# V1099. Using the function of uninitialized derived class while initializing the base class will lead to undefined behavior.

The analyzer has detected the use of a non-static member function of a derived class while initializing the base class. According to the standard, such code leads to undefined behavior.

Example:

    struct Base
    {
      Base(int);
    };

    struct Derived : public Base
    {
      int FuncFromDerived();
      Derived() : Base(FuncFromDerived()) {}   // <=
    };

The constructor of the 'Derived' structure calls the constructor of the 'Base' base class in the initialization list. At the same time, the result of the 'FuncFromDerived' function, which belongs to the derived structure, is passed as the constructor's argument. When an object of the'Derived' type is created, the initialization will be performed in the following order:

- The 'Derived::FuncFromDerived()' function call;
- The 'Base' constructor call;
- The 'Derived' constructor call.

As a result, a function will be called from a structure that has not been initialized. This violates the standard's rule:

> Member functions (including virtual member functions, [class.virtual]) can be called for an object under construction.

> Similarly, an object under construction can be the operand of the typeid operator ([expr.typeid]) or of a dynamic_cast ([expr.dynamic.cast]).

> However, if these operations are performed in a ctor-initializer (or in a function called directly or indirectly from a ctor-initializer) before all the mem-initializers for base classes have completed, the program has undefined behavior.

This diagnostic is classified as:

CWE-908 CERT-EXP54-CPP

You can look at examples of errors detected by the V1099 diagnostic.