What does mean by "inactive" preprocessor block in C?

Question

I found some lines of code, those are dimmed in my preprocessor block of source code in C. My compiler, MS Visual Studio, naming it "inactive preprocessor block". What does this mean, will my compile do not consider these lines of code, and how to make it active block?

Answer 1

An inactive preprocessor block is a block of code that is deactivated because of a preprocessor directive. The simplest example is:

#if 0
//everytyhing here is inactive and will be ignored during compilation
#endif

A more common example would be

#ifdef SOME_VAR
// code
#else
// other code
#endif

In this case either the first or the second block of code will be inactive depending on whether SOME_VAR is defined.