# Setting \`CMAKE\_CXX\_FLAGS\` within a function
**URL:** https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163
**Category:** Usage
**Created:** [September 29, 2021, 9:22am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163 "2021-09-29T09:22:19Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@mscofield0](https://discourse.cmake.org/u/mscofield0)
#### Post date: [September 29, 2021, 9:22am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/1 "2021-09-29T09:22:19Z")
It seems that `CMAKE_CXX_FLAGS` isn’t being set when I set it inside of a function. I tried checking the contents, it is empty before and after, even within the same function.
These are all things I’ve tried, neither work for me:
```auto
set(${CMAKE_CXX_FLAGS} "${CMAKE_CXX_FLAGS} ${val}")
```
```auto
set(${CMAKE_CXX_FLAGS} "${${CMAKE_CXX_FLAGS}} ${val}")
```
```auto
set(${CMAKE_CXX_FLAGS} "${${CMAKE_CXX_FLAGS}} ${val}" PARENT_SCOPE)
```
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [September 29, 2021, 9:28am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/2 "2021-09-29T09:28:25Z")
You are wrong. To set a variable, use just the variable name, do not expand it:
```cmake
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${val}" PARENT_SCOPE)
```
---
### Author:  [@mscofield0](https://discourse.cmake.org/u/mscofield0)
#### Post date: [September 29, 2021, 9:30am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/3 "2021-09-29T09:30:11Z")
Huh, when is the `${VAR}` syntax used then?
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [September 29, 2021, 9:46am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/4 "2021-09-29T09:46:24Z")
When you pass variable name to a function:
```cmake
function (UPDATE_MY_VAR my_var)
set(${my_var} "my value" PARENT_SCOPE)
endfunction()
update_my_var(VAR_TO_UPDATE)
# here VAR_TO_UPDATE has value "my value"
```
---
### Author:  [@mscofield0](https://discourse.cmake.org/u/mscofield0)
#### Post date: [September 29, 2021, 9:47am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/5 "2021-09-29T09:47:51Z")
Ah, okay. Also, is there a way of forwarding the scope of the variable above two or more functions?
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [September 29, 2021, 10:10am UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/6 "2021-09-29T10:10:59Z")
No. You can only update variables of the parent scope.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [September 29, 2021, 5:50pm UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/7 "2021-09-29T17:50:21Z")
Note that the better solution these days is something like:
```cmake
add_library(buildflags INTERFACE)
target_compile_options(buildflags INTERFACE -Wsome-warning)
# For each target
target_link_libraries(mytgt PRIVATE buildflags)
```
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [September 29, 2021, 6:08pm UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/8 "2021-09-29T18:08:50Z")
@ben.boeckel You mean `target_compile_options`.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [September 29, 2021, 6:33pm UTC](https://discourse.cmake.org/t/setting-cmake-cxx-flags-within-a-function/4163/9 "2021-09-29T18:33:14Z")
Indeed, thanks. I’ve updated the comment.