读书笔记：《Effective C++》

Effective C++

GitHub - taeguk/Effective-Cpp-Series: My example and experimental source codes about books of Effective C++ Series, “Effective C++ 3/E” and “Effective Modern C++” by Scott Meyers.

C++ Basic

C++ Union

• C
• Object Oriented C++
• Template C++
• STL
• TR1 - Boost

Using const，enum，inline instead of #define

• constant：using const or enum
  • static int constant can not have in-class definition
    • using enum hack：enum { ConstNum = 5 };
• function macros：using inline function

Using const whenever possible

• bitwise constness: c++ const
• logical constness: mutable field
• call const function in non-const override functin, to avoid code redundant

Make sure init before use

• in construct function:
  • using member init list instead of assignment inside function
  • order by class-field-define-order in init list
• using static object in-function instead of global static object
  • return reference of static local object

Constructor，Destructor， Assignment op

Silent functions in class

• default construction
• default copy construction
• operator=
• destruction
• explicitly use silent functions
  • = default

Explicitly delete silent functions

• make private
• make delete
• move private or delete to a base class and private extend

Virtual destructors in polymorphic

• use virtual destruction in polymorphic base class

Non-throw destructors

• handle exceptions out of destruction
• abort when destruction meet exceptions
• ignore exceptions in destruction

No virtual call in construction and destruction

• in construction or destruction, virtual call can not goto derived class

Operator= return *this

• return *this in operator= to support multi =

Operator= handle self-assignment

• make sure good condition when self-assignment

Deep copy when copy

• copy construction
  • call base copy construction
• operator=
  • call base operator=
• do not call copy construction in operator=, or otherwise

Resource Management

Using resource-managing class

• using RAII class
  • new resource when construction
  • delete resource when destruction
• using smart pointers

Copying resource-managing class

• disable copying: unique ptr
• reference count: shared ptr
• deep copy resource
• move raw resource

Access raw in resource-managing class

• implict cast: use operator(), can be unsafe
• explict cast: use get(), more safer

Same form in new and delete

• new and delete
• new[] and delete[]

Standalone statement when smart pointers

• give new resource to smart pointer in one statement
  • using make_shared, though it will keep reference count when having weak ptr
• construct smart pointer in standalone statement
  • to avoid other part of statement has exceptions

Design

Make interface to easy use

• make new type or enum，static or const value，to make use correctly

Design class as type

• does a new type is really needed
  • consider using non-member to replace a simple derived class

Pass by const reference instead of value

• consider pass by const reference in all place
• pass by value when standard types or function object

Dont return reference

• do not return reference of stack or heap value

Make data member private

• public data member expose the implement details
  • when change public，all user must be changed
  • when change protected，all derived must be changed

Non-member instead of member function

• non-member function can only use public interface, and keep the encapsulation

Non-member function when type conversion

• member function can not conversion the caller’s type, while non-member function can

Non-throw swap

• using std::swap
• using std::swap in member swap
• using member swap in non-member swap

Implementation

Postpone variable definitions

• avoid early returns case no-use variable
• consider re-construction or keep the variable to operator=

Consider casting

• dynamic cast is low efficiency
• C cast:
  • (T)exp
  • T(exp)
• C++ cast:
  • const cast
  • dynamic cast
  • static cast
  • reinterpret cast

Avoid return handles of object internals

• when return handles of object internals, not only the function is const, also the return is const
  • const InternalHandle func() const

Strive for exception safe

• exception safe:
  • when exception, no memery leak, no fake state
• exception safe level:
  • base exception safe: when exception, no memery leak, no fake state
  • force exception safe: when exception, function is full completed or none completed
    • copy and swap
  • nothrow exception safe: no exception

Inlining

• inline is an advice, not a request
• when inline function changed, all dependence file must be re-compile
• when non-inline function changed, only need to re-link

Compilation dependency

• only declare class in classfwd.h, and define those in class.h
  • class declare no change, only change class definition
• handle class: implementation pointer to implementation class
  • handle class no change, only change implementation class
  • additional memory resource management
• interface class: vptr to virtual function
  • base class no change, only change derived class
  • addition virtual table cost

Inheritance and OOP

Public inheritance means is-a

• make sure public inheritance means is-a relationship
  • not has-a relationship
  • not implement-of relationship

Avoid hiding base class through overwrite

• the same name in child class will hide those in base class, though parameters are different
  • using BaseClass::function for not hiding
  • BaseClass::function directly for using once

Interface extend and implementation extend

• pure virtual: interface extend
• impure virtual: interface extand and default implementation
  • if no same name, using default implementation
  • if has same name, hide the default implementation
• non-virtual: implementation extend
  • will hide implementation if the same name in child

Alternative virtual

• template method
  • template method has implementation extend, which can be final
  • call virtual method which has default implementation, also can be overriden
• strategy pattern
  • using function ptr
  • using std::function

Never redefine non-virtual from base class

• base class implementation will be hiden
• also non-virtual function is statically bound, which means, using base class ptr or reference will call the base version

Never redefine default parameters

• virtual function is dynamically bound, while default parameter is statically bound
• which means, virtual function is about the dynamical type, and default parameter is about static type
• alternative implementation: template method
  • non-virtual function to override default parameter
  • call virtuall function to core implementation

Composition means has-a or implement-of

• composition is different from public inheritance
  • has-a
  • implement-of: using public interface to implement new feature
    • ex, using list to implement set

Private inheritance means implement-of

• when implement-of is using protected member, consider private inheritance

Multiple inheritance

• virtual inheritance to handle diamond inheritance
• only use multiple inheritance when implement-of
  • multiple implement interface class
  • multiple implement private inheritance

Template & Generic Programming

Implicit interface and compile-time polymoriphism

• class inheritance and class template both support interface and ploymoriphism
• class inheritance is explicit support
• class template is implicit support

Using typename

• using typename means it is a type not others
  • typename Class::Type_t

Templatized base class

• using template class as base class:
  • template class Child: public Base
• call function in base tempalte class space:
  • just simple func() won’t work
  • force this->func()
  • force using Base::func
  • force Base::func()

Template Parameter

• non-type template parameter change to function parameter, to reduce code size
• type template parameter using shared implementation to reduce code size
  • in base class
  • in non-member function

Member function template

• template Class(U)
  • used in construction
  • used in copy construction or operator=
    • default version is still needed

Non-member function to cast

• member function can not conversion the caller’s type, while non-member function can

Traits class

• using traits class to only handle types in different template specializing

Meta programming

• get result when compiling
  • make sure unit is aligned
  • simplify expression computation
  • implement strategy pattern

New & Delete

• new handler
  • when operator new failed of OOM, will call new handler
  • using set_new_handler to set, usually return abort or exit
• new (std::throw)
  • common new throw bad_alloc when failed
  • nonthrow-new return nullptr when failled
  • though opreator new wont throw, constructor will throw exception either
• why self-defined operator new and delete
  • for debug or stats
  • for long-term program or short-term program, big-block or tiny-block to accelate
    • which standard new and delete are for common use
• self-defined operator new: static void* operator new (std::size_t) throw (std::bad_alloc);
  • handle size is not equal to class size
  • allocate memory in a while loop
  • call new_handler when failed
  • return size-1 when ask for size-0 memory
• self-defined operator delete: static void operator delete (void*) throw();
  • handle size is not equal to class size
• self-defined placement new and delete
  • static void* operator new (std::size_t, void*) throw (std::bad_alloc);
  • static void operator delete (void*, void*) throw();
  • self-define both at the same time
• do not overwrite the standard new and delete
  • explict define standard new and delete in base class
  • add using BaseClass:: operator new/delete in child class if you want to use the standard one

Miscellany

• TR1 是一份规范文档，Boost 则是这个规范的实现，最终会并入 C++ 标准库中