C Style Guide

This page contains guidelines for writing new C source code for the Paparazzi project.

If you are using Eclipse, you can use Eclipse code style located in the repository (paparazzi_code_profile_eclipse.xml)

Formatting Guide

• remove any trailing white space at the end of lines.
• use 2 spaces for indentation; do NOT use tabs.
• use Unix line endings ('\n'); do NOT use DOS endings ('\r\n')
• limit code length to 100 chars per line
• limit adjacent empty lines to at most two (2).
• remove any trailing empty lines at the end of source files
• do not "comment out" code from the tree; instead, one should either:
  1. remove it entirely (git can retrieve the old version), or
  2. use an #if/#endif block.

Naming Rules

• most identifiers must use lower-case letters (and digits) only.
  • macros should use upper-case letters (and digits) only.

Type Guidelines

• use the types from <inttypes.h>:
  • int8_t, int16_t, int32_t, or int64_t: signed types of specified size
  • uint8_t, uint16_t, uint32_t, or uint64_t: unsigned types of specified size

Functions

• static inline functions should be prefered over macros in most cases:

  /* do NOT define macro-like functions like this... */
  #define CUBE(x) ((x) * (x) * (x))
  /* instead, define the same expression using a C99 inline function */
  static inline int cube(int x) { return x * x * x; }

• Functions should be declared static unless required by other modules
  • define static functions before first usage to avoid forward declarations.
• Functions should have no space between its name and its parameter list:

  int32_t f(int32_t x1, int32_t x2) {
    ...
    int32_t y = f(x1, x2 - x1);
    ...
  }

Switch statements

• specify a default case
• prefer an enum over defines for the different states

  enum state {
    STATE_FOO = 1,
    STATE_BAR = 2
  };
  
  switch (state) {
    case STATE_FOO:
      foo();
      break;
    case STATE_BAR:
      bar();
      break;
    default:
      break;
  }

If statements

• return statement on the new line even for ""simple if"" case

  if (TRUE) {
    return 1;
  }
  
  if (x < other.x) {
    return -1;
  }
  else if (x > other.x) {
    return 1;
  }
  else {
    return 0;
  }

Preprocessor directives

• For conditional compilation use #if instead of #ifdef. Someone might write code like:

  #ifdef USE_FOO
    bar();
  #endif

  Someone else might compile the code with turned-off foo info like:

   gcc stuff.c -DUSE_FOO=0
  

  So use #if not #ifdef to turn a feature on or off. This works fine, and does the right thing, even if USE_FOO is not defined at all (!)

  #if USE_FOO
    bar();
  #endif

• If you really need to test whether a symbol is defined or not, test it with the defined construct.