Coding Style

The coding style for Libre Solar firmware mostly follows the K&R Style.

General rules

  • Indentation with 4 spaces (tabs not allowed)
  • Space before pointer or reference symbols *, & and symbol placed adjacent to name (e.g. int *var)
  • No space before opening brace of function: void foo(int arg);
  • One space after if, for, while and switch statements.
  • Always use curly braces for if and for statements, even for one line.
  • Curly braces for functions start in next line, for flow statements (if, while, switch, for) in the same line.
  • Maximum line length of 100 characters
  • No spaces at end of a line or in an empty line
  • One empty new-line at the end of the file
  • Linux-style line-ending (LF or \n)


  • Classes, structs, typedefs and enums are named using PascalCase or UpperCamelCase. Acronyms are treated as a single word, so a JSON parser is named JsonParser. Custom type name endings with _t are not allowed, as they are reserved for C internal types.
  • Function or method names use snake_case.
  • Global and local variables, parameters and class/struct/union member names also use snake_case.
  • Macros, defines and enum elements are written in UPPER_CASE.
  • File names are always lower case to prevent incompatibilities between different operating systems.
  • Each header file should contain a header guard defines using the file name in upper case letters (e.g. MY_FILE_H) without any underscores _ at the beginning, as names with underscores are reserved for C libraries.


  • C++/C99-style comments // are allowed
  • Expressions behind defines must be enclosed in braces, e.g. #define (3*1034)
  • Comments should be in Doxygen style where applicable.


Header file example.h

#ifndef EXAMPLE_H
#define EXAMPLE_H

 * Character buffer to store strings incl. their maximum size
typdedef struct {
    char *str;      ///< Pointer to string in memory
    size_t size;    ///< Maximum size of buffer
} Buffer

enum MyState {

 * State machine of this nice embedded hardware
 * @param buf Some description here
 * @param foo Meaning of this variable here
void state_machine(Buffer *buf, int foo)

#endif /* EXAMPLE_H */

Implementation file example.c

#include "example.h"

static MyState current_state;

void state_machine(Buffer *buf, int foo)
    switch(current_state) {
        case STATE_ON:
        case STATE_OFF:

    if (buf->str != NULL) {
        // ...
    else {
        // ...

    for (int i = 0; i < 10; i++) {
        // ...