Hello World C++ 23

[Brad Jones]

Okay -

Very basic question. The following is a simple C++ 23 (or C++ 20) listing. It uses import to pull in iostream. I'm using gcc 13 and want to compile this listing. It doesn't, however, like the import. I tried compiling with the -std=c++2a option, but that didn't help.

import <iostream>;


using namespace std;


int main()
{ 
   std::cout << "Hello, World!" << std::endl;
   return 0;
}

Any suggestions on what I might be doing wrong or what I need to do to get this listing to compile using the import? (yeah, I know I can change it to #include, but that defeats the C++ 20/23 usage.

(error is 'import' does not name a type....

[2kaud]

I can't comment on gcc as I don't use it. But this is OK with VS2022 as C++23 (preview set for C++ language standard option):

import std;

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

[Brad Jones]

D'oh. Thanks. It's amazing what trouble having one little setting wrong can do. Hours down a rabbit hole.

Sometimes a person needs to step back and think simpler. Your post helped me do that, so thanks!

Brad!

[VictorN]

I can't comment on gcc as I don't use it. But this is OK with VS2022 as C++23 (preview set for C++ language standard option):

import std;

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

And trying to compile in VS2022 with C++20 causes the similar errors as Brad! with gcc had.

[2kaud]

compile in VS2022 with C++20

C++20? So last year!

With modules the standard library will no longer be split into tons of small little headers. Instead you'll just do import std; and that's it. Module support for the standard library is part of C++23 however, not C++20.

There's also std.compat which exports everything in std and also adds the C runtime global namespaces.

Because named modules don't expose macros, macros like assert, errno, offsetof, va_arg, and others aren't available when you import std or std.compat

See:
https://learn.microsoft.com/en-us/cp...?view=msvc-170

[Juliadyer]

GCC 13 doesn?t fully support import for standard headers like <iostream> yet. For now, stick with #include <iostream>. Use -std=c++23 for C++23 features, but import <iostream> won?t work until future compiler updates improve module support.
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