Certain operating systems do not provide functions which have since
become standardized, or at least common. For example, the Single
Unix Specification Version 2 requires that the basename
function be provided, but an OS which predates that specification
might not have this function. This should not prevent well-written
code from running on such a system.
Similarly, some functions exist only among a particular "flavor"
or "family" of operating systems. As an example, the bzero
function is often not present on systems outside the BSD-derived
family of systems.
Many such functions are provided in libiberty. They are quickly
listed here with little description, as systems which lack them
become less and less common. Each function foo is implemented
in foo.c but not declared in any libiberty header file; more
comments and caveats for each function's implementation are often
available in the source file. Generally, the function can simply
be declared as extern.