Avoiding copying data around

The techniques falling under the third point tend to be somehow of a lower-level nature. The first example is avoiding copying data when passing parameters to a function call. A suitable choice of data structure will avoid copying of data as well—just think about an automatically growing vector. In many cases, we can use preallocation techniques to prevent this (such as the reserve() method of std::vector) or choose a different data structure that will better match the intended use case.

Another common case when the copying of data can be a problem is string processing. Just adding two strings together will, in the naive implementation, allocate a new one and copy the contents of the two strings to be joined. And as much of programming contains some string manipulations, this can be a big problem indeed! The remedy for that could be using static string literals or just choosing a better library implementation for strings. 

We'll discuss these themes in Chapter 3, Deep Dive into C++ and Performance, and Chapter 4, Using Data Structures and Algorithms Efficiently.

Another example of this optimization rule is the holy grail of network programming—the zero-copy sending and receiving of data. The idea is that data isn't copied between user buffers and network stack before sending it out. Most modern network hardware supports scatter-gather (also known as vectored I/O), where the data to be sent doesn't have to be provided in a single contiguous buffer but can be made available as a series of separate buffers.

In that way, a user's data doesn't have to be consolidated before sending, sparing us copying of data. The same principle can be applied to software APIs as well; for example, Facebook's recent TSL 1.3 implementation (codename Fizz, open sourced) supports scatter-gather API on library level!