### Author:  [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [February 5, 2020, 5:22pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/1 "2020-02-05T17:22:37Z")
My CMake project builds an executable consisting of C and C++ source files:
```
add_executable(myAP
main.cpp
DpdkSock.c
)
```
I want to specify different compile options for the .cpp and .c files. (For example, compiling the .cpp file requires the -std=c++11 flag, but gcc does not recognise that flag and so it should not be used for the .c file).
How can I achieve this?
(I am using add\_compile\_options() to specify the options).
---
### Author:  [@robert.maynard](https://discourse.cmake.org/u/robert.maynard)
#### Post date: [February 5, 2020, 5:41pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/2 "2020-02-05T17:41:16Z")
You can use generator expressions to state which flags should be used by per language.
My recommendation would be to read Step 10 of the CMake tutorial:
- [https://cmake.org/cmake/help/v3.16/guide/tutorial/index.html#adding-generator-expressions-step-10](https://cmake.org/cmake/help/v3.16/guide/tutorial/index.html#adding-generator-expressions-step-10)
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [February 5, 2020, 5:51pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/3 "2020-02-05T17:51:36Z")
And to manage specifically flag `-std=`, `CMake` have native support of this feature, See [Compile Features](https://cmake.org/cmake/help/v3.16/manual/cmake-compile-features.7.html#manual:cmake-compile-features(7)).
---
### Author:  [@erk](https://discourse.cmake.org/u/erk)
#### Post date: [February 5, 2020, 7:02pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/4 "2020-02-05T19:02:04Z")
This is definitely the way to go. Using [https://cmake.org/cmake/help/v3.16/command/target\_compile\_features.html](https://cmake.org/cmake/help/v3.16/command/target_compile_features.html).
`target_compile_features(myAP PUBLIC cxx_std_11)` will bring appropriate flags on C++ file and not on C file.
if you want to selectively set compilation options on _file_ then you can look at:
[https://cmake.org/cmake/help/v3.16/command/set\_source\_files\_properties.html](https://cmake.org/cmake/help/v3.16/command/set_source_files_properties.html)
---
### Author:  [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [February 6, 2020, 4:02pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/5 "2020-02-06T16:02:41Z")
Thanks for your answers. I am still struggling somewhat. The suggestions worked for -std=c++11, but I also want to enable ‘-pedantic’ for C++ files but not for C. I tried this:
```auto
# Enable pedantic warnings for C++ files but not C files
target_compile_options(ThebeAP PRIVATE
$<$:
-pedantic>)
```
But it seems gcc.exe is still also using -pedantic.
Any thoughts please?
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [February 6, 2020, 4:12pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/6 "2020-02-06T16:12:56Z")
You are not using the right generator expression. `$` asks about compiler id, not the compiler used for files. So, as soon as the C++ compiler is `GNU`, the genex is true.
You have to define options based on compiler used for compiling files:
`$<$:-pedantic>`.
It is clearly explained here: [$\](https://cmake.org/cmake/help/git-master/manual/cmake-generator-expressions.7.html#variable-queries).
---
### Author:  [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [February 6, 2020, 4:24pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/7 "2020-02-06T16:24:25Z")
Thanks. I’m afraid I have a syntax error which I can’t see how to fix from the docs:
```auto
target_compile_options(ThebeAP PRIVATE
$<$:
-pedantic>)
```
```auto
Error evaluating generator expression:
$
Expression did not evaluate to a known generator expression
```
---
### Author:  [@McMartin](https://discourse.cmake.org/u/McMartin)
#### Post date: [February 6, 2020, 5:29pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/8 "2020-02-06T17:29:36Z")
Maybe `COMPILE_LANG_AND_ID` is not available in the CMake version that you are using. It was introduced in CMake 3.15.
However, you can use a combination of regular condition and generator expression (`COMPILE_LANGUAGE` was introduced in CMake 3.3):
```auto
if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
target_compile_options(ThebeAP PRIVATE $<$:-pedantic>)
endif()
```
---
### Author:  [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [February 6, 2020, 5:52pm UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/9 "2020-02-06T17:52:36Z")
@McMartin Thank you. I upgraded to 3.16.4 and COMPILE\_LANG\_AND\_ID then worked fine.
---
### Author:  [@ycdtosa](https://discourse.cmake.org/u/ycdtosa)
#### Post date: [May 10, 2021, 10:57am UTC](https://discourse.cmake.org/t/how-to-specify-different-compile-options-for-c-and-c/583/10 "2021-05-10T10:57:24Z")
This is another alternative using just a combination of generator expressions:
`$<$,$>:-pedantic>`
This is also pointed out in the documentation of [COMPILE\_LANG\_AND\_ID](https://cmake.org/cmake/help/git-master/manual/cmake-generator-expressions.7.html#variable-queries) provided by @marck.chevrier