# Generator expression based on user presets
**URL:** https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017
**Category:** Usage
**Created:** [November 22, 2024, 9:50am UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017 "2024-11-22T09:50:56Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@DavidRegan](https://discourse.cmake.org/u/DavidRegan)
#### Post date: [November 22, 2024, 9:50am UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017/1 "2024-11-22T09:50:56Z")
I wish to control target\_compile\_definitions based on user presets so that local mods may be tested. (Want\_Config\_Dump)
In my user preset I’ve added
> ```
> "configurePresets": [
>
> ```
```
{
"name": "config-base-local",
"hidden": true,
"displayName": "base Configuration for local machine",
"description": "Default build using Ninja generator",
"inherits":"config-base",
"cacheVariables": {
"CW_STM32F746_LOCAL_REPO_PATH": "${sourceDir}/../../../",
"STM32CUBEF7_LOCAL_REPO_PATH": "${sourceDir}/../../../",
"CMAKE_BUILD_TYPE": "Debug",
"ARM_TOOLCHAIN_BIN_DIR": "C:/ST/STM32CubeIDE_1.16.0/STM32CubeIDE/plugins/com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.12.3.rel1.win32_1.0.200.202406191623/tools/bin",
"GIT_BASH_CMD": "C:/Program Files/Git/usr/bin/bash",
"CMAKE_EXPORT_COMPILE_COMMANDS": {
"type": "BOOL",
"value": "TRUE"
},
"Use_CW_Local_repo": true,
"Use_ST_Local_repo": true,
"Want_Config_Dump": false
}
},
```
In my CMakeLists.txt I’ve added
> //Applicaton compile definitions
> if (Want\_Config\_Dump)
> set(CFG\_DUMP\_CTRL “-DWANT\_CFG\_DUMP=1”)
> else()
> set(CFG\_DUMP\_CTRL “-DWANT\_CFG\_DUMP=0”)
> endif()
> set(application\_compile\_definitions
> $\<$CONFIG:DEBUG:-DDEBUG\>
> -DUSE\_HAL\_DRIVER
> -DSTM32F746xx
> -DSTM32\_THREAD\_SAFE\_STRATEGY=5
> -DUSES\_RTOS=1
> -DconfigCWSTM32F746\_USE\_CODE\_TRACKPOINTS=0
> -DUSE\_USB\_FS
> -DconfigCWSTM32F746\_USE\_DBG\_TRIGGERS=15
> -DWANT\_ATB\_PBS=1
> -DWANT\_LWIP\_PLATFORM\_OVERRIDES
> -DRELEASE=RELEASEB
> // If WANT\_CFG\_DUMP is non-zero the application will not run the main system loop.
> //This allows the configuration initialisation to be verified
> ${CFG\_DUMP\_CTRL}
> -DLOW\_LEVEL\_IO\_MESSAGES
> -DWANT\_QUEUE\_REGISTRY=1
> -DWANT\_STATMSG\_PRINTOUT=1
> )
This works but I spent a while trying to do this this generator expressions based on Want\_Config\_Dump. Is this possible? I tried a few variations and all said it did not evaluate to a known generator expression
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [November 23, 2024, 7:44pm UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017/2 "2024-11-23T19:44:04Z")
If you are passing these flags to commands like `target_compile_definitions()` and `add_compile_definitions()`, those commands do NOT want the leading `-D` to be included. Older commands like `add_definitions()` do want them, but you shouldn’t be using those old commands anyway. Check the docs of the command(s) you’re using to confirm whether they expect a `-D` or not. This is especially relevant if you’re using generator expressions because the presence of a generator expression bypasses the logic that checks for and removes a stray leading `-D` if an item has it but the command doesn’t want it.
And while I’m here, I’m guessing you probably tried to split your generator expression across multiple lines. See the _Generator Expressions_ section of my [Quoting In CMake](https://crascit.com/2022/01/25/quoting-in-cmake/#h-generator-expressions) article that explains how to do that safely, including examples of how to build up more complicated generator expressions in pieces.
---
### Author:  [@DavidRegan](https://discourse.cmake.org/u/DavidRegan)
#### Post date: [December 9, 2024, 11:56am UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017/3 "2024-12-09T11:56:21Z")
Hi Craig
Sorry for the late response - I got involved in something else. I’m using CMake to control a cross platform build for an embedded system. The -D switch is required in the command line.
I need to have on the command line -DWANT\_CFG\_DUMP=1 or -DWANT\_CFG\_DUMP=0 or nothing.
I think that I’m misunderstang generator expressions. In my user preset file I thought that I could add something like
“Want\_Config\_Dump”: true, in the cacheVariables section
and then evaluate it when generating in CMakeLists.txt with something like
$\
What am I doing wrong
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [December 9, 2024, 8:53pm UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017/4 "2024-12-09T20:53:39Z")
This should get you close:
```auto
$<$:-DWANT_CFG_DUMP=1>
```
The `$` generator expression requires that `xxx` be exactly 0 or 1. No other value is valid. Your `Want_Config_Dump` variable is going to have neither of those values, but will be a boolean-ish string. Wrapping it in `$` converts it to exactly 0 or 1, thereby satisfying the constraint.
---
### Author:  [@DavidRegan](https://discourse.cmake.org/u/DavidRegan)
#### Post date: [December 9, 2024, 9:26pm UTC](https://discourse.cmake.org/t/generator-expression-based-on-user-presets/13017/5 "2024-12-09T21:26:22Z")
Thank you Craig
Just what I wanted