Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario descargar pdf (Pagina 53)

A-B VBASIC and Visual BASIC

Appendix B

Differences Between

B–5

DECLARE FUNCTION GetTime$()

DECLARE SUB SetTime$()

The generic name for declaring a procedure’s name and its parameters is

“prototyping”. LXB.EXE creates a prototype for every procedure

encountered whether by the DECLARE statement, the FUNCTION

statement, or the SUB statement.

To allow the user to include files of DECLARE statements without regard to

whether the code for each procedure is also included, LXB will not issue an

error if a procedure is DECLAREd but never defined. Multiple DECLAREs

of the same procedure are permitted but should be identical. Use of a

procedure without its definition will cause an error. Be aware that the

various editors used by Microsoft in their BASICs (QB, QBX, VBDOS,

QBASIC, etc.) usually sort subroutines into alphabetic sequence, which can

ruin any arrangements you may have made to eliminate DECLARE

statements. If prototypes are not present in the source when VBDOS runs a

program, it simply creates them. However, if they are missing when the LIB

compiler is invoked, a compiler error results.

DEFINT letterrange[,letterrange]...

DEFSNG letterrange[,letterrange]...

(DEFDBL letterrange[,letterrange]...)

No longer supported

DEFLNG letterrange[,letterrange]...

DEFSTR letterrange[,letterrange]...

Defines the default type of all variables beginning with the indicated letter

range as either integer, single precision, double precision, long integer, or

string. A-B VBASIC converts any double precision operations to single

precision, so see the details in the “General Restrictions” section. Generally

it is best to define all variables with the following command at the very

beginning of the program, so that all math operations use the fastest form of

arithmetic processing. Variables which need to be floating point can then be

explicitly typed by using the ! or # trailer.

DEFINT A–Z

X! = 123.45 ’Overrides DEFINT statement!

DIM [SHARED] variable[(subscripts)][AS type]...

Declares a variable and allocates storage space. VBDOS will not allow a

fixed length string (nor an array of them) to be passed to a procedure, neither

will A-B VBASIC. So, as an alternative, use TYPE..END TYPE to define a

variable or array of fixed length strings, and pass it instead.

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Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario Pagina 53