c_preprocessor.md

   1 ---
   2 title: C Preprocessor
   3 category: C-like
   4 layout: 2017/sheet
   5 intro: |
   6   Quick reference for the [C macro preprocessor](https://en.m.wikipedia.org/wiki/C_preprocessor), which can be used independent of C/C++.
   7 ---
   8
   9 ## Reference
  10 {: .-three-column}
  11
  12 ### Compiling
  13
  14 ```
  15 $ cpp -P file > outfile
  16 ```
  17
  18 ### Includes
  19
  20 ```
  21 #include "file"
  22 ```
  23
  24 ### Defines
  25
  26 ```
  27 #define FOO
  28 #define FOO "hello"
  29
  30 #undef FOO
  31 ```
  32
  33 ### If
  34
  35 ```
  36 #ifdef DEBUG
  37   console.log('hi');
  38 #elif defined VERBOSE
  39   ...
  40 #else
  41   ...
  42 #endif
  43 ```
  44
  45 ### Error
  46
  47 ```
  48 #if VERSION == 2.0
  49   #error Unsupported
  50   #warning Not really supported
  51 #endif
  52 ```
  53
  54 ### Macro
  55
  56 ```
  57 #define DEG(x) ((x) * 57.29)
  58 ```
  59
  60 ### Token concat
  61
  62 ```
  63 #define DST(name) name##_s name##_t
  64 DST(object);   #=> object_s object_t;
  65 ```
  66
  67 ### Stringification
  68
  69 ```
  70 #define STR(name) #name
  71 char * a = STR(object);   #=> char * a = "object";
  72 ```
  73
  74 ### file and line
  75
  76 ```
  77 #define LOG(msg) console.log(__FILE__, __LINE__, msg)
  78 #=> console.log("file.txt", 3, "hey")
  79 ```