C POSIX library
The C POSIX library is a specification of a C standard library for POSIX systems. It was developed at the same time as the ANSI C standard. Some effort was made to make POSIX compatible with standard C; POSIX includes additional functions to those introduced in standard C.
C POSIX library header files
| Header file | Description | First released |
| ' | Asynchronous input and output | Issue 5 |
| ' | Functions for manipulating numeric IP addresses | Issue 6 |
| ' | Verify assumptions | Issue 1 |
| ' | Complex Arithmetic, see C mathematical functions | Issue 6 |
| ' | Magic numbers for the cpio archive format | Issue 3 |
| ' | Character types | Issue 1 |
| ' | Allows the opening and listing of directories | Issue 2 |
| ' | Dynamic linking | Issue 5 |
| ' | Retrieving Error Number | Issue 1 |
| ' | File opening, locking and other operations | Issue 1 |
| ' | Floating-Point Environment, see C mathematical functions | Issue 6 |
| ' | Floating-point types, see C data types | Issue 4 |
| ' | Message display structures | Issue 4 |
| ' | Filename matching | Issue 4 |
| ' | File tree traversal | Issue 1 |
| ' | Pathname "globbing" | Issue 4 |
| ' | User group information and control | Issue 1 |
| ' | Codeset conversion facility | Issue 4 |
| ' | Fixed sized integer types, see C data types | Issue 5 |
| ' | Alternative spellings, see C alternative tokens | Issue 5 |
| ' | Language information constants – builds on C localization functions | Issue 2 |
| ' | Pathname manipulation | Issue 4 |
| ' | Implementation-defined constants, see C data types | Issue 1 |
| ' | Category macros, see C localization functions | Issue 3 |
| ' | Mathematical declarations, see C mathematical functions | Issue 1 |
| ' | String formatting of monetary units | Issue 4 |
| ' | Message queue | Issue 5 |
| ' | NDBM database operations | Issue 4 |
| ' | Listing of local network interfaces | Issue 6 |
| ' | Translating protocol and host names into numeric addresses | Issue 6 |
| ' | Defines Internet protocol and address family | Issue 6 |
| ' | Additional TCP control options | Issue 6 |
| ' | Localization message catalog functions | Issue 2 |
| ' | Asynchronous file descriptor multiplexing | Issue 4 |
| ' | Defines an API for creating and manipulating POSIX threads | Issue 5 |
| ' | passwd access and control | Issue 1 |
| ' | Regular expression matching | Issue 4 |
| ' | Execution scheduling | Issue 5 |
| ' | Search tables | Issue 1 |
| ' | POSIX semaphores | Issue 5 |
| ' | Stack environment declarations | Issue 1 |
| ' | Signals, see C signal handling | Issue 1 |
| ' | Process spawning | Issue 6 |
| ' | Handle Variable Argument List | Issue 4 |
| ' | Boolean type and values, see C data types | Issue 6 |
| ' | Standard type definitions, see C data types | Issue 4 |
| ' | Integer types, see C data types | Issue 6 |
| ' | Standard buffered input/output, see C file input/output | Issue 1 |
| ' | Standard library definitions, see C standard library | Issue 3 |
| ' | Several String Operations, see C string handling | Issue 1 |
| ' | Case-insensitive string comparisons | Issue 4 |
| ' | Stream manipulation, including ioctl | Issue 4 |
| ' | Inter-process communication | Issue 2 |
| ' | Memory management, including POSIX shared memory and memory mapped files | Issue 4 |
| ' | POSIX message queues | Issue 2 |
| ' | Resource usage, priorities, and limiting | Issue 4 |
| ' | Synchronous I/O multiplexing | Issue 6 |
| ' | XSI semaphores | Issue 2 |
| ' | XSI shared memory | Issue 2 |
| ' | Main Berkeley sockets header | Issue 6 |
| ' | File information | Issue 1 |
| ' | File System information | Issue 4 |
| ' | Time and date functions and structures | Issue 4 |
| ' | File access and modification times | Issue 1 |
| ' | Various data types used elsewhere | Issue 1 |
| ' | Vectored I/O operations | Issue 4 |
| ' | Unix domain sockets | Issue 6 |
| ' | Operating system information, including uname | Issue 1 |
| ' | Status of terminated child processes | Issue 3 |
| ' | System error logging | Issue 4 |
| ' | Magic numbers for the tar archive format | Issue 3 |
| ' | Allows terminal I/O interfaces | Issue 3 |
| ' | Type-Generic Macros, see C mathematical functions | Issue 1 |
| ' | Type-Generic Macros, see C date and time functions | Issue 1 |
| ' | Tracing of runtime behavior | Issue 6 |
| ' | Resource limiting | Issue 1 |
| ' | Various essential POSIX functions and constants | Issue 1 |
| ' | inode access and modification times | Issue 3 |
| ' | User accounting database functions | Issue 4 |
| ' | Wide-Character Handling, see C string handling | Issue 4 |
| ' | Wide-Character Classification and Mapping Utilities, see C character classification | Issue 5 |
| ' | Word-expansion like the shell would perform | Issue 4 |