Working with variables

Variables in CMake are a surprisingly complex subject. Not only are there three categories of variables – normal, cache, and environment – but they also reside in different scopes, with specific rules on how one scope affects the other. Very often, a poor understanding of all these rules becomes a source of bugs and headaches. I recommend you study this section with care and make sure you understand all of concepts before moving on.

Let's start with some key facts about variables in CMake:

• Variable names are case-sensitive and can include almost any character.
• All variables are stored internally as strings, even if some commands can interpret them as values of other data types (even lists!).
• The basic variable manipulation commands are set() and unset(), but there are other commands that can affect variables, such as string() and list().

To set a variable, we simply call set(), providing its name and the value:

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