# Weird variable behaviour with find\_package
**URL:** https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313
**Category:** Usage
**Created:** [May 13, 2021, 6:02pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313 "2021-05-13T18:02:39Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@LaXiS](https://discourse.cmake.org/u/LaXiS)
#### Post date: [May 13, 2021, 6:02pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/1 "2021-05-13T18:02:39Z")
Hello there,
I have already posted for help on Reddit ([here](https://www.reddit.com/r/cmake/comments/nayqf9/variable_still_empty_after_find_package/)), but I believe I might get more insightful help here.
My environment: Windows 10, latest MSYS2/MinGW64, CMake 3.20.2, Intel IPP 2021.2.0
My objective: include IPP libraries for use in my project.
My issue: when using `find_package` with Intel-provided `ipp-config.cmake`, some variables are set while others aren’t, even though they should.
I have installed Intel IPP using the official installer, which includes a CMake package config file in `C:\Program Files (x86)\Intel\oneAPI\ipp\2021.2.0\lib\cmake\ipp\ipp-config.cmake`. You can find its paste here: pastebin .com/j3r67M1N
This is my `CMakeLists.txt`:
```auto
cmake_minimum_required(VERSION 3.20)
project(MyProject)
find_package(IPP REQUIRED)
message("${IPP_FOUND} | ${IPP_SHARED} | ${IPP_ARCH} | ${IPP_TL_VARIANT} | ${IPP_LIBRARIES} | ${WIN32} | ${IPP_ippcore_FOUND}")
add_executable(MyExec src/main.cpp)
target_link_libraries(MyExec ${IPP_LIBRARIES})
```
This is the output in a MinGW64 bash shell:
```auto
$ /c/Program\ Files/CMake/bin/cmake.exe .. -G "MinGW Makefiles"
-- The C compiler identification is GNU 10.3.0
-- The CXX compiler identification is GNU 10.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/msys64/mingw64/bin/gcc.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/msys64/mingw64/bin/g++.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
1 | | intel64 | OpenMP | | 1 |
-- Configuring done
-- Generating done
-- Build files have been written to: C:/REDACTED/build
```
Minor doubt: how does CMake know to use `ipp-config.cmake` when there is neither a built-in nor user-provided FindIPP? All I can see is an environment variable called `ONEAPI_ROOT`, which points to `C:\Program Files (x86)\Intel\oneAPI`; is this enough for CMake to do its thing?
Actual issue: take a look at the output of the `message()` command; as you can see `IPP_FOUND`, `IPP_ARCH` and `IPP_TL_VARIANT` are correctly set as expected (to their defaults), while `IPP_LIBRARIES` and `IPP_ippcore_FOUND` aren’t.
I can confidently say that they are being set by IPP’s config, because when I added a `variable_watch(IPP_LIBRARIES)`, this was the output (full paste here: pastebin .com/gz2V5Ajh ), includes also a `set(IPP_LIBRARIES "WTF")` to make the issue more evident):
```auto
CMake Debug Log at C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake:128 (list):
Variable "IPP_LIBRARIES" was accessed using MODIFIED_ACCESS with value
"IPP::ipp_iw".
...
CMake Debug Log at C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake:128 (list):
Variable "IPP_LIBRARIES" was accessed using READ_ACCESS with value "".
...
CMake Debug Log at C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake:128 (list):
Variable "IPP_LIBRARIES" was accessed using MODIFIED_ACCESS with value
"IPP::ippcore".
```
I then tried with `target_link_libraries(MyExec IPP::ippcore)` and guess what, that worked. But `IPP_LIBRARIES` is still empty. What the hell?
Does anyone have any clue why the `list(APPEND IPP_LIBRARIES ...)` in IPP’s config is always appending to an empty/reset variable?
Thanks in advance
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [May 13, 2021, 6:27pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/2 "2021-05-13T18:27:48Z")
> [@LaXiS](#):
>
> Minor doubt: how does CMake know to use `ipp-config.cmake` when there is neither a built-in nor user-provided FindIPP?
The [documentation for `find_package`](https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure) describes this.
> [@LaXiS](#):
>
> But `IPP_LIBRARIES` is still empty. What the hell?
It might only be used inside of functions in the `ipp-config.cmake` call. I don’t think variables which go out of scope have `variable_watch` triggers called on them. I would recommend reading `ipp-config.cmake` yourself. It might have comments for usage and available libraries or targets at the top. Additionally, `cmake --trace-expand` can show the lines being executed and you can search it for `IPP_LIBRARIES` to trace its fate.
---
### Author:  [@LaXiS](https://discourse.cmake.org/u/LaXiS)
#### Post date: [May 13, 2021, 7:00pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/3 "2021-05-13T19:00:15Z")
Thank you Ben.
It still is not clear to me, the closest thing I found was the `ONEAPI_ROOT` environment variable, but I believe that would only work for `find_package(ONEAPI)`. Not even an entry in the Windows registry. Is there any debug/trace switch that logs the searched directories? Anyway, it’s not a big deal.
`ipp-config.cmake` explicitly says in its header (full paste [here](https://pastebin.com/j3r67M1N)):
```auto
# To use it, add the lines below to your CMakeLists.txt:
# ~~~
# find_package(IPP REQUIRED)
# target_link_libraries(mytarget ${IPP_LIBRARIES})
# ~~~
#
# List of the variables defined in this file:
#
# * IPP_FOUND
# * IPP_LIBRARIES - list of all imported targets
```
I ran CMake with `--trace-expand`, here are all relevant lines where `IPP_LIBRARIES` is involved:
```auto
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(52): if(NOT IPP_LIBRARIES )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(53): set(IPP_LIBRARIES )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ipp_iw )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcore )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcc )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippdc )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippch )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcv )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippe )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippi )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ipps )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippvm )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcore_tl )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcc_tl )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippcv_tl )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(128): list(APPEND IPP_LIBRARIES IPP::ippi_tl )
C:/Program Files (x86)/Intel/oneAPI/ipp/2021.2.0/lib/cmake/ipp/ipp-config.cmake(222): list(REMOVE_DUPLICATES IPP_LIBRARIES )
```
I don’t see anything particularly telling… the variable is set in the “global scope” (i.e. not inside any macro or function), all the script does is set its default value, append multiple times and then remove duplicates.
Thank you very much for the help
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [May 13, 2021, 7:58pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/4 "2021-05-13T19:58:24Z")
> [@LaXiS](#):
>
> It still is not clear to me, the closest thing I found was the `ONEAPI_ROOT` environment variable, but I believe that would only work for `find_package(ONEAPI)`. Not even an entry in the Windows registry. Is there any debug/trace switch that logs the searched directories? Anyway, it’s not a big deal.
CMake 3.19+ has `--debug-find` which should help out with this.
> [@LaXiS](#):
>
> `ipp-config.cmake` explicitly says in its header (full paste [here](https://pastebin.com/j3r67M1N)):
Thanks. The problem is that `list(APPEND)` is in a function. This means that modifications don’t escape the function scope. I recommend filing an issue with IPP upstream to fix this problem.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [May 13, 2021, 8:01pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/5 "2021-05-13T20:01:12Z")
Concrete suggestions:
- rename `add_imported_library_target` to be IPP-specific to avoid conflicts with other packages (such as `ipp_add_imported_library_target`)
- `add_ipp_iw_include_directory` should be mangled too for completeness
- either:
- use `PARENT_SCOPE` at the end of the function to “return” modified values to the caller
- make it a macro (though it’d be nice to also unset lots of those local variables)
- suppress all of those `message()` calls if `QUIET` is provided
---
### Author:  [@LaXiS](https://discourse.cmake.org/u/LaXiS)
#### Post date: [May 13, 2021, 8:46pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/6 "2021-05-13T20:46:58Z")
Thank you very much Ben!
I will file an issue upstream.
Meanwhile, I will just link to the `IPP::` exported targets I need.
Thank you again!
---
### Author:  [@Jossue\_M](https://discourse.cmake.org/u/Jossue_M)
#### Post date: [October 28, 2022, 5:47pm UTC](https://discourse.cmake.org/t/weird-variable-behaviour-with-find-package/3313/7 "2022-10-28T17:47:49Z")
Hello, do you have the link to where this was reported? I am currently having the same issue. IPP\_LIBRARIES are blank.