CODEWITHSUNDEEP
c++structmemory-layout
HappyTran
HappyTran

Reputation: 513

C++ Struct is compiled into class?

I am working on C++. I am using MVSV 2010.

When I compile a source code and dump the memory layout of all class with -d1reportAllClassLayout.

For example, I declare struct:

struct my_struct{
    int a;
};

And the memory layout of struct as following:

class my_struct size(4):
    +---
0   | a
    +---

Does it mean that C++ compiler consider struct as same as class at everything? (Expept to default access specifier)

If that, then how about the constructor and deconstructor of struct?

Is there a default constructor and deconstructor of a struct? And it is similar to Class?

Thanks so much for your supports,

Upvotes: 1

Views: 615

Answers (4)

Abhineet
Abhineet

Reputation: 5409

Quoting from Stroustrup's FAQ

A well-designed class presents a clean and simple interface to its users, hiding its representation and saving its users from having to know about that representation. If the representation shouldn't be hidden - say, because users should be able to change any data member any way they like - you can think of that class as "just a plain old data structure"; for example:

struct Pair {
   string name, value; };

A structure is a collection of similar or dissimilar data types. Classes extends the reach of structures by allowing the inclusion of functions within structures. Now, if a structure is just a collection of data-types, you can surely initialize them to some default value just like constructors or else the compiler will do it for you implicitly as mentioned in Vlad's answer but you would not be needing any destructors and there are no destructors by default.

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 311088

In C++ the notion of the class is defined the following way

class-specifier:
    class-head { member-specificationopt}

where class-head in turn is defined like

class-head:
    class-key attribute-specifier-seqopt class-head-name class-virt-specifieropt base-clauseopt
    class-key attribute-specifier-seqopt base-clauseopt

where

class-key:
    class
    struct
    union

Thus a structure is class with class-key struct.

And (C++Standard 12.1 Constructors)

4 A default constructor for a class X is a constructor of class X that can be called without an argument. If there is no user-declared constructor for class X, a constructor having no parameters is implicitly declared as defaulted (8.4). An implicitly-declared default constructor is an inline public member of its class...

As a structure is class and does not have a user-declared constructor then such a constructor is declared implicitly by the compiler.

Upvotes: 1

Glenn Teitelbaum
Glenn Teitelbaum

Reputation: 10343

It could simply mean that d1reportAllClassLayout reports them both the same

Upvotes: 0

Igal S.
Igal S.

Reputation: 14583

In C++ class and struct are (almost) exactly the same. The only difference between them is that the default of class is private and the default of struct is public

Upvotes: 4

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