13. Headers

This chapter describes the contents of headers.

Headers contain function prototypes, the definition of symbolic constants, common structures, preprocessor macros, and defined types. Each function in the System Interfaces volume of POSIX.1-2017 specifies the headers that an application shall include in order to use that function. In most cases, only one header is required. These headers are present on an application development system; they need not be present on the target execution system.

Format of Entries

The entries in this chapter are based on a common format as follows. The only sections relating to conformance are the SYNOPSIS and DESCRIPTION.

NAME

This section gives the name or names of the entry and briefly states its purpose.

SYNOPSIS

This section summarizes the use of the entry being described.

DESCRIPTION

This section describes the functionality of the header.

APPLICATION USAGE

This section is informative. This section gives warnings and advice to application developers about the entry. In the event of conflict between warnings and advice and a normative part of this volume of POSIX.1-2017, the normative material is to be taken as correct.

RATIONALE

This section is informative. This section contains historical information concerning the contents of this volume of POSIX.1-2017 and why features were included or discarded by the standard developers.

FUTURE DIRECTIONS

This section is informative. This section provides comments which should be used as a guide to current thinking; there is not necessarily a commitment to adopt these future directions.

SEE ALSO

This section is informative. This section gives references to related information.

CHANGE HISTORY

This section is informative. This section shows the derivation of the entry and any significant changes that have been made to it.