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C++ Modules

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By Xiong Ding 1 min read

Why do we have header files?

p0132r0 is a great manuscript about the history and problems with using header files. To sum up, C/C++ files has a notion called independent compilation, which means each translation unit is processed independently. For a translation unit to use a function in another translation unit, we should use keyword extern, and it is the linker’s duty to figure out the correct source that provides the implementation. However, what if multiple translation units want to use the same function? Each of them needs an exact same extern statement, which is error-prone and hard to refactor. That is why header files come to rescue.

What problems does this header file approach have? One obvious issue is the long build time. A bigger problem, in my opinion, is the interaction with ODR (one definition rule).

Current status

So far, neither clang nor gcc supports syntax import std.vector or import <vector>. We should use #include inside global module.

programming-language, cpp
cpp
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