C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 23:
23.1 Is it okay for a non-virtual function of the base class to call a virtual function?
23.2 That last FAQ confuses me. Is it a different strategy from the other ways to use virtual functions? What's going on?
23.3 Should I use protected virtuals instead of public virtuals?
23.4 When should someone use private virtuals?
23.5 When my base class's constructor calls a virtual function on its this object, why doesn't my derived class's override of that virtual function get invoked?
23.6 Okay, but is there a way to simulate that behavior as if dynamic binding worked on the this object within my base class's constructor?
23.7 I'm getting the same mess with destructors: calling a virtual on my this object from my base class's destructor ends up ignoring the override in the derived class; what's going on?
23.8 Should a derived class redefine ("override") a member function that is non-virtual in a base class?
23.9 What's the meaning of, Warning: Derived::f(char) hides Base::f(double)?
23.10 What does it mean that the "virtual table" is an unresolved external?
23.11 How can I set up my class so it won't be inherited from?
23.12 How can I set up my member function so it won't be overridden in a derived class?
[23.1] Is it okay for a non-virtual function of the base class to call a virtual function?

Yes. It's sometimes (not always!) a great idea. For example, suppose all Shape objects have a common algorithm for printing, but this algorithm depends on their area and they all have a potentially different way to compute their area. In this case Shape's area() method would necessarily have to be virtual (probably pure virtual) but Shape::print() could, if we were guaranteed no derived class wanted a different algorithm for printing, be a non-virtual defined in the base class Shape. 

#include "Shape.h"

void Shape::print() const
{
    float a = this->area();  // area() is pure virtual
    ...
}