1. Introduction

The System Interfaces volume of POSIX.1-2024 describes the interfaces offered to application programs by POSIX-conformant systems.

1.1 Relationship to Other Formal Standards

This volume of POSIX.1-2024 is aligned with the following standards, except where stated otherwise:

ISO C (C17)

ISO/IEC 9899:2018, Programming Languages — C.

Parts of the ISO/IEC 9899:2018 standard (hereinafter referred to as the ISO C standard) are referenced to describe requirements also mandated by this volume of POSIX.1-2024. Some functions and headers included within this volume of POSIX.1-2024 have a version in the ISO C standard; in this case CX markings are added as appropriate to show where the ISO C standard has been extended (see 1.8.1 Codes). Any conflict between this volume of POSIX.1-2024 and the ISO C standard is unintentional, except where stated otherwise.

This volume of POSIX.1-2024 also allows, but does not require, mathematics functions to support IEEE Std 754-1985 and IEEE Std 854-1987.

1.2 Format of Entries

The entries in 3. System Interfaces are based on a common format as follows. The only sections relating to conformance are the SYNOPSIS, DESCRIPTION, RETURN VALUE, and ERRORS sections.

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. If it is necessary to include a header to use this function, the names of such headers are shown, for example:

#include <stdio.h>

DESCRIPTION

This section describes the functionality of the function or header.

RETURN VALUE

This section indicates the possible return values, if any.

If the implementation can detect errors, "successful completion" means that no error has been detected during execution of the function. If the implementation does detect an error, the error is indicated.

For functions where no errors are defined, "successful completion" means that if the implementation checks for errors, no error has been detected. If the implementation can detect errors, and an error is detected, the indicated return value is returned and errno may be set.

ERRORS

This section gives the symbolic names of the error values returned by a function or stored into a variable accessed through the symbol errno if an error occurs.

"No errors are defined" means that error values returned by a function or stored into a variable accessed through the symbol errno, if any, depend on the implementation.

EXAMPLES

This section is informative.

This section gives examples of usage, where appropriate. In the event of conflict between an example and a normative part of this volume of POSIX.1-2024, the normative material is to be taken as correct.

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.1-2024, 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.1-2024 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.