Using the C++ Standard Library Headers

Most C++ programmers meet mathematical functions early, and the functions they use first are usually the ones most people call the standard set. Once a program needs something more specialized, a natural question follows: is there more available, and if so, where does it come from? Suppose you are reading someone else's program and reach a mathematical function you have never seen before. You could search at random through every reference you own, or you could narrow the search in a principled way. This article teaches the second approach.

The three questions form a narrowing path. You begin with the broadest and most familiar region, the standard set of mathematical functions, which is the baseline everything else builds on. If the function is not there, you move to the second region, the small group of additional functions found in the cstdlib header. If it is not there either, you test the third region, the family of special mathematical functions. Those are treated as a separate topic with their own ISO standard, cited in the source as C++Math, 2010.

The cstdlib functions are an addition to the standard picture, not a separate subject. They are a small group of extra mathematical functions gathered into a header that many programmers already know, so they remain part of the general mathematical toolkit. The practical lesson is that cstdlib is one of the places to check, but it is not where most mathematical functions are found. Keeping the cstdlib region small in your mind prevents you from searching it first for everything.

The third region is structurally different from the first two. Special mathematical functions are covered by a separate ISO standard, cited in the source as C++Math, 2010. The practical consequence is that these functions are specified in their own document. A programmer looking for them should not expect them to be described in the same place as the everyday standard functions. This is why the source treats special functions as a distinct topic rather than a simple extension of the header.

The C++ Standard Library is the shared foundation that most C++ programs are built on. It is a set of headers, each of which gives access to a group of related functions and types. Including one header makes that group available to your program. The headers together form the library as a whole.

Real programs almost always build on this shared layer. Nothing significant is built from the bare language alone. Developers first assemble a set of libraries, and those libraries become the foundation for everything written afterward. Each program then carries its own code on top of the common library, so the shared part does not have to be rewritten for every program.

The introductory tour focuses on a handful of commonly used types. Each covers a different kind of job, and seeing them together gives a sense of the library's range. The source names the following facilities, and they are part of every complete implementation of the standard library.

It helps to see the standard library as one layer among several things a complete environment may provide. The standard-library facilities are part of every complete C++ implementation. Most implementations also offer graphical user interface systems, web interfaces, and database interfaces. Application-development environments often add their own foundation libraries for corporate or industrial development and execution. The introductory tour does not describe those systems and libraries, so when you meet one, treat it as outside the standard library.

The source gives three reasons for preferring standard-library facilities to home-made code. Much thought has gone into their design. More thought has gone into their implementations. Substantial effort will continue to go into their maintenance and extension. Each reason is about the life of the code, not only the first day it is written. A home-made version has to be designed, implemented, and maintained by you alone, while a standard facility carries that effort with it.