CC, Language topics, Builtin Functions
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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VMS Help CC, Language topics, Builtin Functions *Conan The Librarian (sorry for the slow response - running on an old VAX) |
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Built-in functions allow you to directly access hardware and machine instructions to perform operations that are cumbersome, slow, or impossible in pure C. These functions are very efficient because they are built into the Compaq C compiler. This means that a call to one of these functions does not result in a reference to a function in the C run-time library or in your programs. Instead, the compiler generates the machine instructions necessary to carry out the function directly at the call site. Because most of these built-in functions closely correspond to single VAX or Alpha machine instructions, the result is small, fast code. Some of these functions (such as those that operate on strings or bits) are of general interest. Others (such as the functions dealing with process context) are of interest if you are writing device drivers or other privileged software. Some of the functions are privileged and unavailable to user mode programs. Be sure to include the <builtins.h> header file in your source program to access these built-in functions. Compaq C supports the #pragma builtins preprocessor directive for compatibility with VAX C, but it is not required. Some of the built-in functions have optional arguments or allow a particular argument to have one of many different types. To describe different valid combinations of arguments, the description of each built-in function may list several different prototypes for the function. As long as a call to a built-in function matches one of the prototypes listed, the call is valid. Furthermore, any valid call to a built-in function acts as if the corresponding prototype was in scope, so the compiler performs the argument checking and argument conversions specified by that prototype. The majority of the built-in functions are named after the machine instruction that they generate. For more information on these built-in functions, see the documentation on the corresponding machine instruction. In particular, see that reference for the structure of queue entries manipulated by the queue built-in functions. The Compaq C for OpenVMS VAX built-in functions use enumerated typedefs to define possible return values. We recommend that you use the enumerated types to store and compare return values.
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