# Right way to look for include files in standard system directories?
**URL:** https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071
**Category:** Usage
**Created:** [October 26, 2020, 3:44pm UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071 "2020-10-26T15:44:05Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@tomoreilly](https://discourse.cmake.org/u/tomoreilly)
#### Post date: [October 26, 2020, 3:44pm UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071/1 "2020-10-26T15:44:05Z")
Pardon my very newbie question - I want cmake to look in “standard” system locations for installed third-party headers - how to do that in a portable way? The variable [CMAKE\_SYSTEM\_INCLUDE\_PATH](https://cmake.org/cmake/help/v3.3/variable/CMAKE_SYSTEM_INCLUDE_PATH.html) looks promising, e.g. as a “hint” to find\_file(), but on my ubuntu 18.03 system CMAKE\_SYSTEM\_INCLUDE\_PATH just contains /usr/include/X11. Do I have to manually include “/usr/local/include” in the hints to find\_file()?
Thanks!
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### Author:  [@scivision](https://discourse.cmake.org/u/scivision)
#### Post date: [October 26, 2020, 5:57pm UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071/2 "2020-10-26T17:57:46Z")
Hi Tom, I think [CMAKE\_INCLUDE\_PATH](https://cmake.org/cmake/help/latest/variable/CMAKE_INCLUDE_PATH.html) might be the place to put this.
It sounds like your CMake script is using `find_file()` directly. You could use PATHS or HINTS of find\_file() directly in your CMake script, or use CMAKE\_INCLUDE\_PATH to more generically add include search path for all the find\_file().
I run into this kind of issue for example when using Homebrew on MacOS, needing to add the Homebrew location like this.
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### Author:  [@tomoreilly](https://discourse.cmake.org/u/tomoreilly)
#### Post date: [October 26, 2020, 6:11pm UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071/3 "2020-10-26T18:11:09Z")
Thanks @scivision. So how/where does CMAKE\_INCLUDE\_PATH get set to a “reasonable” value for the host where you are building, e.g. on MacOS? Is there some way that cmake can detect that? That is the part I think I am missing…
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### Author:  [@robert.maynard](https://discourse.cmake.org/u/robert.maynard)
#### Post date: [October 26, 2020, 7:46pm UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071/4 "2020-10-26T19:46:19Z")
All the find commands including `find_file` will search `/usr/local` on Linux. This is done as `/usr/local` is contained in `CMAKE_SYSTEM_PREFIX_PATH`.
For example if we have the following code:
```cmake
find_file(FakeFileVar FakeFile.xyz)
```
We can use CMake 3.17+ and to verify the searching with `cmake -B --debug-find` and looking at the output. As shown below we can see CMake searching `/usr/local/include`
```auto
Running with debug output on for the `find` commands.
CMake Debug Log at CMakeLists.txt:7 (find_file):
find_file called with the following settings:
VAR: FakeFileVar
NAMES: "FakeFile.xyz"
Documentation: Path to a file.
Framework
Only Search Frameworks: 0
Search Frameworks Last: 0
Search Frameworks First: 0
AppBundle
Only Search AppBundle: 0
Search AppBundle Last: 0
Search AppBundle First: 0
CMAKE_FIND_USE_CMAKE_PATH: 1
CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH: 1
CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH: 1
CMAKE_FIND_USE_CMAKE_SYSTEM_PATH: 1
find_file considered the following locations:
/usr/local/sbin/FakeFile.xyz
/usr/local/bin/FakeFile.xyz
/usr/sbin/FakeFile.xyz
/usr/bin/FakeFile.xyz
/sbin/FakeFile.xyz
/bin/FakeFile.xyz
/usr/games/FakeFile.xyz
/usr/local/games/FakeFile.xyz
/usr/local/include/x86_64-linux-gnu/FakeFile.xyz
/usr/local/include/FakeFile.xyz
/usr/local/FakeFile.xyz
/usr/include/x86_64-linux-gnu/FakeFile.xyz
/usr/include/FakeFile.xyz
/usr/FakeFile.xyz
/include/x86_64-linux-gnu/FakeFile.xyz
/include/FakeFile.xyz
/opt/cmake-3.17/include/x86_64-linux-gnu/FakeFile.xyz
/opt/cmake-3.17/include/FakeFile.xyz
/opt/cmake-3.17/FakeFile.xyz
/usr/X11R6/include/x86_64-linux-gnu/FakeFile.xyz
/usr/X11R6/include/FakeFile.xyz
/usr/X11R6/FakeFile.xyz
/usr/pkg/include/x86_64-linux-gnu/FakeFile.xyz
/usr/pkg/include/FakeFile.xyz
/usr/pkg/FakeFile.xyz
/opt/include/x86_64-linux-gnu/FakeFile.xyz
/opt/include/FakeFile.xyz
/opt/FakeFile.xyz
/usr/include/X11/FakeFile.xyz
The item was not found.
```
---
### Author:  [@michael\_ch](https://discourse.cmake.org/u/michael_ch)
#### Post date: [September 6, 2022, 9:29am UTC](https://discourse.cmake.org/t/right-way-to-look-for-include-files-in-standard-system-directories/2071/5 "2022-09-06T09:29:22Z")
It has been a long time since the question was posted but I am leaving this one just for reference. I have a blog post describing step-by-step almost what you (or anyone else) were trying to do.
I don’t know if it is the perfect example, but here it is: [Shared lib to be used by client programs with CMake](https://michae9.wordpress.com/2022/09/01/shared-lib-to-be-used-by-client-programs-with-cmake/)
p.s.: sorry for posting a link to my blog but the post is way too big to repost it here.