can i include a file whose path is from a string variable?

Question

i think in python:

i can use:

def include_something(s):
  exec('import %s'%(s))

to import package dynamically

but in c++:

void include_something(const std::string& v) {
  # include v.c_str();
}

seems doestnt work.

So, is there any methods can do this? and will the futures c++ support this kind of function?

No, you can't. #include is a compile time directive (more precise, pre-compile time). v.c_str() is a runtime value. You can achieve something similar by loading shared libraries in runtime. — 3CEZVQ
– 3CEZVQ, Commented May 17, 2021 at 5:41
Please, remember that Python is an interpreted language. Hence, such a construct is possible. C++ is a compiled language where compile time and runtime are distinct. — Scheff's Cat
– Scheff's Cat, Commented May 17, 2021 at 6:22
@Sourabh because i have a directory saves a lot of header(they are come from other people, and i need to include them all to load function) — user15924460
– user15924460, Commented May 19, 2021 at 5:25
@user15924460 then how does that make you think you need to include source code files at run time? — phuclv
– phuclv, Commented May 23, 2021 at 2:59

Deumaudit · Accepted Answer · 2021-05-17 06:56:16Z

2

Simple answer: No, You can't

Answer with details: You can't do this with either include or import. As You can see on the picture below, include works on preprocess time, and import works on precompile time. While c_str is running at compile time (if it is constexpr), or at run time (if casual class or function), therefore, in any case, the import(or include) will be completed before the program learns the name of the module source of image

edited May 17, 2021 at 6:56

answered May 17, 2021 at 6:44

Deumaudit

1,0269 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Volodymyr Boyko Over a year ago

"import works on precompile time" what do you mean by that? precompile is cpython optimization

Timo Over a year ago

Did you make this image? If not, could you please provide the source? I guess it's from an article and I want to read it.

Deumaudit Over a year ago

@VolodymyrBoiko I haven't found any official information about exact moment, when modules works(but it's unambiguously before compilation), so in this case I shared info from another site(link under image)

Sourabh · Accepted Answer · 2021-05-23 10:05:02Z

0

There is no way in C/C++ to achieve dynamic header loading.

BUT

I'll do as the following:

Create a simple PowerShell script to create a master header file, that will contain all the headers from a given directory.

$source_dir = "C:\Program Files (x86)\Windows Kits\10\Include\10.0.14393.0\um\alljoyn_c\"
$master_headerfile = 'master.h'

Remove-Item $master_headerfile

New-Item $master_headerfile -ItemType File -Value "// Master header file`n"

Get-ChildItem $source_dir -Filter *.h |
Foreach-Object {

    Add-Content $master_headerfile "#include `"$_`""

}

Output will be

Now just include this master.h in your source file.

I hope, it will help you.

Thanks :)

answered May 23, 2021 at 10:05

Sourabh

3101 silver badge9 bronze badges

Collectives™ on Stack Overflow

can i include a file whose path is from a string variable?

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related