# FindBoost difference between Boost\_INCLUDE\_DIR and Boost\_INCLUDE\_DIRS
**URL:** https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855
**Category:** Code
**Created:** [March 25, 2020, 9:07am UTC](https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855 "2020-03-25T09:07:26Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@MonkeyBreaker](https://discourse.cmake.org/u/MonkeyBreaker)
#### Post date: [March 25, 2020, 9:07am UTC](https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855/1 "2020-03-25T09:07:26Z")
Hi everyone,
Question is about the difference of using `Boost_INCLUDE_DIR` and `Boost_INCLUDE_DIRS` to indicate where boost header files are in the system.
As I understood so far from the documentation and from different posts on SO and other forums:
- Boost\_INCLUDE\_DIR is cached after a first run of cmake in the project
- Boost\_INCLUDE\_DIRS is set each time that cmake is run in the project
From the examples in the documentation, `Boost_INCLUDE_DIRS` is the variable used to indicate where boost header files are in the system.
But my question is, if we decided to use `Boost_INCLUDE_DIR`, should results be different that with `Boost_INCLUDE_DIRS` ?
Because in our library, we decided to go with `Boost_INCLUDE_DIR`, it worked so far. But one developer encountered an error because `Boost_INCLUDE_DIR` was empty (it was not Boost\_INCLUDE\_DIR-NOT\_FOUND) and `Boost_INCLUDE_DIRS` was correctly set.
Our CMake scripts only does the following:
```auto
find_package(Boost 1.56 REQUIRED)
include_directories(${Boost_INCLUDE_DIR})
```
Thank you for any insights on the issue and have a nice day.
Julián
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 25, 2020, 11:36am UTC](https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855/2 "2020-03-25T11:36:34Z")
`Boost_INCLUDE_DIR` is the directory Boost found for itself. This does not happen for `BoostConfig.cmake` based searches. `Boost_INCLUDE_DIRS` is the list of include directories needed to use Boost. This should include any directories to dependencies needed.
---
### Author:  [@MonkeyBreaker](https://discourse.cmake.org/u/MonkeyBreaker)
#### Post date: [March 25, 2020, 12:30pm UTC](https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855/3 "2020-03-25T12:30:29Z")
Thank you for the answer !
I understand, but maybe the current naming or description of the variables is a bit confuse, what do you think ?
Because even in forums, the confusion happen, see:
- [this](https://stackoverflow.com/a/3813010): tells users to go with `Boost_INCLUDE_DIR`
- [this](https://stackoverflow.com/a/6646518): tells users to go with `Boost_INCLUDE_DIRS`
Both answer are accepted ones.
In my opinion the confusion comes from the variable name.
Anyway, we’ll change from `Boost_INCLUDE_DIR` to `Boost_INCLUDE_DIRS` in our library.
Julián
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 25, 2020, 12:56pm UTC](https://discourse.cmake.org/t/findboost-difference-between-boost-include-dir-and-boost-include-dirs/855/4 "2020-03-25T12:56:00Z")
It’s a typical pattern that things directly found are singular while aggregates which may include dependencies is plural. Since `config.cmake` files don’t need to actually search for anything, the singular variants tend to not exist and only the plural versions are “end results” of the `find_package` call. There are some older modules which have not migrated to this usage pattern however.