C++ Coding Guidelines

To maintain the code consistent, please use the following conventions. Keep in mind that from here on “good” and “bad” are used to attribute things that would make the coding style match, or not match.


This part of the documentation still a work-in-progess and some old code might not follow these guidlines (which is a bug!).


Use tabs (and configure your IDE to show a size of 8 spaces for them) for writing your code (hopefully we can keep this consistent). If you are modifying someone else’s code, try to keep the coding style similar.

Initialization (=, (), and {})

C++11’s uniform initialization solves some syntactical ambiguity in the language. However, there are cases where ambiguity still exists (for the casual reader, not the compiler) in what is being called and how. Take the following code snipet as an example:

std::vector<int> vec{42};

What does this do? It could create a vector<int> with one hundred default-constructed items. Or it could create a vector<int> with 1 item whose value is 42. Both are theoretically possible.

A great overall description of the issue is Herb Sutter’s GotW post. These guidlines are taken from Abseil’s TotW.

Guidelines for “How do I initialize a variable?”:

  • Use assignment syntax when initializing directly with literal values.

// Good
bool error = false;
std::vector<int> vec = {42};

// Bad
bool error{false};
std::vector<int> vec{42};
  • Use the constructor syntax with parentheses when the initialization is performing some active logic.

// Good
std::vector<int> vec(1, 42);

// Bad
std::vector<int> vec{1, 42}; // makes a vector with two integers
  • Use {} initialization without the = only if the above options don’t compile.

  • Never mix {}s and auto.