int a = 0 and int a(0) differences [duplicate]

Answer 1

They're both the same, so there really is no one "best way".

I personally use

int a = 0;

because I find it more clear and it's more widely used in practice.

This applies to your code, where the type is int. For class-types, the first is copy-initialization, whereas the other is direct-initialization, so in that case it would make a difference.

Answer 2

The difference is that () initialization is when you explicitly want it to take one parameter only, e.g:

You can:
int a = 44 + 2;
but you can't:
int a(44) + 2;

Answer 3

In textbooks and literature, one is direct initialization and the other is copy initialization. But, in terms of machine code, there is no difference.

Answer 4

It’s that simple. (Well, almost — there are a few things you can’t name your variables, which we’ll talk about in the next section)

You can also assign values to your variables upon declaration. When we assign values to a variable using the assignment operator (equals sign), it’s called an explicit assignment:

int a= 5; // explicit assignment

You can also assign values to variables using an implicit assignment:

int a(5); // implicit assignment

Even though implicit assignments look a lot like function calls, the compiler keeps track of which names are variables and which are functions so that they can be resolved properly.

Answer 5

From a practical point of view: I would only use int a = 0;.

The int a(0) may be allowed but never used in practice in itself.

---

I think it should not bother you on your level, but let us go further.

Let's say that a is a class, not an int.

class Demo{
public:
  Demo(){}; 
  Demo(int){};
};
Demo a;
Demo b(a);   
Demo c = a;  // clearly expressing copy-init

In this example both b(a) and c=a do the same, and I would discourage you using the fist solution. My reason is, that is looks similar to c(2) which is a construction from arguments.

There are only two valid uses of this bracket-style initialization:

• initialization lists (Demo(int i):data(i){} if Demo has an int data member data),
• new's: Demo *p=new Demo(a); // copy constructing a pointer

Answer 6

int a = 0; and int a(0); make no difference in the machine generated code. They are the same.

Following is the assembly code generated in Visual Studio

int a = 10;   // mov dword ptr [a],0Ah  
int b(10);    // mov dword ptr [b],0Ah