GCC如何使用c++20模块？

Question

我目前正在尝试新的C++20的特性，如使用GCC 10.1.0描述的模块，但是如果我试图构建下面的代码片段，编译器会抛出一大堆错误。

这就是我到目前为止写的片段：

// helloworld.cpp
export module helloworld;  // module declaration
import <iostream>;         // import declaration
 
export void hello() {      // export declaration
    std::cout << "Hello world!\n";
}

// main.cpp
import helloworld;  // import declaration
 
int main() {
    hello();
}

我正在使用g++ helloworld.cpp main.cpp -std=c++20编译它。

编译器给了我这个错误：

helloworld.cpp:2:1: warning: keyword ‘export’ not implemented, and will be ignored
    2 | export module helloworld;  // module declaration
      | ^~~~~~
helloworld.cpp:2:8: error: ‘module’ does not name a type
    2 | export module helloworld;  // module declaration
      |        ^~~~~~
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
    3 | import <iostream>;         // import declaration
      |         ^~~~~~~~
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:9: error: ‘iostream’ was not declared in this scope
helloworld.cpp:3:1: error: ‘import’ does not name a type
    3 | import <iostream>;         // import declaration
      | ^~~~~~
helloworld.cpp:5:1: warning: keyword ‘export’ not implemented, and will be ignored
    5 | export void hello() {      // export declaration
      | ^~~~~~
helloworld.cpp: In function ‘void hello()’:
helloworld.cpp:6:10: error: ‘cout’ is not a member of ‘std’
    6 |     std::cout << "Hello world!\n";
      |          ^~~~
helloworld.cpp:1:1: note: ‘std::cout’ is defined in header ‘<iostream>’; did you forget to ‘#include <iostream>’?
  +++ |+#include <iostream>
    1 | // helloworld.cpp
main.cpp:2:1: error: ‘import’ does not name a type
    2 | import helloworld;  // import declaration
      | ^~~~~~
main.cpp: In function ‘int main()’:
main.cpp:5:5: error: ‘hello’ was not declared in this scope
    5 |     hello();
      |     ^~~~~

我做错什么了？

Answer 1

GCC的语言状态页面说它还不支持模块。

C++20支持是不完整的(考虑到我们在2020年，这是足够公平的！)C++20技术上还不存在…)。

但是，使用一些标志和一个开发分支，您可以使用正在进行中的实现--在GCC模Wiki上阅读更多有关它的信息。

GCC 10的默认语言版本是C++14；GCC 11 up to C++17。

Answer 2

我在23.1.21的时候看到了GNU gcc的网站，它说你必须包括一个名为-fmodules ts的旗帜。以下是该网站的链接，以获取其他信息https://gcc.gnu.org/wiki/cxx-modules

Answer 3

现在，如果你用GCC的话，你就可以完成：

# g++ -std=c++20 -fmodules-ts hello.cpp -o hello.exe -x c++-system-header iostream

来自：https://stackoverflow.com/a/73643558/19946116

如果您更喜欢Visual 2022，则需要配置它：https://stackoverflow.com/a/73643523/19946116。