cpp-style-guide.md

GRPC C++ STYLE GUIDE

Background

Here we document style rules for C++ usage in the gRPC C++ bindings and tests.

General

• The majority of gRPC's C++ requirements are drawn from the [Google C++ style guide] (https://google.github.io/styleguide/cppguide.html)
  • However, gRPC has some additional requirements to maintain [portability] (#portability)
• As in C, layout rules are defined by clang-format, and all code should be passed through clang-format. A (docker-based) script to do so is included in [tools/distrib/clang_format_code.sh] (../tools/distrib/clang_format_code.sh).

Portability Restrictions

gRPC supports a large number of compilers, ranging from those that are missing many key C++11 features to those that have quite detailed analysis. As a result, gRPC compiles with a high level of warnings and treat all warnings as errors. gRPC also forbids the use of some common C++11 constructs. Here are some guidelines, to be extended as needed:

• Do not use range-based for. Expressions of the form

  for (auto& i: vec) {
    // code
  }

  are not allowed and should be replaced with code such as

  for (auto it = vec.begin; it != vec.end(); it++) {
    auto& i = *it;
    // code
  }

• Do not use lambda of any kind (no capture, explicit capture, or default capture). Other C++ functional features such as std::function or std::bind are allowed

• Do not use brace-list initializers.

• Do not compare a pointer to nullptr . This is because gcc 4.4 does not support nullptr directly and gRPC implements a subset of its features in [include/grpc++/impl/codegen/config.h] (../include/grpc++/impl/codegen/config.h). Instead, pointers should be checked for validity using their implicit conversion to bool. In other words, use if (p) rather than if (p != nullptr)

• Do not initialize global/static pointer variables to nullptr. Just let the compiler implicitly initialize them to nullptr (which it will definitely do). The reason is that nullptr is an actual object in our implementation rather than just a constant pointer value, so static/global constructors will be called in a potentially undesirable sequence.

• Do not use final or override as these are not supported by some compilers. Instead use GRPC_FINAL and GRPC_OVERRIDE . These compile down to the traditional C++ forms for compilers that support them but are just elided if the compiler does not support those features.

• In the [include] (../../../tree/master/include/grpc++) and [src] (../../../tree/master/src/cpp) directory trees, you should also not use certain STL objects like std::mutex, std::lock_guard, std::unique_lock, std::nullptr, std::thread . Instead, use grpc::mutex, grpc::lock_guard, etc., which are gRPC implementations of the prominent features of these objects that are not always available. You can use the std versions of those in [test] (../../../tree/master/test/cpp)

• Similarly, in the same directories, do not use std::chrono unless it is guarded by #ifndef GRPC_CXX0X_NO_CHRONO . For platforms that lackstd::chrono, there is a C-language timer called gpr_timespec that can be used instead.

• std::unique_ptr must be used with extreme care in any kind of collection. For example vector<std::unique_ptr> does not work in gcc 4.4 if the vector is constructed to its full size at initialization but does work if elements are added to the vector using functions like push_back. map and other pair-based collections do not work with unique_ptr under gcc 4.4. The issue is that many of these collection implementations assume a copy constructor to be available.

• Don't use std::this_thread . Use gpr_sleep_until for sleeping a thread.

• [Some adjacent character combinations cause problems] (https://en.wikipedia.org/wiki/Digraphs_and_trigraphs#C). If declaring a template against some class relative to the global namespace, <::name will be non-portable. Separate the < from the : and use < ::name.