# Conditional linker flag

**URL:** https://discourse.cmake.org/t/conditional-linker-flag/6277
**Category:** Code
**Tags:** os:linux
**Created:** [August 16, 2022, 2:16am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277 "2022-08-16T02:16:38Z")
**Posts on this page:** 7
**Page:** 1

<div class="post-metadata">

### Author: ![Progman3K](https://discourse.cmake.org/user_avatar/discourse.cmake.org/progman3k/32/2681_2.png) [@Progman3K](https://discourse.cmake.org/u/Progman3K)
#### Post date: [August 16, 2022, 2:16am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/1 "2022-08-16T02:16:38Z")

</div>

Hi,

I’m a noob.  
I’m trying to pass a specific flag to the linker ONLY if the compiler is GCC 7 or below.

Here is my project structure:

├── CMakeLists.txt  
└── src  
├── CMakeLists.txt  
├── main.cpp  
└── project.h

The top level CMakeLists.txt contains

```auto
project(myproject)

if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17 -Wall -Wunused -g -O0")
    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -DNDEBUG")
elseif(CMAKE_COMPILER_IS_GNUCXX)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17 -Wall -Wunused -g -O0")
    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -DNDEBUG")
endif()

add_subdirectory(src)

```

And the CMakeLists.txt file in the src folder contains

```auto
add_executable(myproject
    main.cpp
)

target_link_libraries(myproject curl)

install (TARGETS myproject DESTINATION bin)

```

The thing is, I’d like the linker options to contain the flag **-lstdc++fs** but only if the version of GCC that ends up being called is inferior to version **8**.

For versions of GCC that are 8 and above the additional linker is not necessary.

I don’t control which version of the compiler will be used.

Is there a way to do this?

Thank you in advance

---

<div class="post-metadata">

### Author: ![benthevining](https://discourse.cmake.org/user_avatar/discourse.cmake.org/benthevining/32/1924_2.png) [@benthevining](https://discourse.cmake.org/u/benthevining)
#### Post date: [August 16, 2022, 2:24am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/2 "2022-08-16T02:24:26Z")

</div>

You can use a generator expressions to achieve this.

Also, prefer to manipulate targets instead of global variables.

Here’s how I would do it:

```cmake
target_link_options (yourTarget PRIVATE $<$<AND:$<CXX_COMPILER_ID:GNU>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,8>>:-lstdc++fs>)

```

---

<div class="post-metadata">

### Author: ![Progman3K](https://discourse.cmake.org/user_avatar/discourse.cmake.org/progman3k/32/2681_2.png) [@Progman3K](https://discourse.cmake.org/u/Progman3K)
#### Post date: [August 16, 2022, 2:39am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/3 "2022-08-16T02:39:00Z")

</div>

I think I’m misunderstanding: It appears to give an error:

```auto
cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_VERBOSE_MAKEFILE=ON ..
-- The C compiler identification is GNU 7.5.0
-- The CXX compiler identification is GNU 7.5.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:15 (target_link_options):
  Unknown CMake command "target_link_options".

-- Configuring incomplete, errors occurred!
See also "/home/user/myproject/files/debug/CMakeFiles/CMakeOutput.log".

```

---

<div class="post-metadata">

### Author: ![benthevining](https://discourse.cmake.org/user_avatar/discourse.cmake.org/benthevining/32/1924_2.png) [@benthevining](https://discourse.cmake.org/u/benthevining)
#### Post date: [August 16, 2022, 2:40am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/4 "2022-08-16T02:40:31Z")

</div>

What version of CMake are you using?

---

<div class="post-metadata">

### Author: ![Progman3K](https://discourse.cmake.org/user_avatar/discourse.cmake.org/progman3k/32/2681_2.png) [@Progman3K](https://discourse.cmake.org/u/Progman3K)
#### Post date: [August 16, 2022, 2:43am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/5 "2022-08-16T02:43:37Z")

</div>

cmake --version  
`cmake version 3.10.2`

---

<div class="post-metadata">

### Author: ![benthevining](https://discourse.cmake.org/user_avatar/discourse.cmake.org/benthevining/32/1924_2.png) [@benthevining](https://discourse.cmake.org/u/benthevining)
#### Post date: [August 16, 2022, 2:44am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/6 "2022-08-16T02:44:17Z")

</div>

The target\_link\_options command was added in version 3.13.

Do you need to support older versions of CMake?

---

<div class="post-metadata">

### Author: ![Progman3K](https://discourse.cmake.org/user_avatar/discourse.cmake.org/progman3k/32/2681_2.png) [@Progman3K](https://discourse.cmake.org/u/Progman3K)
#### Post date: [August 16, 2022, 2:45am UTC](https://discourse.cmake.org/t/conditional-linker-flag/6277/7 "2022-08-16T02:45:13Z")

</div>

I don’t get to choose, it’s a Jenkins installation in this instance and I’m not sure I can upgrade anything  
In fact, if I could upgrade, I’d update its gcc so it would be version 8 or higher and probably not have to add a special option for the linker.