# Get a CMake macro to use in a condition
**URL:** https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761
**Category:** Code
**Tags:** os:windows, gen:ninja
**Created:** [March 24, 2023, 8:55am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761 "2023-03-24T08:55:24Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 24, 2023, 8:55am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/1 "2023-03-24T08:55:24Z")
Hi. I would like to make a choice between 2 files to pass to the compiler options according to a macro defined in compile\_definitions of CMake. How to get this macro in a variable for example and test it please?
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 24, 2023, 2:49pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/2 "2023-03-24T14:49:50Z")
It’s not clear to me what you’re asking. Can you share more details to make it a bit more concrete?
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 24, 2023, 7:49pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/3 "2023-03-24T19:49:02Z")
I am writing a library for 2 different MCUs with 2 different toolchains. I would like to be able to choose macros depending on the MCU I want to use and the appropriate toochain. In order to choose the right file for each toolchain (the linker script in locurence), I would like to be able to retrieve the defined macro in order to choose the right file to use for the right toolchain. I need a way to retrieve the macro I would have defined. There for example i want a way to retrieve and test the first macro (STM32F303). That will be test since it can either it or STM32F411
```auto
target_compile_definitions(
${TARGET_NAME} PRIVATE
-DSTM32F303
-D_DSP_LIB
-D_USE_RTTI
-D_ENABLE_IRQ
)
```
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 24, 2023, 8:59pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/4 "2023-03-24T20:59:32Z")
You can access the compile definitions for a target with `get_property(defines TARGET ${TARGET_NAME} PROPERTY COMPILE_DEFINITIONS)`. Note that this only gets target-specific flags; it will miss things coming in from `CMAKE_C_FLAGS`, directory-scoped `add_definitions`, or usage requirements.
I think a better solution would be something like this:
```cmake
add_library(mcu_stm32f411 INTERFACE)
target_compile_definitions(mcu_stm32f411 INTERFACE STM32F411)
target_link_options(mcu_stm32f411 INTERFACE "SHELL:-flag_for linker_script") # or whatever is needed
```
and similarly for `mcu_stm32f303`. You can then choose which to use per-target without having to consider the other bits.
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 12:01am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/5 "2023-03-25T00:01:17Z")
Thanks for your response. but i dont think it will be suitable for my case. I need something like that
```auto
if(TOOLCHAIN_DIRECTORY PATH_EQUAL "$ENV{TI_TOOLCHAIN_PATH}")
set(LINKER_FILE ${CMAKE_SOURCE_DIR}/device/linker_commands/STM32F303_boot.cmd)
elseif(TOOLCHAIN_DIRECTORY PATH_EQUAL "$ENV{GNU_TOOLCHAIN_PATH}")
set(LINKER_FILE ${CMAKE_SOURCE_DIR}/device/linker_scripts/STM32F303_boot.ld)
endif()
```
This is for the first toolchain depending of the target define STM32F303. Now i want a way to choose another linker files depending of that define. So i want a way to check the entered define and then proceed to the selection of the correct files. The 2 toolchains are differents and dont share the same options
---
### Author:  [@benthevining](https://discourse.cmake.org/u/benthevining)
#### Post date: [March 25, 2023, 12:12am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/6 "2023-03-25T00:12:01Z")
To check if a symbol is defined, you can use `try_compile` with a source file such as:
```cpp
#ifdef YOURSYMBOL
#error WAS_DEFINED
#else
#error NOT_DEFINED
#endif
```
call `try_compile` and then check if the error output includes the string `WAS_DEFINED`.
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 9:57am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/7 "2023-03-25T09:57:58Z")
There is not a way to get only the first macro defined here (STM32F303) and store it in a variable ?
```auto
target_compile_definitions(
${TARGET_NAME} PRIVATE
-DSTM32F303
-D_DSP_LIB
-D_USE_RTTI
-D_ENABLE_IRQ
)
```
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 10:00am UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/8 "2023-03-25T10:00:29Z")
I dont want it to access any of my source code. The symbols are already defined. I choose one of them with a global macro defined in CMake compile\_definitions propriety
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [March 25, 2023, 1:06pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/9 "2023-03-25T13:06:06Z")
`get_property` can only get the whole list. You can use `list()` operations to inspect that list though.
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 1:45pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/10 "2023-03-25T13:45:48Z")
Thanks. So `get_property(defines TARGET ${TARGET_NAME} PROPERTY COMPILE_DEFINITIONS)` will get the list of all compile definitions without -D and will store them in `defines` right ?
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 2:35pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/11 "2023-03-25T14:35:17Z")
I tried many names but didn’t get the right result
```auto
target_compile_definitions(
${TARGET_NAME} PRIVATE
-DSTM32F303
-D_DSP_LIB
-D_USE_RTTI
-D_ENABLE_IRQ
)
get_target_property(DEFINES ${TARGET_NAME} COMPILE_DEFINITIONS)
# Get the first macro defined
list(GET DEFINES 0 DEVICE_DEFINE)
```
and then
```auto
if(DEVICE_DEFINE STREQUAL STM32F303)
set(LINKER_FILE ${CMAKE_SOURCE_DIR}/device/linker_commands/STM32F303_boot.cmd)
elseif(DEVICE_DEFINE STREQUAL STM32G473)
set(LINKER_FILE ${CMAKE_SOURCE_DIR}/device/linker_commands/STM32G473_boot.cmd)
endif()
```
But it didn’t worked. The file was not given to the linker as expected. Am I do something wrong ?
---
### Author:  [@Dr-Itachi](https://discourse.cmake.org/u/Dr-Itachi)
#### Post date: [March 25, 2023, 4:36pm UTC](https://discourse.cmake.org/t/get-a-cmake-macro-to-use-in-a-condition/7761/12 "2023-03-25T16:36:26Z")
get\_property and file solved my problem. Thanks. Now i can build for 2 targets usings 2 differents toolchains without errors