c++ - Ensure safety while using CRTP -

consider following snippet of code making using of crtp

#include <iostream>  struct alone {     alone() { std::cout << "alone constructor called" << std::endl; }     int me {10}; };  struct dependant {     explicit dependant(const alone& alone)         : ref_alone(alone)     { std::cout << "dependant called alone's me = " << alone.me << std::endl; }     const alone& ref_alone;     void print() { std::cout << ref_alone.me << std::endl; } };  template <typename d> struct base {     base() { std::cout << "base constructor called" << std::endl; }      d* getderived() { return static_cast<d*>(this); }     dependant f { getderived()->alone };     void print() { f.print(); } };  struct derived : base <derived> {     derived() { std::cout << "derived constructor called "  << std::endl; }     alone alone {};     void print() { base::print(); }; };  int main() {     derived d;     d.print(); } 

original link http://coliru.stacked-crooked.com/a/79f8ba2d9c38b965

i have basic question first

• how memory allocation happen when using inheritance? know constructors called base derived, seems when do

  derived d;

  memory equivalent sizeof(d) allocated, , constructors called. understanding correct here? (this explain printing uninitialised member)

• considering above example in mind, suggest/recommend best practices when comes crtp?

memory equivalent sizeof(d) allocated, , constructors called

how else possibly work? can't construct object in memory isn't allocated yet. memory allocation comes before object construction.

considering above example in mind, suggest/recommend best practices when comes crtp?

the standard practices crtp: don't call crtp in constructor/destructor. true of virtual functions. virtuals dynamic polymorphism, while crtp static polymorphism. they're both using same basic mechanism: base class defines interface derived class must implement.

and virtual functions, trying call in constructors/destructors won't mean. difference virtual functions, compiler keep getting undefined behavior. whereas crtp, breakage.

note includes default member initializers, purpose of non-aggregates shorthand constructor initialization lists.