Optimized C++

Chapter 6. Optimize Dynamically Allocated Variables

That’s where the money is.

Bank robber Willie Sutton (1901–1980)

This quote was attributed to Sutton as the answer to a reporter’s 1952 question, “Why do you rob banks?” Sutton later denied ever having said it.

Except for the use of less-than-optimal algorithms, the naïve use of dynamically allocated variables is the greatest performance killer in C++ programs. Improving a program’s use of dynamically allocated variables is so often “where the money is” that a developer can be an effective optimizer knowing nothing other than how to reduce calls into the memory manager.

C++ features that use dynamically allocated variables, like standard library containers, smart pointers, and strings, make writing applications in C++ productive. But there is a dark side to this expressive power. When performance matters, new is not your friend.

Lest I start a panic, let me say that the goal in optimizing memory management is not to live an ascetic life free of distraction from the many useful C++ features that use dynamically allocated variables. Rather, the goal is to remove performance-robbing, unneeded calls into the memory manager through skillful use of these same features.

My experience is that removing even one call into the memory manager from a loop or frequently called function is enough to significantly boost performance, and there are generally opportunities to remove many more than one call.

Before talking about ...