crosses initialization error in switch case statement

Question

I've got the following code:

Class A {
  public:
    A::A(const char* name):
      _name(name)
      {}
    virtual void doSomething();
  private:
    const char* _name;
}

Class B : public A {
  B::B(const char* name):
    A(name)
    {}
  void doSomething() {
    //do something
  }
}

So far so good, but I've experiencing an error crosses initialization of B* newB in the following code:

std::vector<A*> vectorOfAs;

switch (enumType) {
  case enum1 :  
    B* newB = new B("foobar");
    vectorOfAs.push_back(newB);
    break;
  case enum2 :
    C* newC = new C("barfoo");
    vectorOfAs.push_back(newC);
    break;
}

Why the error?

Some background: I want to store pointers of derived classes in a vector for easy searching/iterating. The names are unique so I can iterate through the vector and look for the pointer which points to the object with the right name. When calling a method from a pointed-to object, the inherited one should be called (//do something).

Edit: @François Andrieux: you're right. made (serious) typo. Changed Class B : public B to Class B: public A

Sounds like you have a `goto` or improperly braced `swith` statement. Can you provide a [mcve]? — NathanOliver, Jun 02 '17 at 15:27
`Class B : public B` Seems like you wanted `Class B : public A` ? — François Andrieux, Jun 02 '17 at 15:34
@FrançoisAndrieux Not to mention doSomething should be declared pure virtual in A, and the methods in B are all private. Like Nathan asked for, the actual code that is being compiled would be great. — Mark Loeser, Jun 02 '17 at 15:46
You can have your `std::vector`, and then store derived class objects in it. `B newB = new B("foobar")` instead of `B*` — alejandrogiron, Jun 02 '17 at 16:42
Indeed, the new objects are generated inside a switch/case. I also edited the Class B : public A statement. — BMelis, Jun 02 '17 at 19:39

zdan · Accepted Answer · 2018-03-14T20:11:01.910

newB is in the scope of the switch statement, which makes it available in all switch cases, but won't be initialised in all of them. You should enclose each case in its own local scope (see this answer for more information):

switch (enumType) {
  case enum1 : 
  {
    B* newB = new B("foobar");
    vectorOfAs.push_back(newB);
    break;
  }
  case enum2 :
  {
    C* newC = new C("barfoo");
    vectorOfAs.push_back(newB);
    break;
  }
}

At which point you will get a compiler error in enum2 (thereby exposing a bug), in that you are pushing newB not newC, which is what I assume you intended:

switch (enumType) {
  case enum1 : 
  {
    B* newB = new B("foobar");
    vectorOfAs.push_back(newB);
    break;
  }
  case enum2 :
  {
    C* newC = new C("barfoo");
    vectorOfAs.push_back(newC); // <--
    break;
  }
}

This should work.

Works! I sure would have had to give more info to the previous helpers as NathanOliver was spot on! — BMelis, Jun 02 '17 at 20:07

crosses initialization error in switch case statement

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