writev Statement

The writev statement writes the value of an expression into the attribute designated in the attribute expression parameter, using the item-ID specified in ID.exp.

Syntax

writev exp ON {file.var ,} ID.exp, ac.exp

Parameter(s)

exp

Expression to write to the specified file.

file.var

File to write to. Contains the item expressed in ID.exp. If omitted, the default file variable is used.

ID.exp

Item to write to. Contains the attribute expressed in ac.exp.

ac.exp

Attribute to write to.

Description

-1 can be used as the value of the attribute count expression. This appends a new attribute to the end of the item.

writev requires that the entire item be read into temporary workspace so that it can be rebuilt with the new attribute value, before it is written back to the file.

A series of writev statements addressing different attributes in the same item can get very slow because the item has to be reread for every writev.

A further problem with writev is that it is not atomic. A writev, although faster, is equivalent to this fragment of BASIC code:

xx<attr> = str

write xx on file,item

Example(s)

writev time() on control.file,’control.list’,3

See Also

Attribute Count Expression

begin work Statement

Default File Variables

File Variable

ID Expression

matread Statement

readv Statement

Statements and Functions

writevu Statement