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erlangdirectory-structureerlang-otp

Header files location for an Erlang/OTP application

Should I place .hrl header files of an Erlang/OTP application in the /src or the /include directory?

Solution

  • From: http://erlang.org/doc/design_principles/applications.html

    • src - Required. Contains the Erlang source code, the source of the .app file and internal include files used by the application itself. [...]
    • include - Optional. Used for public include files that must be reachable from other applications.

    This is also explained by: http://erlang.org/pipermail/erlang-questions/2009-July/045516.html

    Use Case 1: Your project has -defined constants, parse transforms, etc. which are required for others to use your code. Examples include qlc or webmachine.

    Solution: Put your .hrl files in /include. As long as your project is on the code path then clients of your code can use -include_lib() to load the .hrl files.

    Use Case 2: You've centralised common constants, etc. in a .hrl file. These constants are intended to be used internally by your project code. This means at no time will any client need access to them.

    Solution: Put your .hrl files in /src. Your code can use -include() to pull in the .hrl files.

    Keep in mind that both include directives are compile-time constructs. You can put all of your header files in /src, compile your code using -include(), and then selectively "export" the header files you want to publish by copying them into /include. I do this a lot since it makes my compile process easier -- no code path to futz with -- and it makes my client code cleaner -- they can use -include_lib() to find my public header files.

    --Kevin