Can I use identical names for fields and constructor parameters?

Question

class C {
  T a;
public:
  C(T a): a(a) {;}
};

Is it legal?

Answer 1

Yes it is legal and works on all platforms. It will correctly initialize your member variable a, to the passed in value a.

It is considered by some more clean to name them differently though, but not all. I personally actually use it a lot :)

Initialization lists with the same variable name works because the syntax of an initialization item in an initialization list is as follows:

<member>(<value>)

You can verify what I wrote above by creating a simple program that does this: (It will not compile)

class  A
{

   A(int a)
   : a(5)//<--- try to initialize a non member variable to 5
   {
   }
};

You will get a compiling error something like: A does not have a field named 'a'.

---

On a side note:

One reason why you may not want to use the same member name as parameter name is that you would be more prone to the following:

class  A
{

   A(int myVarriable)
   : myVariable(myVariable)//<--- Bug, there was a typo in the parameter name, myVariable will never be initialized properly
   {
   }
   int myVariable;
};

---

On a side note(2):

One reason why you may want to use the same member name as parameter name is that you would be less prone to the following:

class  A
{

   A(int myVariable_)
   {
     //<-- do something with _myVariable, oops _myVariable wasn't initialized yet
     ...
     _myVariable = myVariable_;
   }
   int _myVariable;
};

This could also happen with large initialization lists and you use _myVariable before initializing it in the initialization list.

Answer 2

Legal: yes, as explained by Brian, compiler knows the name to expect in the initializer list must be a member (or a base class), not anything else.

Good style: most likely not - for a lot of programmers (including you, it seems) the result is not obvious. Using a different name for the parameter will keep the code legal and make it a good style at the same time.

I would prefer writing some of:

class C {
  T a_;
public:
  C(T a): a_(a) {}
};


class C {
 T a;
 public:
 C(T value): a(value) {}
};

Answer 3

if the formal parameter and the member is named same then beware of using this pointer inside constructor to use the member variable

class C {
  T a;
public:
  C(T a): a(a) {
this->a.sort ;//correct
a.sort();//will not affect the actual member variable
}
};