问题描述
模块是可能添加到C ++ 1z的#includes的替代品。 。
使用
import std.io;
无法正常工作（编译），因为C ++ 1z规范模块（包括语法）不是最终的。
in a C++ source file does not work (compile) yet, as the C++1z specification for modules (which includes syntax) isn't final.
指出，当传递 -fmodules 标志时，#includes将被重写到他们适当的进口。然而，检查预处理器建议另外（test.cpp只包含 #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, ...);
$ b > vs没有标志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.
我做错了什么？
推荐答案
像你提到的，clang还没有一个C ++语法的导入，
所以我怀疑 #include 指令将在预处理文件时被重写为导入，因此这可能不是测试模块是否按预期工作的最佳方式。
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，如果你显式地设置 -fmodules-cache-path =< path> ，你可以在构建过程中观察到用预编译的模块文件有任何模块涉及。
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.
您需要使用libc ++（似乎是一个module.modulemap从3.7.0版本）如果你想使用模块启用标准库现在 - 虽然在我的经验，这不是完全正在工作。
（Visual Studio 2015的C ++编译器也应该获得某种形式的模块支持与11月的更新1）
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，你仍然可以使用模块在你自己的代码。 clang文档包含的详细说明，但
我还设置了一个示例项目（使用cmake），应该生成一个高速缓存目录，包含一些模块。
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, butI've also set up a little example project here (using cmake) that should generate a cache directory with some modules when built.
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