如何在Clang中使用C ++模块？ [英] How do I use C++ modules in Clang?

问题描述

模块是#includes的替代方法。 C语C ++的完整实现。如果要立即使用Clang使用模块，该怎么办？

Modules are an alternative to #includes. Clang has a complete implementation for C++. How would I go about if I wanted to use modules using Clang now?

使用

import std.io;

尚无法正常工作（编译），因为模块规范（包括

in a C++ source file does not work (compile) yet, as the specification for modules (which includes syntax) isn't final.

Clang文档指出，传递 -fmodules 标志时，＃includes将改写成适当的进口。但是，检查预处理器会建议其他方式（test.cpp仅包含 #include< stdio.h> 和一个空的main）：

The Clang documentation states that, when passing the -fmodules flag, #includes will be rewritten to their appropriate imports. However, checking the preprocessor suggests otherwise (test.cpp only contains #include <stdio.h> and an empty main):

$ clang++-3.5 -fmodules -E test.cpp -o test
$ grep " printf " test
extern int printf (const char *__restrict __format, ...);

此外，使用 -fmodules vs根本没有标志会产生相同的目标文件。

Furthermore, compiling this test file with -fmodules vs no flags at all produces the same object file.

我在做什么错了？

推荐答案

就像您提到的那样，clang尚无用于导入的C ++语法，
，因此我怀疑 #include 指令是否会在预处理文件时，将其按字面意思重写为导入，因此这可能不是测试模块是否按预期工作的最佳方法。

Like you mentioned, clang does not yet have a C++ syntax for imports, so I doubt that #include directives are going to be literally rewritten as imports when preprocessing a file, so that may not be the best way to test if modules are working as intended.

但是，如果您显式设置 -fmodules-cache-path =< path> ，则可以在构建过程中观察到用预编译模块文件（* .pcm）填充clang的情况-如果涉及任何模块。

However, if you set -fmodules-cache-path=<path> explicitly, you can observe clang populating it with precompiled module files (*.pcm) during a build - if there are any modules involved.

如果要使用启用了模块的标准库，则需要使用libc ++（似乎与3.7.0版的module.modulemap一起提供）现在-尽管根据我的经验，这还不能完全解决。
（Visual Studio 2015的C ++编译器也应该在11月的Update 1中获得某种形式的模块支持）

You'll need to use libc++ (which seems to come with a module.modulemap as of version 3.7.0) if you want to use a modules enabled standard library right now - though in my experience this isn't working entirely just yet. (Visual Studio 2015's C++ compiler is also supposed to get some form of module support with Update 1 in November)

独立于stdlib，您仍然可以使用您自己的代码中的模块。叮叮文档包含模块映射语言的详细说明

Independently of the stdlib, you could still use modules in your own code. The clang docs contain a detailed description of the Module Map Language.

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