<p>After creating a instance of a class, can we invoke the constructor explicitly?
For example</p>

<pre><code>class A{
    A(int a)
    {
    }
}

A instance;

instance.A(2);
</code></pre>

<p>Can we do this?</p>

You can use
placement new
, which permits
```
```
new (&instance) A(2);
```
```
However, from your example you'd be calling a constructor on an object twice which is very bad practice. Instead I'd recommend you just do
```
```
A instance(2);
```
```
Placement new is usually only used when you need to pre-allocate the memory (e.g. in a custom memory manager) and construct the object later.