Is BUILD_SHARED_LIBS an implicit option without being declared as a project option?

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1

According to the docs and this tutorial, it appears that the recommendation is to declare BUILD_SHARED_LIBS as an option().

What precisely is the working status of this flag when it is not declared by the project? It seems like it works and defaults to OFF.

2

It looks like there’s no problem setting it from the command line with -DBUILD_SHARED_LIBS=ON, and if not set then it is implicitly an empty string value (meaning the condition is off).