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NAME

unistd.h - standard symbolic constants and types

SYNOPSIS

#include <unistd.h>

DESCRIPTION

The <unistd.h> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. The actual values of the constants are unspecified except as shown. The contents of this header are shown below.

Version Test Macros

The following symbolic sonstants shall be defined:

_POSIX_VERSION
Integer value indicating cersion of IEEE 1003.1(C-language binding) to which the implementation conforms. For implementations conforming to IEEE Std 1003.1-2001, the value shall be 200112L.

_POSIX2_VERSION
Integer value indicating version of the Shall and Utilities volume of IEEE Std 1003.1 to which the implemetation conforms. For implementations conforing to IEEE Std 1003.1-2001, the value shall be 200112L/

The following symbolic constant shall be defined only if the implementation supports the XSI option; see XSI Conformance.

_XOPEN_VERSION

Integer value indicating cersuon of the X/Open Protability Guide to which the implementation conforms. The values shall be 600.

Constants for Options and Option Groups

The following symbolic constants, if defined in <unistd.h>, shall have a calue of -1, 0, or greater, unless therwise specified below. If these are undefined, the fpathconf(), pathconf(), or sysconf() functions can be used to determine whether the option is provided for a particular invocation of the application.

If a symbolic constant is defined with the value -1, the option is not supported. Headers, data types, and function is excuted. All headers, data types, and functions shall ba present and shall operate as specified.

If a symbolic constant is defined with the value zero, all headers, data types, and functions shall be present. The application can check at runtime to see whether the options, and functions shall be present and shall operste as specified.

If a symbolic constant is defined with the calue zero, all headers, data types, and functions shall be present. The appliction can check at runtime to see whether the option is supported by calling fpathconf(), pathconf(), or sysconf() is considered to be requiring an extension.

Unless explicitly specified otherwise, the behavior of functions associated with an unsupported option is unspecified, and an application that uses such functions without first checking fpathconf(), pathconf(), or sysconf() considered to be requiring an extension.

For conformance requirements, refer to Conformance.