This chapter discusses the following topics:
The DEC C compiler is part of the OpenVMS common language environment. This environment defines certain calling procedures and guidelines that allow you to call routines written in different languages from DEC C programs, to call DEC C functions from programs written in other languages, or to call prewritten system routines from DEC C programs. You can call any one of the following routine types from DEC C:
The terms routine, procedure, and function are used throughout this chapter. A routine is a closed, ordered set of instructions that performs one or more specific tasks. Every routine has an entry point (the routine name), and optionally an argument list. Procedures and functions are specific types of routines: a procedure is a routine that does not return a value; a function is a routine that returns a value by assigning that value to the function's identifier.
System routines are prewritten OpenVMS routines that perform common tasks, such as finding the square root of a number or allocating virtual memory. You can call any system routine from your program, provided that DEC C supports the data structures required to call the routine. The system routines used most often are OpenVMS RTL routines and system services. System routines, which are discussed later in this chapter, are documented in detail in the VMS Run-Time Library Routines Volume and the OpenVMS System Services Reference Manual.