When include libraries in .cpp files?

Question

Header are used to separate "declaration" (.h files) from "implementation" (.cpp files), but also to import librareis, so usually there is no #include ..." in the .cpp file.

But let suppose that some-library.h is needed only for some operation done inside a particular implementation of foo() in some .cpp file: should I #include "some-library.h" in the .h file (where the foo() is declared) or include it in the .cpp file (where foo() is implemented)?

I would say the second, since the library is needed only for the implementation, but I would prefer an answer from someone more expert than me on the topic.

Headers aren't used "to import libraries". The only way that could work is if a library was all in one header file, and there had no compiled component. — juanchopanza
– juanchopanza, Commented May 3, 2016 at 8:02

Humam Helfawi · Accepted Answer · 2016-05-03 07:03:01Z

5

You should include your library just where you are using it. If there is no use of the library in your header file then do not include it.

Including it in the header will bring you a lot of headache. For example, you have to distribute it with your project (if your output is a library).

answered May 3, 2016 at 7:03

Humam Helfawi

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3 Comments

jcai Over a year ago

It may also increase compile times if you include header files needlessly.

Eissa N. Over a year ago

It is a good practice to use forward declaration, whenever possible, rather than including a header file.

juanchopanza Over a year ago

I think you're failing to address OP's confusion regarding headers and libraries.

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