Header file Description First released C Standard <aio.h> Asynchronous input and output Issue 5 <arpa/inet.h> Functions for manipulating numeric IP addresses (part of Berkeley sockets) Issue 6 <assert.h> Verify assumptions Issue 1 ANSI (89) <complex.h> Complex Arithmetic, see C mathematical functions Issue 6 C99 <cpio.h> Magic numbers for the cpio archive format Issue 3 <ctype.h> Character types Issue 1 ANSI (89) <devctl.h> Device control Issue 8 <dirent.h> Allows the opening and listing of directories Issue 2 <dlfcn.h> Dynamic linking Issue 5 <errno.h> Retrieving Error Number Issue 1 ANSI (89) <endian.h> Endianness operations Issue 8 <fcntl.h> File opening, locking and other operations Issue 1 <fenv.h> Floating-Point Environment (FPE), see C mathematical functions Issue 6 C99 <float.h> Floating-point types, see C data types Issue 4 ANSI (89) <fmtmsg.h> Message display structures Issue 4 <fnmatch.h> Filename matching Issue 4 <ftw.h> File tree traversal Issue 1 <glob.h> Pathname "globbing" (pattern-matching) Issue 4 <grp.h> User group information and control Issue 1 <iconv.h> Codeset conversion facility Issue 4 <inttypes.h> Fixed sized integer types, see C data types Issue 5 C99 <iso646.h> Alternative spellings, see C alternative tokens Issue 5 NA1 (95) <langinfo.h> Language information constants – builds on C localization functions Issue 2 <libgen.h> Pathname manipulation Issue 4 <libintl.h> Internationalization Issue 8 <limits.h> Implementation-defined constants, see C data types Issue 1 ANSI (89) <locale.h> Category macros, see C localization functions Issue 3 ANSI (89) <math.h> Mathematical declarations, see C mathematical functions Issue 1 ANSI (89) <monetary.h> String formatting of monetary units Issue 4 <mqueue.h> Message queue Issue 5 <ndbm.h> NDBM database operations Issue 4 <net/if.h> Listing of local network interfaces Issue 6 <netdb.h> Translating protocol and host names into numeric addresses (part of Berkeley sockets) Issue 6 <netinet/in.h> Defines Internet protocol and address family (part of Berkeley sockets) Issue 6 <netinet/tcp.h> Additional TCP control options (part of Berkeley sockets) Issue 6 <nl_types.h> Localization message catalog functions Issue 2 <poll.h> Asynchronous file descriptor multiplexing Issue 4 <pthread.h> Defines an API for creating and manipulating POSIX threads Issue 5 <pwd.h> passwd (user information) access and control Issue 1 <regex.h> Regular expression matching Issue 4 <sched.h> Execution scheduling Issue 5 <search.h> Search tables Issue 1 <semaphore.h> POSIX semaphores Issue 5 <setjmp.h> Stack environment declarations Issue 1 ANSI (89) <signal.h> Signals, see C signal handling Issue 1 ANSI (89) <spawn.h> Process spawning Issue 6 <stdalign.h> Alignment macros Issue 8 C11 <stdarg.h> Handle Variable Argument List Issue 4 ANSI (89) <stdatomic.h> Atomic operations Issue 8 C11 <stdbool.h> Boolean type and values, see C data types Issue 6 C99 <stddef.h> Standard type definitions, see C data types Issue 4 ANSI (89) <stdint.h> Integer types, see C data types Issue 6 C99 <stdio.h> Standard buffered input/output, see C file input/output Issue 1 ANSI (89) <stdlib.h> Standard library definitions, see C standard library Issue 3 ANSI (89) <stdnoreturn.h> The noreturn macro Issue 8 C11 <string.h> Several String Operations, see C string handling Issue 1 ANSI (89) <strings.h> Case-insensitive string comparisons Issue 4 <stropts.h> Stream manipulation, including ioctl Issue 4 <sys/ipc.h> Inter-process communication (IPC) Issue 2 <sys/mman.h> Memory management, including POSIX shared memory and memory mapped files Issue 4 <sys/msg.h> POSIX message queues Issue 2 <sys/resource.h> Resource usage, priorities, and limiting Issue 4 <sys/select.h> Synchronous I/O multiplexing Issue 6 <sys/sem.h> XSI (SysV style) semaphores Issue 2 <sys/shm.h> XSI (SysV style) shared memory Issue 2 <sys/socket.h> Main Berkeley sockets header Issue 6 <sys/stat.h> File information (stat et al.) Issue 1 <sys/statvfs.h> File System information Issue 4 <sys/time.h> Time and date functions and structures Issue 4 <sys/times.h> File access and modification times Issue 1 <sys/types.h> Various data types used elsewhere Issue 1 <sys/uio.h> Vectored I/O operations Issue 4 <sys/un.h> Unix domain sockets Issue 6 <sys/utsname.h> Operating system information, including uname Issue 1 <sys/wait.h> Status of terminated child processes (see wait) Issue 3 <syslog.h> System error logging Issue 4 <tar.h> Magic numbers for the tar archive format Issue 3 <termios.h> Allows terminal I/O interfaces Issue 3 <tgmath.h> Type-Generic Macros, see C mathematical functions Issue 6 C99 <threads.h> ISO C threads Issue 8 C11 <time.h> Type-Generic Macros, see C date and time functions Issue 1 ANSI (89) <trace.h> Tracing of runtime behavior (DEPRECATED) Issue 6 <ucontext.h> manipulate user context (REMOVED in POSIX.1-2008) <ulimit.h> Resource limiting (DEPRECATED in favor of <sys/resource.h>) Issue 1 <unistd.h> Various essential POSIX functions and constants Issue 1 <utime.h> inode access and modification times Issue 3 <utmpx.h> User accounting database functions Issue 4 <wchar.h> Wide-Character Handling, see C string handling Issue 4 NA1 (95) <wctype.h> Wide-Character Classification and Mapping Utilities, see C character classification Issue 5 NA1 (95) <wordexp.h> Word-expansion like the shell would perform Issue 4