[About The Guide]
Alias assignment--binary (Special)
<idAlias> is the name of the unselected work area to access and must
refer to a work area with a database file in USE.
<nWorkArea> is the number of the unselected work area to access.
<idField> is the name of a field in the specified work area.
<exp> is an expression of any data type to be executed in the
specified work area. If an expression more complicated than a single
field reference is used as the second operand, the expression must be
enclosed in parentheses ( ).
<idVar> is any valid CA-Clipper identifier. Depending on whether
you specify FIELD or MEMVAR, the identifier will be forced to a database
field or memory variable (public or private) reference.
When used with an <idAlias> as the first operand, the alias operator
(->) accesses field information or evaluates an expression in the
indicated work area. The alias operator implicitly SELECTs the
<idAlias> before evaluating the <idField> or <exp> operand. When the
evaluation is complete, the original work area is SELECTed again. An
alias reference can be in an expression or on a line by itself:
Using the alias operator lets you:
. Access information from unselected work areas within
. Access environmental information from unselected work areas
. Access information from unselected work areas in modes such as
REPORT and LABEL FORMs
. Write more compact code
In addition to allowing expression and field evaluation in unselected
work areas, the alias operator makes an explicit reference to a field or
variable using either the FIELD or the MEMVAR keyword aliases. MEMVAR
forces <idVar> to refer to a memory variable name, and FIELD forces it
to reference a database field. These special alias identifiers allow
you to avoid ambiguity when there are conflicts between field and memory
variable names. Remember that a reference to a variable identifier not
prefaced with an alias defaults to a field if there are both field and
memory variables with the same name. To override this, use the (/V)
option when compiling.
In addition to specifying the alias as an identifier, you can access the
target work area using an expression that returns the work area number
if the expression is enclosed by parentheses. This lets you use work
area numbers as handles, which is useful for passing references to work
areas without using macros, aliases, names, etc.
. This example accesses database and work area information in an
unselected work area:
USE Customer NEW
USE Invoices NEW
? Customer->CustName // Result: Bill Smith
? Customer->(RECNO()) // Result: 1
? Customer->(FOUND()) // Result: .F.
? Customer->(City + ", " + State + ;
" " + Zip) // Result: ShadowVille,
// CA 90415
. This example uses a user-defined function (MySeek()) as an
operand of the alias operator for a common operation that normally
requires many more statements:
<process no find>...
FUNCTION MySeek( cSearch )
Note: This example is just an illustration of the alias operator
with a user-defined function. CA-Clipper's DBSEEK() could be used
instead of MySeek().
. This example explicitly references field and memory variables
with the same name:
USE Customer NEW
MEMVAR->CustName = "Bill Smith" // Create a memvar
LOCATE FOR MEMVAR->CustName = FIELD->CustName
. This example uses an expression as a work area handle to
create a work area-independent database operation:
cTable1 := "C:Myfile.dbf"
cTable2 := "D:Myfile.dbf"
USE (cTable1) NEW
hArea1 = SELECT()
USE (cTable2) NEW
hArea2 = SELECT()
DoStuff( hArea1, hArea2 )
FUNCTION DoStuff( hArea1, hArea2 )
LOCAL nCount, nSave
nSave := SELECT()
FOR nCount := 1 TO FCOUNT()
FIELDPUT( nCount, ( hArea2 )-> ;
( FIELDGET( nCount )))
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