Coding Style

This is an overview of the coding conventions we use when writing C++ code for the Open Chemistry projects. The style is based largely on the Qt and KDE styles.

Indentation

• 2 spaces are used for indentation
• Spaces, not tabs!

Line Width

• Keep lines of source code to less than 80 characters wide.

Declaring Variables

• Declare each variable on a separate line
• Avoid abbreviations (e.g. "a", "nmbr") where possible
• Single character variable names are fine for counters, temporary variables etc where the purpose is obvious
• Wait until a variable is needed to declare it, don't keep unused ones around

  // Incorrect
  int nmbr, f;

  // Correct
  int number;
  int result;

• Variables and function names start with a lower case letter, with other words using camel case
• Abbreviated names should be avoided

  // Incorrect
  double Cntr;
  char LIST_DELIMITER = '\t';

  // Correct
  double center;
  char listDelimiter = '\t';

• Class names always start with an upper-case letter
• Public classes should be placed inside the appropriate namespace

Whitespace

• Use blank lines to group statements together where appropriate
• Only use a single blank line
• Always use a single space after a keyword and before a curly brace

// Wrong
if(blah){
  explode();
  return 5;
}

// Correct
if (blah) {
  explode();
  return 5;
}

• For pointers or references, always use a single space between the type and the '*' or '&', but no space between that character and the variable name.

  char *x;
  const std::string &myString;
  const char * const y = "whoah";

• Surround binary operators with spaces
• No space after a cast
• Avoid the use of C-style casts

  // Incorrect
  char* memoryBlock = (char*) malloc(data.size());
  // Correct
  char *memoryBlock = reinterpret_cast<char *>(malloc(data.size()));

Braces

• The left curly brace normally goes on the same line as the start of the statement

  //Incorrect
  if (foo)
  {
    run();
    break;
  }

  // Correct
  if (foo) {
    run();
    break;
  }

• Exception: if this is class declarations and function implementations. The left brace always goes on the start of a line there

  void myFun(const std::string &name)
  {
    std::cout << "Supplied name: " << name << std::endl;
  }

  class Bar
  {
  public:
    Bar();
  };

• Use curly braces when the body of a conditional contains more than one line, and also if a single statement is complex

  // Incorrect
  if (!correct) {
    return false;
  }

  for (int i = 0; i < 42; ++i) {
    var += i;
  }

  // Correct
  if (!correct)
    return false;

  for (int i = 0; i < 42; ++i)
    var += i;

• Exception: Use curly braces if the parent statement does not fit on one line/wraps

  // Correct
  if (!correct || !isValid
      || !aGoodDay) {
    return false;
  }

• Exception: Use curly braces in any if, then, else blocks where any of the elements cover several lines

  // Incorrect
  if (!correct)
    return false;
  else {
    ++counter;
    return true;
  }
  
  // Correct
  if (!correct) {
    return false;
  }
  else {
    ++counter;
    return true;
  }

  // Incorrect
  if (a)
    if (b)
      return true;
    else
      return false;
  
  // Correct
  if (a) {
    if (b)
      return true;
    else
      return false;
  }

• Use curly braces when the body is empty.

  // Incorrect
  while (true);
  
  // Correct
  while (true) {}

Parentheses

• Parentheses should be used to group expressions, and to make the intent clearer

  // Incorrect
  if (a && b || c)

  // Correct
  if ((a && b) || c)

  // Incorrect
  x = a + b & c;

  // Correct
  x = (a + b) & c;

Switch Statements

• The case labels should be in the same column as the switch
• Every case must have a break/return statement at the end, or a comment to indicate the omission
• Exception: Another case follows immediately

  switch (myEnum) {
  case LINE:
    drawLine();
    break;
  case POINT:
  case VERTEX:
    drawDot();
  // Fall through to default.
  default:
    drawDefault();
    break;
  }

Line Breaks

• Keep lines shorter than 80 characters; insert breaks if necessary
• Commas go at the end of a broken line
• Operators go at the beginning of a new line

  // Correct
  if (veryLongExpression()
      && anotherEvenLongerExpression()
      && justWhenYouThoughtItCouldntGetLonger()) {
    doSomething();
  }
  Eigen::Vector3d position(currentPosition.x() + offset,
                           currentPosition.y() + offset,
                           0);

Inheritance and the "virtual" Keyword

• When reimplementing a virtual method, do not put the "virtual" keyword in the header

File Naming

• All file names should be lower-case.
• C++ source files should have a .cpp extension.
• C++ header files should have a .h extension.

General Exception

• As with Qt, and others, feel free to break a rule if it makes your code look bad!