CODEWITHSUNDEEP
c++
Jimm
Jimm

Reputation: 8505

what is c++ modules and how do they differ from namespaces?

I was looking at libstdc++ documentation at http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a01618.html and found it arranged in "modules" such as Algorithm, Strings etc

I have multiple questions

  1. Since this is auto-generated documentation from doxygen, which part of libstdc++ source code or config file, makes doxygen "aware" of different modules and their contents/dependencies?

  2. What is modules and how does it differ from namespace.

  3. I did a google search on c++ modules and found that modules are defined by "export modulename", but i could not find any export definition in libstdc++ source code. Does the word "Modules" in the above documentation refer to some different construct than export ?

  4. Do developers typically divide their source code into modules for large projects?

  5. where can i learn about modules, so that i can organize my source code into modules and namespaces

Upvotes: 3

Views: 3062

Answers (2)

Jerry Coffin
Jerry Coffin

Reputation: 490308

It looks to me like you're running into two entirely separate things that happen to use the same name.

The "modules" you're seeing in the documentation seem to be just a post-hoc classification of the algorithms and such. It may be open to argument that they should correspond closely to namespaces, but in the case of the standard library, essentially everything is in one giant namespace. If it were being designed using namespaces from the beginning it might not be that way, but that's not how things happened. In any case, the classification applies to the documentation, not to the code itself. Somebody else producing similar documentation might decide to divide it up into different modules, still without affecting the code.

During the C++11 standardization effort, there was a proposal to add something else (that also went by the name modules) to the C++ language itself. This proposal was removed, primarily in the interest of finishing the standard sooner. The latter differed from namespaces quite a bit, and is the one that used "export" for a module name. It's dead and gone (a least for now) though, so I won't go into a lot more detail about it here. If you're curious, you can read Daveed Vandervoorde's paper about it though.

Update: The committee added modules to C++ 20. What was added is at least somewhat different from anything anybody would have known about in 2012 when this question was asked, but it is at least pretty much the same general idea as the modules that were proposed for C++11. A bit much to add on to a 10 year-old answer, but here's a link to at least some information about them:

https://en.cppreference.com/w/cpp/language/modules

Upvotes: 3

Kyle Lutz
Kyle Lutz

Reputation: 8036

The modules you see in the documentation are created by Doxygen and are not a part of C++. Certain classes in libstdc++ library are grouped together into modules using the \ingroup Doxygen command.

See: http://www.doxygen.nl/manual/grouping.html for more information on creating modules/groups in Doxygen.

Upvotes: 2

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