<errno.h>

The <errno.h> include file defines macros that are set to the errno variable. The <errno.h> include file defines macros for values that are used for error reporting in the C library functions and defines the macro errno. An integer value can be assigned to errno, and its value can be tested during runtime. See "Checking the Errno Value" in the ILE C/C++ Programmer's Guide for information about displaying the current errno value.