Question

I know this is a very basic question, but after a few google searches and clicking on multiple links, I still couldn’t find an answer.

My question is what is the difference between the ” . ” and the ” -> ” in function calling in C++ language?

For example, I have a program with 2 different data structures.
Semaphore aaa;
List bbb;

To use a function on semaphore, I have to do aaa.P();
but on List, I have to do List->append(object);

I don’t quite understand why Semaphore uses .P() whereas List uses ->append()
when semaphore is just a data structure containing an integer and a list.

Answer 1

Use the . operator when you’re accessing members using the object itself, or a reference to the object.

struct Foo
{
  void bar() {}
};

Foo foo;
Foo& fooref = foo;

foo.bar();
fooref.bar();

Use the -> operator when you’re accessing a member via a pointer to the object. Continuing the above example

Foo *fooptr = &foo;

fooptr->bar();
(*fooptr).bar();  // same as preceding line