Standard-Library Components

Imagine writing a program using only the rules of the core language, with no prebuilt pieces to draw on. Every task that involves text, groups of values, output, or running work at the same time would have to be built from the ground up. Experienced C++ programmers almost never work this way. Instead, a body of libraries is developed first, and that body becomes the foundation for everything built afterward.

The difference in effort is large. Most programs are tedious to write in the bare language, while good libraries make nearly any task simple. The C++ standard library is the collection of libraries that forms the foundation for most serious programming work. This article follows one idea through the whole tour: a task is easier when you can match each of its steps to a facility someone has already built and specified for you.

The standard library is not a small add-on. Its specification takes up almost two thirds of the ISO C++ standard, which gives a sense of how much of the language definition is devoted to it. Every complete C++ implementation includes the standard-library facilities described in this tour. You can therefore rely on them wherever a conforming implementation is available.

The diagram makes one boundary easy to see. On one side are the standard facilities, which belong to every complete implementation. On the other side are graphical user interface systems, web interfaces, and database interfaces. Most implementations offer these too, and most application-development environments provide foundation libraries for their own corporate or industrial use. Those interfaces are real and useful, but they are supplied by particular systems and environments, so they are not part of the standard facilities this tour introduces.

The diagram shows why the distinction matters. A program is written against the specification, and it can run on any conforming implementation that supplies the facilities it uses. The same code is meant to work across those implementations. This is the reason the tour's examples are written to be portable: they aim to describe C++ as the standard defines it, not as one particular system happens to provide it.

This tour introduces eight named standard-library types: string, ostream, vector, map, unique_ptr, thread, regex, and complex. Each one stands for a family of facilities that the standard library provides. The goal at this stage is recognition rather than full mastery. You are learning which facility handles which kind of job, not how to use every member of each family.

The first four groupings follow the kinds of work the source names directly: text, groups of values, output, and running work at the same time. string handles text, vector and map handle groups of values, ostream handles output, and thread handles work that runs at the same time. The source does not state what unique_ptr, regex, or complex are for, so this article does not assign them a job. The tour introduces them by name, and their details belong to later, more detailed parts of the course.

The tour suggests a way of thinking: start with a plain task, identify the kind of data involved, and then ask which named facility fits each step. Watch how the program's state grows as you move through the steps. At the start there is nothing stored, and each step adds one more piece of information the program has to keep track of.

Notice the pattern. You did not write any of the four facilities. You identified the kind of data at each step and matched it to a named facility. The programmer's work moved from building storage and output logic from scratch to deciding which facility fits each part of the task.

The standard defines what the library must provide, and much thought went into its design. Much more effort went into its implementations, and much more will continue to go into its maintenance and extension. For that reason, the advice is to explore the standard library and to prefer it over home-made alternatives.