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| All-Resident C Programs |
It
is important to remember that many functions in the C library do not depend
on transient support routines. String functions such as
strcmp
and math functions
such as
cos
are examples of such functions. Complex functions or functions
that interact closely and frequently with the operating system are likely
to be transient. For instance, I/O functions such as
fopen
and signal-handling
functions such as
alarm
are implemented as calls to transient support routines.
These library support routines do not necessarily form
a one-to-one correspondence with the calling function. Often, support routines
can be shared among several callers, and closely related routines can be packaged
together. For example,
fopen
and
afopen
share some support routines,
and all of the support routines for performing I/O to VSAM data sets are packaged
as a unit.
Another important point to remember is that it is not
possible to identify exactly, at link time, the smallest set of support routines
required by a given program. For example, the linker can be relied upon to
include the
strstr
function only if the program contains an external reference
for the function, but it is impossible to determine that no VSAM files will
be opened by examining the external reference for
fopen
. In many cases, even
the programmer cannot predict which support routines will be required.
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