Java guy reboots with C++ – Trying to understand Memory Mangement

Some random hints if you get started (in my case restarted) with C++ – let me know if I wrote something in wrong in my personal memos:

  1. Use RAII: Resource Acquisition Is Initialization
  2. Use scoped variables which gets destroyed automatically after leaving the block:
    MyClass myVar("Hello Memory");
  3. To use call by reference use the method declaration. But it might be that you are optimizing it when not necessary. Read about Want Speed? Pass by Value.
    void myMethod(MyClass& something)
  4. Understand The Rule of three: If you need to explicitly declare either the destructor, copy constructor or copy assignment operator yourself, you probably need to explicitly declare all three of them. More C++ Idioms
  5. Understand and avoid traps, understand shallow references.
  6. Understandheap vs. stack allocation. E.g. also that heap allocation times are much slower than allocations off the stack.
  7. Use heap allocation when you dynamically want to change memory usage of an object
  8. … or prefer stl (e.g. vector)
  9. … or when an object should be used outside of a method scope:All dynamically allocated memory must be released before the pointer (except smart pointers) pointing to it goes out of scope. So, if the memory is dynamically allocated for a variable within a function, the memory should be released within the function unless a pointer to it is returned or stored by that function.
  10. The = operator in auto_ptr works in a different to normal way!
  11. Read the FAQ or this light-FAQ
  12. oh my: auto_ptr, shared_ptr, smart_ptr, …!!?
  13. Here is a nice compilation of common possible pitfalls.

… but I’m still fighting a bit to understand the memory management problematic:

1. Are there some rules of thumb?


  1. use RAI
  2. if you cannot apply rule 1. use shared_ptr
  3. if you cannot apply rule 1. use new + delete?

2. And how can I solve the problem in C++ when I return a local constructed object (via new) in Java?

E.g. the factory pattern there can look like

public static MyClass createObj() {
  return new MyClass()

3. And how would you e.g. put a vector with a lot of data into a different variable?

Can I rely on the ‘Pass by Value‘ thing which boost performance? Should I use tmpVectorObj.swap(vectorObj2) ?

4. How would you fill a vector within a method?

This is forbidden I think:

// declare vector<Node> vectorObj in the class
void addSomething(string tmp) {
  Node n(tmp);

5. What are the disadvantages of boosts smart pointers?