# Anyway to automatically add include dir when using target\_link\_libraries?

**URL:** <https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811>\
**Category:** Code\
**Created:** [February 22, 2021, 8:46am UTC](https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811 "2021-02-22T08:46:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![psionic12](https://discourse.cmake.org/user_avatar/discourse.cmake.org/psionic12/32/998_2.png) [@psionic12](https://discourse.cmake.org/u/psionic12)\
**Post date:** [February 22, 2021, 8:46am UTC](https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811/1 "2021-02-22T08:46:32Z")

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Hi, when I wrote libraries, I was wondering is there anyway I can expose my headers automatically when someone using `target_link_libraries` to link my lib? Usually, when we use some libraries, even if most libraries offer some variables to hold headers’ path, we should manually write `target_include_directories` along with `target_link_libraries`.

So if I’m writing a library, is there any mechanism, so that users can automatically include headers just using `target_link_libraries`？

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**Author:** ![Angew](https://discourse.cmake.org/user_avatar/discourse.cmake.org/angew/32/229_2.png) [@Angew](https://discourse.cmake.org/u/Angew)\
**Post date:** [February 22, 2021, 8:50am UTC](https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811/2 "2021-02-22T08:50:13Z")

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Indeed there is, the CMake term for this is “usage requirements.” It’s covered in [CMake documentation](https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#build-specification-and-usage-requirements) which is well worth reading, but here’s a quick code sample to get you started:

```auto
# Define your library and its usage requirements:
add_library(MyLib ...)
target_include_directories(MyLib PUBLIC pub/inc1) # These will be used both by the library and by whoever links to it
target_include_directories(MyLib PRIVATE src) # These will be used only when building the library, not by its clients

```

Include directories (and copile definitions, and compile options, and link options, and linked libraries, …) which are specified using `PUBLIC` are used when building the library itself, and also added to whoever’s consuming the library. Those added with `PRIVATE` are used only when building the library. (And for completeness, those added with `INTERFACE` are added _only_ to the consumers who link against the library, but are not used when building the library itself).

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**Author:** ![psionic12](https://discourse.cmake.org/user_avatar/discourse.cmake.org/psionic12/32/998_2.png) [@psionic12](https://discourse.cmake.org/u/psionic12)\
**Post date:** [February 22, 2021, 9:00am UTC](https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811/3 "2021-02-22T09:00:49Z")

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Hi @Angew, thank very much for helping, I’m curious that why plenty of libraries I use still need to manually include headers (especially when using `find_package`)? Does it due to the project mixed public and private headers in the same directory?

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**Author:** ![Angew](https://discourse.cmake.org/user_avatar/discourse.cmake.org/angew/32/229_2.png) [@Angew](https://discourse.cmake.org/u/Angew)\
**Post date:** [February 22, 2021, 9:05am UTC](https://discourse.cmake.org/t/anyway-to-automatically-add-include-dir-when-using-target-link-libraries/2811/4 "2021-02-22T09:05:32Z")

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Usage requirements other than transitive linking were first introduced to CMake in 2.8.11, and support/infrastructure for them is expanding gradually. So they are newer than a lot of projects’ CMake support, meaning those projects may be reluctant to rewrite their build specification to support them.