Calling a method from another method in the same class in C++

Question

I wrote a method (that works fine) for a() in a class. I want to write another method in that class that calls the first method so:

void A::a() {
  do_stuff;
}

void A::b() {
  a();
  do_stuff;
}

I suppose I could just rewrite b() so b(A obj) but I don't want to. In java can you do something like this.a().

I want to do obj.b() where obj.a() would be called as a result of obj.b().

oh whoops! I had a different error causing this -- which I just fixed. — devin, Jun 11 '09 at 20:12
If there is a variable in A::a() then how to access that variable in A::b() ? — Darshan, Jan 28 '21 at 07:03

score 71 · Answer 1 · answered Jun 11 '09 at 20:07

71

What you have should work fine. You can use "this" if you want to:

void A::b() {
  this->a();
  do_stuff;
}

or

void A::b() {
  this->A::a();
  do_stuff;
}

or

void A::b() {
  A::a();
  do_stuff;
}

but what you have should also work:

void A::b() {
  a();
  do_stuff;
}

answered Jun 11 '09 at 20:07

Eclipse

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I get an error: `invalid use of 'this' in non-member function` – IgorGanapolsky Jun 03 '16 at 21:03
5

is it a better practice to use `this` when referencing methods/properties of the class? – gen Jul 20 '16 at 12:48
If there is a variable in `A::a()` then how to access that variable in `A::b()` ? – Darshan Jan 28 '21 at 06:57

score 32 · Accepted Answer · answered Jun 11 '09 at 20:05

32

That's exactly what you are doing.

answered Jun 11 '09 at 20:05

rtn

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The answer ^^^ here is not useful; the one below with +44 points is a LOT more insightful. I recommend to change the order in the long run. I will explain why: I came to this here via Google, and the answer was not helping me - but the answer below WITH the syntax made me realize that I simply forgot a (). So the answer below with the +44 points was more helpful for my case, whereas the "what you are doing" comment adds really almost nothing at all to it. – shevy May 05 '20 at 22:13

score 5 · Answer 3 · answered Jun 11 '09 at 20:06

5

It looks like the code you wrote in your block would work just fine. Just make sure you have both the a() and b() methods defined inside your class properly.

answered Jun 11 '09 at 20:06

Tim Rupe

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score 4 · Answer 4 · answered Jun 11 '09 at 20:07

4

What you have written there should work fine. In C++ if you call a within b and both are instance methods of some class A, then you don't need to qualify it. Both a and b are in each others' scope.

answered Jun 11 '09 at 20:07

Todd Gamblin

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score 4 · Answer 5 · answered Jun 12 '09 at 15:08

There's one case in which you might have slightly unexpected results. That is if A::a() is virtual, obj actually has type DerivedFromA, and DerivedFromA::a overrides A::a. In that case, the simple call a(); or the more verbose this->a(); will not call A::a but DerivedFromA::a().

Now, this is probably intended, since class A declared a() to be virtual. But if you really don't mean it, you can ignore the virtual by writing the call either as

void A::b()
{
    A::a(); // or
    this->A::a(); //Both ignore the virtual-ness of a()
}

Calling a method from another method in the same class in C++

5 Answers5