Working on ...
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Type
Objects, references, functions including function template specializations, and expressions have a property called type, which both restricts the operations that are permitted for those entities and provides semantic meaning to the otherwise generic sequences of bits.
Incomplete type
The following types are incomplete types:
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the type void (possibly cv-qualified);
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incompletely-defined object types:
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class type that has been declared (e.g. by forward declaration) but not defined;
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array of unknown bound;
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array of elements of incomplete type;
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enumeration type from the point of declaration until its underlying type is determined.
All other types are complete.
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complete and incomplete type
Where a declaration for a type is in scope, it is either complete or incomplete. Only array types, structure types, union types and enumeration types can be incomplete, because they can be partially declared, with a full declaration coming later. For example, consider these declarations:
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6.11.1 Types (incomplete type)
my note: very clear description for type and incomplete type:
6.11.1 Types
ISO separates C’s types into three distinct sets: function, object, and incomplete. Function types are obvious; object types cover everything else, except when the size of the object is not known. The Standard uses the term “object type” to specify that the designated object must have a known size, but it is important to know that incomplete types other than void also refer to an object.
There are only three variations of incomplete types: void, arrays of unspecified length, and structures and unions with unspecified content. The type void differs from the other two in that it is an incomplete type that cannot be completed, and it serves as a special function return and parameter type..
6.11.2 Completing Incomplete Types
An array type is completed by specifying the array size in a following declaration in the same scope that denotes the same object. When an array without a size is declared and initialized in the same declaration, the array has an incomplete type only between the end of its declarator and the end of its initializer.
An incomplete structure or union type is completed by specifying the content in a following declaration in the same scope for the same tag.
6.11.3 Declarations
Certain declarations can use incomplete types, but others require complete object types. Those declarations that require object types are array elements, members of structures or unions, and objects local to a function. All other declarations permit incomplete types. In particular, the following constructs are permitted:
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Pointers to incomplete types
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Functions returning incomplete types
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Incomplete function parameter types
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typedef names for incomplete types
The function return and parameter types are special. Except for void, an incomplete type used in such a manner must be completed by the time the function is defined or called. A return type of void specifies a function that returns no value, and a single parameter type of void specifies a function that accepts no arguments.
Since array and function parameter types are rewritten to be pointer types, a seemingly incomplete array parameter type is not actually incomplete. The typical declaration of main’s argv, namely, char *argv[], as an unspecified length array of character pointers, is rewritten to be a pointer to character pointers.
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Incomplete Types :: microsoft
An incomplete type is a type that describes an identifier but lacks information needed to determine the size of the identifier. An incomplete type can be:
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A structure type whose members you have not yet specified.
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A union type whose members you have not yet specified.
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An array type whose dimension you have not yet specified.
The void type is an incomplete type that cannot be completed. To complete an incomplete type, specify the missing information. The following examples show how to create and complete the incomplete types...
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Modern C++ Features – Default Initializers for Member Variables
One of the less discussed but nevertheless useful features in C++11 is the possibility to provide initializers for class members right in the class definition..
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Modern C++ Features – std::optional
Sometimes we want to express the state of “nothing meaningful” instead of a value. This is the use case for C++17’s std::optional..
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C++ - Initialization of Static Variables
You are probably reading this because you code in C++. This means that you have battled frustration mastering auto deduction rules or lost your sanity trying to understand why std::initializer_list was considered a good idea. Anyone who has been doing this long enough knows that variable initialization is everything but trivial. It’s a problem too essential to ignore but too challenging to master. Today I’m here to tell you that there is more to it..
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C++ - Inline Variables and Functions
I finally got around to organize the ever-growing collection of notes I’ve gathered in the last years. Scrolling over the 130 notes with the labels programming and cpp, a particular one caught my attention: C++ - Inline Variables and Functions. The note brought back a discussion I had regarding C++17’s newly introduced feature: inline variables, which made me realize how misleading and poorly understood C++’s inline specifier is. In this post I’ll visit the points listed in the note concerning inline: when to use it, how to use it, and what it actually means. Chances are you will be surprised..
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std::variant Doesn't Let Me Sleep
Last month I attended a talk by Juanpe Bolivar: the most valuable values. In his talk he made use of C++17’s new sum type proposal: std::variant. Sum types are objects that can vary their type dynamically. A std::variant is similar to a union: it allocates a fixed portion of memory and reuses it to hold a value of one of several predefined alternative types at a time:
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Understandig Virtual Tables in C++
What does dynamic dispatch mean?
In this context, dispatching just refers to the action of finding the right function to call. In the general case, when you define a method inside a class, the compiler will remember its definition and execute it every time a call to that method is encountered..
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static members
Inside a class definition, the keyword static declares members that are not bound to class instances.
Outside a class definition, it has a different meaning: see storage duration..
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Default initialization
This is the initialization performed when an object is constructed with no initializer..
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Default constructors
A default constructor is a constructor which can be called with no arguments (either defined with an empty parameter list, or with default arguments provided for every parameter). A type with a public default constructor is DefaultConstructible..
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std::optional
Defined in header <optional >
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default constructor
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Default constructors
A default constructor is a constructor which can be called with no arguments (either defined with an empty parameter list, or with default arguments provided for every parameter). A type with a public default constructor is DefaultConstructible.
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How to delete the default constructor?
Sometimes I don't want to provide a default constructor, nor do I want the compiler to provide a system default constructor for my class. In C++ 11 I can do thing like:
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Learn about Deleted Default Constructor in C++
The Constructor in C++ is a function, a method in the class, but it is a ‘special method’ that is automatically called when an object of a class is created. We don’t need to call this function. Whenever a new object of a class is created, the Constructor allows the class to initialize member variables or allocate storage. This is why the name Constructor is given to this special method..
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Explicitly Defaulted and Deleted Functions in C++ 11
What is a Defaulted Function?
Explicitly defaulted function declaration is a new form of function declaration that is introduced into the C++11 standard which allows you to append the ‘=default;’ specifier to the end of a function declaration to declare that function as an explicitly defaulted function. This makes the compiler generate the default implementations for explicitly defaulted functions, which are more efficient than manually programmed function implementations. .
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Explicitly Defaulted and Deleted Functions in C++ 11
clean description.
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Copy Constructor in C++
What is a copy constructor?
A copy constructor is a member function that initializes an object using another object of the same class. A copy constructor has the following general function prototype:
ClassName (const ClassName &old_obj);
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Studied Stuff
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Default arguments
Allows a function to be called without providing one or more trailing arguments.
Indicated by using the following syntax for a parameter in the parameter-list of a function declaration..
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Reference initialization
Binds a reference to an object
in the middle of studying
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Value initialization (since C++03)
This is the initialization performed when an object is constructed with an empty initializer.
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Default initialization
very basic. need good understanding on it..
This is the initialization performed when an object is constructed with no initializer.
Notes
Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-local objects get zero initialized)
References and const scalar objects cannot be default-initialized.
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C++ named requirements: PODType
Specifies that the type is POD (Plain Old Data) type. This means the type is compatible with the types used in the C programming language, that is, can be exchanged with C libraries directly, in its binary form.
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What are POD types in C++?
've come across this term POD-type a few times.
What does it mean?.
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What rules do I have to follow in order to ensure that a C++ type is POD? [duplicate]
I'm writing an interpreter in C++ and I want to make sure that certain C++ data types have a predictable layout for when they are accessed via interpreted code, particularly when using reflection. So for example, I want to make sure that the first data field is always at offset zero from the address of the object. Now, this is trivial for purely POD types. I'm wondering, however, if this can also work with objects that have inheritance or have constructors, as long as I avoid obvious things like virtual functions or multiple inheritance. Is it reasonable to assume that the compiler will layout these types the same way a C compiler would, or would the "unspecified behavior" in the C++ standard be something I would need to worry about?
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What are Aggregates and PODs and how/why are they special?
This FAQ is about Aggregates and PODs and covers the following material:
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What are Aggregates?
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What are PODs (Plain Old Data)?
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How are they related?
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How and why are they special?
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What changes for C++11?
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[26.7] What is a "POD type"?
A type that consists of nothing but Plain Old Data.
A POD type is a C++ type that has an equivalent in C, and that uses the same rules as C uses for initialization, copying, layout, and addressing..
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Trivial, standard-layout, POD, and literal types
The term layout refers to how the members of an object of class, struct or union type are arranged in memory. In some cases, the layout is well-defined by the language specification. But when a class or struct contains certain C++ language features such as virtual base classes, virtual functions, members with different access control, then the compiler is free to choose a layout. That layout may vary depending on what optimizations are being performed and in many cases the object might not even occupy a contiguous area of memory. For example, if a class has virtual functions, all the instances of that class might share a single virtual function table. Such types are very useful, but they also have limitations. Because the layout is undefined they cannot be passed to programs written in other languages, such as C, and because they might be non-contiguous they cannot be reliably copied with fast low-level functions such as memcopy, or serialized over a network..
To enable compilers as well as C++ programs and metaprograms to reason about the suitability of any given type for operations that depend on a particular memory layout, C++14 introduced three categories of simple classes and structs: trivial, standard-layout, and POD or Plain Old Data. The Standard Library has the function templates is_trivial<T >, is_standard_layout <T > and is_pod <T > that determine whether a given type belongs to a given category.
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Using PODs in C++11
In one of my previous posts I tried to show how Boost’s value_initialized can be used to make the usage of PODs (POD = “Plain Old Data”) in C++03 a bit easier. In C++11 this is not necessary. The new language standard provides a number of features that makes the usage of PODs even simpler (although not as simple as one could imagine). Let’s try to explore them..
To be studied ...
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Constructors and member initializer lists
Definition:Constructor is a special non-static member function of a class that is used to initialize objects of its class type.
In the definition of a constructor of a class, member initializer list specifies the initializers for direct and virtual bases and non-static data members. (Not to be confused with std::initializer_list.)
this page contains lot of links for other concepts...
See also
- copy elision
- converting constructor
- copy assignment
- copy constructor
- default constructor
- destructor
- explicit
- initialization
- aggregate initialization
- constant initialization
- copy initialization
- default initialization
- direct initialization
- list initialization
- reference initialization
- value initialization
- zero initialization
- move assignment
- move constructor
- new
Basics- default constructor
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Default constructors
A default constructor is a constructor which can be called with no arguments (either defined with an empty parameter list, or with default arguments provided for every parameter). A type with a public default constructor is DefaultConstructible..
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Converting constructor
A constructor that is not declared with the specifier explicit and which can be called with a single parameter (until C++11) is called a converting constructor.
Unlike explicit constructors, which are only considered during direct initialization (which includes explicit conversions such as static_cast), converting constructors are also considered during copy initialization, as part of user-defined conversion sequence.
It is said that a converting constructor specifies an implicit conversion from the types of its arguments (if any) to the type of its class. Note that non-explicit user-defined conversion function also specifies an implicit conversion.
Implicitly-declared and user-defined non-explicit copy constructors and move constructors are converting constructors.
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Copy constructors
A copy constructor of class T is a non-template constructor whose first parameter is T&, const T&, volatile T&, or const volatile T&, and either there are no other parameters, or the rest of the parameters all have default values.
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Copy assignment operator
A copy assignment operator of class T is a non-template non-static member function with the name operator= that takes exactly one parameter of type T, T&, const T&, volatile T&, or const volatile T&. For a type to be CopyAssignable, it must have a public copy assignment operator..
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explicit specifier
The explicit specifier may only appear within the decl-specifier-seq of the declaration of a constructor or conversion function (since C++11) within its class definition..
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Copy initialization
Initializes an object from another object.
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Direct initialization
Initializes an object from explicit set of constructor arguments..
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Move assignment operator
A move assignment operator of class T is a non-template non-static member function with the name operator= that takes exactly one parameter of type T&&, const T&&, volatile T&&, or const volatile T&&.
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Move constructors
A move constructor of class T is a non-template constructor whose first parameter is T&&, const T&&, volatile T&&, or const volatile T&&, and either there are no other parameters, or the rest of the parameters all have default values..
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new expression
Creates and initializes objects with dynamic storage duration, that is, objects whose lifetime is not necessarily limited by the scope in which they were created.
Tricks
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Easy Trace of Function Entry and All Exits
A simple struct is presented which permits the automatic display to the console of function entry and all exits.
