C ++模块导入链导致奇怪的编译器错误 [英] C++-module import chain results in strange compiler errors

问题描述

使用clang编译c ++-20模块时.导入文件时，导入另一个文件，然后再导入第三个文件时，出现奇怪的编译错误:

When compiling c++-20 modules with clang. I get strange compilation errors when importing a file that imports another file that imports a third file like so:

// a.cppm
#include <string>

export module a;

export std::string getStuffA() {
  return "a";
}

// b.cppm
#include <string>

import a;

export module b;

export std::string getStuffB() {
  return "b" + getStuffA();
}

// c.cpp
#include <string>

import b;

int main() {
  std::cout << getStuffB() << std::endl;
  return 0;
}

编译器输出:

In file included from ./src/c.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/iostream:39:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/ostream:38:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/ios:44:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/basic_ios.h:37:
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/locale_facets.h:2569:5: error: inline declaration of 'isspace' follows non-inline definition

它列出了一些似乎同时具有内联和非内联定义的函数，例如isprint，iscntrl，isupper.

And it lists some more functions that seems to have both inline and non-inline definiton, like isprint, iscntrl, isupper.

有什么办法可以解决这些错误.

Is there any way to get around these errors.

注意:删除 std :: string 和 #include< string> 会删除编译错误，因此我认为这些错误来自< string>

Note: Removing std::string and #include <string> removes the compilation errors, so I think that the errors comes from <string>

推荐答案

如前所述，gcc 11支持模块，并且您正在尝试将glang与gcc 10标准C ++库一起使用.

As already said, modules are supported in gcc 11, and you are trying to use clang with gcc 10 standard C++ library.

使用正确的C ++标准库，预处理器include指令(例如 #include< string> )将自动映射到 import< string> ;; .对于不支持模块的gcc 10使用标准的C ++库，您将得到诸如所得到的错误.

With using the proper C++ standard library, preprocessor include directives such as #include <string> will be automatically mapped to import <string>;. With using the standard C++ library for gcc 10, that does not support modules, you will get errors such as you have got.

如果使用支持模块的clang，并且似乎正在使用这种现代clang，否则在import指令上会遇到另一个错误，则应使用clang C ++标准库: -stdlib = libc ++ .

If you use clang, that supports modules, and it seems you are using such modern clang, otherwise you would get another errors on the import directive, you should use the clang C++ standard library: -stdlib=libc++.

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