C++

Forum

 
C++20 import issue

chipp (776)
i tried to code in C++20 and tried to import header file but it doesn't worked

anyone knows why?

IDE i'm using is Visual Studio 2022

my code is like this:

1
2
3
4
5
6
7
8
9
 
import <iostream>;

int main () {
	std::cout << "iostream imported" << std::endl;

	//...

	return 0;
}
Ch1156 (1999)
Is your project settings set to use c++ 20?

Go to Project > Your Project Name > General > C++ Language Standard

You may need to use Latest instead of C++ 20, but try 20 first

Then under C/C++ > language > Build ISO C++ 23 Standard Library Modules

Also enable Experimental C++ library Modules

Set both to to yes

Also right click your .cpp file in the solution explorer and go to Properties > advanced > Compile as > Compile as C++ Module Code (/interface )

Does that work?
Last edited on
seeplus (6589)
use import std; which imports all of std::

1
2
3
4
5
 
import std;

int main() {
	std::cout << "Hello world\n";
}

Last edited on
mbozzi (3932)
deleted account xyzzy (5768)
In my experience with Visual Studio 2022 and C++20 modules there is no need to enable the Experimental C++ Standard Library Modules or enabling ISO C++23 Standard Library Modules if you import individual modules that are also C++ headers such as <iostream>.

Your language standard must be at least std:c++20 To use that form of importing stdlib headers/modules.

If you use import std; the language standard must be std:c++latest. No need to enable the experimental or C++23 modules that I've run across.

Intellisense sometimes has issues when using modules, though the code compiles without a problem. Especially if you use import std;.

It is possible to change defaults like the C++ language standard globally in the VS IDE so every new project/solution uses std:c++20 or std::c++latest instead of the default C++14 language standard. You can also change/update other properties to be default such as the experimental C++ and C++23 stdlib modules setting. Doing it requires a bit of work, but it is worth the effort IMO.

Visual Studio - Connecting a Library
https://cplusplus.com/forum/lounge/271176/#msg1169093

I did this so every new project uses C++20 as the default language standard. I set this up before C++23 was an option in the property pages, and never had a need for the experimental C++ stdlib modules. I will probably change those default properties in the near future.
chipp (776)
@ch1156: thanks!! it's working!!


You may need to use Latest instead of C++ 20, but try 20 first


but there's no "Latest" option

https://imgur.com/a/VzxIaZY

nevertheless, it is already working... thanks, bro!

@george: ok, thanks fyi

so, you're saying that i just have to set both of those to "No"?
Last edited on
seeplus (6589)
but there's no "Latest" option


That's the preview option....
deleted account xyzzy (5768)
but there's no "Latest" option

Look at the option below C++20, the one that is marked "Preview".

Far right shows "std:c++latest".

so, you're saying that i just have to set both of those to "No"?

You don't have to do anything, the defaults are already set so you don't use the experimental C++20 standard library modules, the option is blank, and the C++23 standard library modules option is set to No.

If you choose to use C++23 import modules, import std; for example, then you have to set the C++ language standard to Preview/std:c++latest.

Personally I prefer to specify what modules my code consumes by providing the module name. import <iostream>; for example.

Doing that makes modularizing old pre-C++20 code easier since the change is changing #include to import and add the semicolon at the end.

Since VS is not 100% C++23 compliant yet at this time I stay with the C++20 language standard. I'm still getting to know what C++20 added to the language toolbox, learning what C++23 offers is "in the future."

Intellisense in the VS IDE even with C++20 goes kinda loopy. With C++23 it goes really bonkers, flagging code as errors that aren't. Code that compiles without any issues.
Topic archived. No new replies allowed.