cpp - The C Preprocessor

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

cpp -P inputfile -o outputfile

#include "file"

#define FOO
#define FOO "hello"

#undef FOO

#ifdef DEBUG
  console.log('hi');
#elif defined VERBOSE
  ...
#else
  ...
#endif

#if VERSION == 2.0
  #error Unsupported
  #warning Not really supported
#endif

#define DEG(x) ((x) * 57.29)

#define DST(name) name##_s name##_t
DST(object);   #=> object_s object_t;

#define STR(name) #name
char * a = STR(object);   #=> char * a = "object";

#define LOG(msg) console.log(__FILE__, __LINE__, msg)
#=> console.log("file.txt", 3, "hey")