, which can result to this syntax:

#include <MyLibrary.h>

int main()
{
    MyLibrary::SayHello();
    return 0;
}

But you have no guarentee on how the code in the header is written.

Answer 3

C++ #include<XXX.h> equivalent of Python's import XXX as X

There is no equivalent in C++.

When you include a file into another, you get every single declaration from the included file, and you have no option of changing their names.

You can add aliases for types and namespaces though, and references to objects, as well as write wrapper functions to do some of what the as X part does in Python.

It's not clear to me at first sight that remove() is provided by <cstdio> .

The std namespace at least tells you that it is provided by the standard library.

What I like to do, is document which header provides the used declarations:

#include<cstdio>  // std::remove
std::remove(filename);

That said, most IDE's can show you where an identifier is declared by ctrl-clicking or hovering over it (although this doesn't always work well when there are overloads in different headers). My primary use for inclusion comments is checking which includes can be removed after refactoring.