c_preprocessor.md

   1 ---
   2 title: C Preprocessor
   3 category: C-like
   4 ---
   5
   6 ### Compiling
   7
   8     $ cpp -P file > outfile
   9
  10 ### Includes
  11
  12     #include "file"
  13
  14 ### Defines
  15
  16     #define FOO
  17     #define FOO "hello"
  18
  19     #undef FOO
  20
  21 ### If
  22
  23     #ifdef DEBUG
  24       console.log('hi');
  25     #elif defined VERBOSE
  26       ...
  27     #else
  28       ...
  29     #endif
  30
  31 ### Error
  32
  33     #if VERSION == 2.0
  34       #error Unsupported
  35       #warning Not really supported
  36     #endif
  37
  38 ### Macro
  39
  40     #define DEG(x) ((x) * 57.29)
  41
  42 ### Token concat
  43
  44     #define DST(name) name##_s name##_t
  45     DST(object);   #=> "object_s object_t;"
  46
  47 ### file and line
  48
  49     #define LOG(msg) console.log(__FILE__, __LINE__, msg)
  50     #=> console.log("file.txt", 3, "hey")