Coding Style for Apache NimBLE

Apache NimBLE project is part of Apache Mynewt projct and follows its coding style.

Coding Style for Apache Mynewt Core

This document is meant to define the coding style for Apache Mynewt, and all subprojects of Apache Mynewt. This covers C and Assembly coding conventions, only. Other languages (such as Go), have their own coding conventions.


  • All files that are newly written, should have the Apache License clause at the top of them.

  • For files that are copied from another source, but contain an Apache compatible license, the original license header shall be maintained.

  • For more information on applying the Apache license, the definitive source is here:

  • The Apache License clause for the top of files is as follows:

 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.

Whitespace and Braces

  • Code must be indented to 4 spaces, tabs should not be used.

  • Do not add whitespace at the end of a line.

  • Put space after keywords (for, if, return, switch, while).

  • for, else, if, while statements must have braces around their code blocks, i.e., do:

    if (x) {
    } else {


    if (x)
  • Braces for statements must be on the same line as the statement. Good:
    for (i = 0; i < 10; i++) {
        if (i == 5) {
        } else {


    for (i = 0; i < 10; i++)
    { <-- brace must be on same line as for
        if (i == 5) {
        } <-- no new line between else
        else {
  • After a function declaration, the braces should be on a newline, i.e. do:
    static void *
    function(int var1, int var2)


    static void *
    function(int var1, int var2) {

Line Length and Wrap

  • Line length should never exceed 79 columns.

  • When you have to wrap a long statement, put the operator at the end of the line. i.e.:

    if (x &&
        y == 10 &&


    if (x
        && y == 10
        && b)


  • No C++ style comments allowed.

  • When using a single line comment, put it above the line of code that you intend to comment, i.e., do:

    /* check variable */
    if (a) {


    if (a) { /* check variable */
  • All public APIs should be commented with Doxygen style comments describing purpose, parameters and return values. Private APIs need not be documented.

Header files

  • Header files must contain the following structure:

    • Apache License (see above)
    • #ifdef aliasing, to prevent multiple includes
    • #include directives for other required header files
    • #ifdef __cplusplus wrappers to maintain C++ friendly APIs
    • Contents of the header file
  • #ifdef aliasing, shall be in the following format, where the package name is “os” and the file name is “callout.h”:

#ifndef _OS_CALLOUT_H
#define _OS_CALLOUT_H
  • #include directives must happen prior to the cplusplus wrapper.

  • The cplusplus wrapper must have the following format, and precedes any contents of the header file:

#ifdef __cplusplus
#extern "C" {


  • Names of functions, structures and variables must be in all lowercase.

  • Names should be as short as possible, but no shorter.

  • Globally visible names must be prefixed with the name of the module, followed by the ‘_’ character, i.e.:





  • No spaces after function names when calling a function, i.e, do:
    rc = function(a)


    rc = function (a)
  • Arguments to function calls should have spaces between the comma, i.e. do:
    rc = function(a, b)


    rc = function(a,b)
  • The function type must be on a line by itself preceding the function, i.e. do:
    static void *
    function(int var1, int var2)


    static void *function(int var1, int var2)
  • In general, for functions that return values that denote success or error, 0 shall be success, and non-zero shall be the failure code.

Variables and Macros

  • Do not use typedefs for structures. This makes it impossible for applications to use pointers to those structures opaquely.

  • typedef may be used for non-structure types, where it is beneficial to hide or alias the underlying type used (e.g. os_time_t.) Indicate typedefs by applying the _t marker to them.

  • Place all function-local variable definitions at the top of the function body, before any statements.

Compiler Directives

  • Code must compile cleanly with -Wall enabled.