What is the difference between "option" and "set CACHE BOOL" for a CMake variable?

cmake boolean global-variables cmake-gui
Antonio picture Antonio · Apr 1, 2016 · Viewed 17.7k times · Source

Is there any difference between the following two?

set(FOO true CACHE BOOL "description")

option(FOO "description" ON)

Documentation: set - option

Background: Even if I have been using CMake for a while, I only noticed the option command today and I have therefore always been using set: I was wondering if it is safe/worth to replace the first with the second.

Answer

usr1234567 picture usr1234567 · Apr 1, 2016

In your example, there is no difference. But there can be differences:

  • Option has a default value of OFF.
  • You can make an option dependent on other options with CMakeDependentOption
  • Set accepts types other than BOOL, especially ;-lists.

Additionally, when you use an option you are indicating to your user that it can be set safely. Setting internal variables from the outside might subtly break the script with invalid values.

Related questions

How do I add a linker or compile flag in a CMake file?

I am using the arm-linux-androideabi-g++ compiler. When I try to compile a simple "Hello, World!" program it compiles fine. When I test it by adding a simple exception handling in that code it works too (after adding -fexceptions .. I guess …

Read More
Debug vs Release in CMake

In a GCC compiled project, How do I run CMake for each target type (debug/release)? How do I specify debug and release C/C++ flags using CMake? How do I express that the main executable will be compiled with …

Read More
How to properly add include directories with CMake

About a year ago I asked about header dependencies in CMake. I realized recently that the issue seemed to be that CMake considered those header files to be external to the project. At least, when generating a Code::Blocks project …

Read More