Information that is needed by several different files or functions is collected into a header file. A header file contains C-language definitions and structures. Centralizing information into a header file facilitates the creation and update of programs. Because #include statements are used to insert header files into a C-language program, header files are often referred to as include files.
Header files define the following functions:
By convention, the names of header files end with .h (dot h). The .h suffix is used by header files that are provided with the operating system; however, the suffix is not required for user-generated header files.
Additional header files are provided with the operating system. Most of these can be found in either the /usr/include directory or the /usr/include/sys directory. Use the pg command to view the contents of a header file.
More information about the following header files is provided in this documentation:
| Item | Description |
|---|---|
| a.out.h | Defines the structure of the standard a.out file. |
| acct.h | Describes the format of the records in the system accounting files. |
| ar.h | Describes the format of an archive file. |
| audit.h | Defines values used by the auditing system as well as the structure of a bin. |
| core.h | Describes the structures created as a result of a core dump. |
| ct_ffdc.h | Provides data types, definitions, and interface prototypes for the First Failure Data Capture (FFDC) C language library interfaces. |
| dirent.h | Describes the format of a file system-independent directory entry. |
| eucioctl.h | Defines ioctl operations and data types for handling EUC code sets. |
| fcntl.h | Defines values for the fcntl and open subroutines. |
| filsys.h | Contains the format of a file system logical volume. |
| flock.h | Defines the file control options. |
| fullstat.h | Describes the data structure returned by the fullstat and ffullstat subroutines. |
| iconv.h | Defines types, macros, and subroutines for character code set conversion. |
| ipc.h | Defines structures used by the subroutines that perform interprocess communications operations. |
| ldr.h | Describes the ld_info data type and loader entry points. |
| libperfstst.h | Describes the structures and constants used by the libperfstat.h API subroutines. |
| limits.h | Defines implementation limits identified by the IEEE POSIX 1003 standard. |
| math.h | Defines math subroutines and constants |
| mode.h | Defines the interpretation of a file mode. |
| msg.h | Defines structures used by the subroutines that perform message queueing operations. |
| mtio.h | Defines the magnetic tape user include file. |
| param.h | Defines certain hardware-dependent parameters. |
| poll.h | Defines the pollfd structure used by the poll subroutine. |
| sem.h | Defines the structures that are used by subroutines that perform semaphore operations. |
| sgtty.h | Defines structures used by the Berkeley terminal interface. |
| shm.h | Defines structures used by the subroutines that perform shared memory operations. |
| spc.h | Defines external interfaces provided by the System Resource Controller (SRC) subroutines. |
| srcobj.h | Defines structures used by the System Resource Controller (SRC) subsystem. |
| stat.h | Describes the data structure returned by the status subroutines. |
| statfs.h | Describes the structure of the statistics returned by the status subroutines. |
| statvfs.h | Describes the structure of the statistics that are returned by the statvfs subroutines and fsatvfs subroutines. |
| systemcfg.h | Defines the _system_configuration structure. |
| tar.h | Defines flags used in the tar archive header. |
| termio.h | Defines structures used by the terminal interface for compatibility of Version 2 of the operating system. |
| termios.h | Defines structures used by the POSIX terminal interface. |
| termiox.h | Defines the structure of the termiox file, which provides the extended terminal interface. |
| trace.h | Defines implementation trace identified by IEEE POSIX 1003. |
| types.h | Defines primitive system data types. |
| unistd.h | Defines POSIX implementation characteristics. |
| utmp.h | Defines the format of certain user and accounting information files. |
| values.h | Defines hardware-dependent values. |
| vmount.h | Describes the structure of a mounted file system. |
| x25sdefs.h | Contains the structures used by the X.25 application programming interface. |