2.4 RMS Functions

RMS provides a number of functions that create and manipulate files. These functions use RMS data structures to define the characteristics of a file and its records. The data structures are used as indirect arguments to the function call.

The RMS data structures are grouped into four main categories, as follows:

File Access Block (FAB)-Defines the file's characteristics, such as file organization and record format.
Record Access Block (RAB)-Defines the way in which records are processed, such as the record access mode.
Extended Attribute Block (XAB)-Various kinds of extended attribute blocks contain additional file characteristics, such as the definition of keys in an indexed file. Extended attribute blocks are optional.
Name Block (NAM)-Defines all or part of a file specification to be used when an incomplete file specification is given in an OPEN or CREATE operation. Name blocks are optional.

RMS uses these data structures to perform file and record operations. Table 2-1 lists some of the common functions.

Table 2-1 Common RMS Run-Time Processing Functions

Category	Function	Description
File Processing	sys$create	Creates and opens a new file of any organization.
	sys$open	Opens an existing file and initiates file processing.
	sys$close	Terminates file processing and closes the file.
	sys$erase	Deletes a file.
Record Processing	sys$connect	Associates a file access block with a record access block to establish a record access stream; a call to this function is required before any other record-processing function can be used.
	sys$get	Retrieves a record from a file.
	sys$put	Writes a new record to a file.
	sys$update	Rewrites an existing record to a file.
	sys$delete	Deletes a record from a file.
	sys$rewind	Positions the record pointer to the first record in the file.
	sys$disconnect	Disconnects a record access stream.

All RMS functions are directly accessible from DEC C programs. The syntax for any RMS function has the following form:

int sys$name(struct rms_structure *pointer);

In this syntax, name is the name of the RMS function (such as OPEN or CREATE); rms_structure is the name of the structure being used by the function.

The file-processing functions require a pointer to a file access block as an argument; the record-processing functions require a pointer to a record access block as an argument. Since sys$create is a file-processing function, its syntax is as follows:

int sys$create(struct FAB *fab);

These syntax descriptions do not show all the options available when you invoke an RMS function. For a complete description of the RMS calling sequence, see the OpenVMS Record Management Services Reference Manual.

Finally, all the RMS functions return an integer status value. The format of RMS status values follows the standard format described in Chapter 3. Since RMS functions return a 32-bit integer, you do not need to declare the type of an RMS function return before you use it.

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