C++ 成员变量指针

Question

I am sure this is a basic question, but I keep receiving memory access errors when I think I am doing this correctly.

What I want to do:

class A{
  string name;
  string date;
}

main{
  A *a = new A();
  a->name= someFunct();
  a->date= someFunct();

  B b;
}
class B{
  A *a;
  printf("%s", a->name); //retrieving data set in main
}

I essentially need to assign some overall settings in one class and want to be able to access those settings throughout the application in the most efficient way.

Answer 1

You're passing a std::string to printf, you need to pass a c string.

printf("%s", a->name.c_str())

Answer 2

In addition to Andreas' answer, you are not initialising *a in B. Just because they are named the same does not mean that they are pointing to the same thing. You need to say something like

b.a = new A();

in your main. Otherwise ba is an empty pointer.

Ie. You need to create an instance of a on your b instance. Alternatively to keep a bit closer to your current code you could do:

int main(char* args[]){
  A *a = new A();
  a->name= someFunct();
  a->date= someFunct();

  B b;
  B.a = a;
  return 0;
}

Answer 3

Maybe this will be useful too:

class A
{
public: //you forgot this
        //defaut is private
   string name;
   string date;
};

int main()
{
   A *a = new A();
   a->name = someFunct();
   a->date = someFunct();

   delete a; //maybe you should do it
}

class B
{
   A *a;

   .....
   printf("%s", a->name.c_str());
   .....
};