To many readers, this might sound the same thing, i.e.
class_type *var = NULL; *var = &some_work; is same as class_type *var = &some_work;
But in actual, it is not. When the declaration and initialization are done at the same step, the compiler calls the copy constructor whereas if done in another step, the compiler calls the default constructor.
To understand this, let’s consider an example:
Example 1: When initialisation is not done at the same step of the declaration
Example 2: When initialization is done with the declaration
prog.cpp: In constructor 'A::A(int)': prog.cpp:8:5: error: uninitialized reference member in 'int&' [-fpermissive] A(int w) ^ prog.cpp:5:10: note: 'int& A::p' should be initialized int& p; ^
Note: In this code, as soon as an object is created compiler will allocate memory to p by running the constructor of class A. Now as we know reference variable needs to be initialized at the same step so it will pop up an error message called “reference member is not initialized” .
As we have seen in code 1, initialisation is not done at the same step of the declaration, but still, our code runs. But in general, it is a rule that “reference member should be initialised and declared at the same step.”
So the answer to the above question is both yes and no.