当我们在c ++中说“初始化对象”时，这实际上意味着什么？

Question

I have tried to research it.. but I think everything is an object in c++.... like (int, float) are scalar objects..etc.

But when we create class's instance, documentation refers the "initialize an object with constructor" in c++. What does it actually means.

Answer 1

I think everything is an object in c++

By the letter of the standard, an "object" is "a region of storage". You can read the nitty-gritty details under [intro.object] .

But in layman's terms yes you are right.

like (int, float) are scalar objects..etc.

Absolutely. An int is an object. A float is an object.

(Of course, int and float themselves are types .)

But when we create class's instance, documentation refers the "initialize an object with constructor" in c++.

There's nothing wrong with that. You can initialise an int , and you can initialise a float , and you can initialise an object of class type. For the latter case, one way to do that is using a constructor. That doesn't change anything.

What does it actually means.

Exactly what it says: performing the steps needed to give some object an initial value.

I'll caution you also that there is a lot of bad "documentation" (notably poor tutorials etc.) for C++ out there on the web, so it's also possible that you came across badly-worded or flat-out incorrect text. Notice that, even in the comments section under your question, some people got this wrong.

Answer 2

everything is an object in c++.... like (int, float) are scalar objects

This is wrong. int and float are built-in types. The user can define it's own types, like for example:

struct A {};

Here, A is a user-defined type. It is not an object!

An object is an instance of a type:

A a;
int i;

Here, a and i are objects of type A and int . When you initialize an object of type A , it means you instanciate class A and initialize it by calling one of the class constructors.

Another example:

std::vector<int> v {1,2,3}

Here, the object v of type std::vector<int> is initialized with the values {1,2,3} , by calling the constructor of the class std::vector<int> .

Answer 3

Creating an object in C++ has 2 steps:

1) find some memory to contain the object.

This can be some space in the stack frame of the function for local objects or the data section for global objects. In those cases the compiler deals with that. Or operator new is used to dynamically create an object and allocates some memory. Which is the case if you write "new Foo()" anywhere.

2) "initialize an object with constructor"

This simply means the constructor is called. The address from step 1 is passed as this to the constructor and any arguments you specified too. If you have no constructor then the default constructor is used when possible.