The C runtime system is required for compiling and linking C and C++ programs. C++ programs that use the C++ library functions for complex math and/or standard input/output also require the include elements and modules from the library.
The C runtime system essentially consists of the following components:
Standard include elements for the C library functions
Source programs for the generation of user-specific locales
C runtime modules
The runtime modules contain, among other things, the code for all C library functions, central routines which also permit the implementation of C++ library functions and further routines for implementing the operating system interfaces of C and C++ programs.
The module and entry names of the C runtime system begin with “IC@”, “ICS”, “ICX” or “ICP”.
The C runtime modules are available in a number of versions, which means that they can be fully linked (dynamically or statically), dynamically loaded at runtime and preloaded as shareable in class 4 memory. Not all modules of the C runtime system are designed as shareable and capable of being preloaded. This applies, for example, to the name adapter modules (see "SYSLNK.CRTE library" in section “Libraries of the C runtime system").
These and other components of the C runtime system are stored as library elements in various CRTE libraries. The list below presents the CRTE libraries and associated contents.