When Do Preprocessor Directives Execute?

The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements. Thus, preprocessor directives execute before the compiler compiles your program.

Why are preprocessor directives used?

Preprocessor directives, such as #define and #ifdef , are typically used to make source programs easy to change and easy to compile in different execution environments. Directives in the source file tell the preprocessor to take specific actions. ... Preprocessor lines are recognized and carried out before macro expansion.

What is executed by preprocessor in C?

The C preprocessor is a macro processor that is used automatically by the C compiler to transform your program before actual compilation. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs.