LabView 9/27/16 and CSI Ch 10

key points of dataflow

wait to have all input, then execute; reads left to right on operations

Node appearance

want to expand to see all inputs and outputs, expandable node allows you to select btwn diff views

virtual folder

way to organize everything in project

you can't change the address of

what an array points to

Benefits of LabVIEW

wide variety of hardware; built-in analysis libraries

contents of pointer variables may be changed by

addition or subtraction but not multiplication or division

it's sometimes necessary to pass

address of a const item into a pointer

pointer goes through array until address =

address of last element in array; then goes backwards until it points to first element

pointers and dynamic memory

allocation can be used with class objects and structures

dynamic memory allocation

allows program to create own variables "on the fly" can only be done with pointers

address operator isn't needed when

an array's address is assigned to a pointer

pointers can be initialized to

an object's address but object has to exist first

a pointer may be subtracted from

another pointer

control + w

automatically wires everything

an element in an array can be retrieved

by adding subscript to array

pointer can be used as a fxn operator

can change the variable's controls

Waveform

carries data, start time, and dt of a waveform; used in graphs; not x and y, just x and start step

pointer to constant may not be used to

change value it points to; constant pointer may not be changed after initialized

shared folders/auto populating folders

can drag VI's here for it to automatically show up in project

& operator

can retrieve address of variable

array names are

pointer constants-you can't make them point to anything but the array they represent

pointer's data type

pointer to variable

pointer to const points to

constant item-data can't change but pointer can

Icon/Connector pane

useful when making a subVI, can drag onto another VI , helps organize coding

with const pointer, the pointer is

constant, once initialized with the address, it can't point to anything else but can change contents of value

delete

frees up variables pointed to by iptr

what are three parts of a VI

front panel, block diagram, and icon/connector pane

thermocouple measures

voltage

pointers to structures and class variables can be passed to

functions as parameters

control + z

gets rid of broken wires

enum

given options, can make decisions

array[index] =

*(array + index)

control + d

gives indicators and controls (if with constants, control + shift + d)

Language Characteristics

graphical (not text code), data-flow oriented data floating across wires, object oriented

array names without brackets and subscript represents

starting address of array, so it's a pointer

free labels

used for comments make code more understandable

store ____ in a pointer variable after using delete

0; prevents code from inadvertently using pointer to access area of memory that was freed; also prevents errors from occurring if accidentally called a pointer again

short

2 bytes

float/long int

4 bytes

double

8 bytes

Control and Indicators

Controls: inputs; Indicators: outputs; numeric/graph/gauge

context help

control H enables context help

string

control, indicator, can update value of control; constants if want to make a document

express VI

create subVI, run and do step into will get you into subVI; for certain instrument communications; useful if want to go through loop really fast but want to reset display every second

variables may be

created and destroyed while a program is running

we can call the function multiple times with

different arguments for const pointer

red dot

doing something new, like conversion (coercing data)

doorbell

double-sided latch

why would you want to add a fxn to the favorites category in the fxns palette

easier to find

make dependent by

error wire (yellow wire) helps w data flow control

computer hardware can access data at _____ addresses faster than ___ addresses

even; odd

T/F you must create a custom icon to create a subVI

false

when array name dereferenced w a *, it retrieves

first element

Building VI

for functions

Components of a block diagram

for loop, while loops, k structures,

output

has arrow pointing out of it (input has arrow pointing in it)

null pointer

has values at address 0

Wires

helps you see data types passing; broken wire: two data types connected that are incompatible scalars: skinny wires; 1-D and 2-D

++ and --

increment and decrement the pointer variable

*

indicates it's a pointer, allows you to pass from pointer to variable being pointed to and is called the indirection operator

by using *ptr, program directly/indirectly uses the variable after you assign the address of x to ptr

indirectly

when indirection pointer is placed in front of a pointer variable

it dereferences the pointer (work w value the pointer is pointing to)

if program needs new variables

it will request the computer to allocate enough bytes to store

if data type is short then

it would be numbers + 1 * 2(bytes)

clicking mouse

latch (boolean)

block diagram toolbar

lightbulb: enable debugging, show the data run will show actual execution of code; probe: probe data line, lets you see current values; steps: into and over(skip over)

DAQ

measuring physical phenomenon with a computer

why would you use quick drop dialog box instead of the search button and controls

might have error node, sometimes more useful to just type what you want

retain wire values

need this in order to save values when probe the code to see values

pointer to const can also receive the address of a

non-constant item

a pointer is true if it is a

nonzero value

dataflow

not guaranteed order of operation; those without inputs can start before those that need inputs

exception

notifies program that something has gone wrong with operation, default: force executing program to terminate

memory leak

occurs after using a block of memory allocated and forget to free it, remains unavailable until program termination

functions can return

pointers but you must be sure the item the pointer references still exists

dangling

pointing to a memory location that has been freed by delete

data types

properties (modify front panels); boolean data, numeric, strings, enums (number associated w string, like case);

pointer

represents address of a memory location, holds address of some variable

palettes

right click on diagram or front panel, manually look through categories, select for what you want if you don't know what you want, just use quickdrop if you know what you want

char

single byte

memory at address 0 can't be accessed

so assign value 0

what are constants and when should you use them

something you don't want to change; on block diagram, can't interface except w coding

heap

special area of program's memory; when depleted, runtime system will throw an exception to notify that requested memory cannot be allocated

Example finder

specific applications

breakpoints

stops execution there

Dynamic data type

stores info generated or acquired by an Express VI: convert to string or enum

Path

stores location of file or directory; has folder hierarchy inherent in it

Front Panel

string, boolean; includes graphs, can't generate graph on back or block diagram, have to do it here; buttons: run, run continuously, stop, pause(debugging), font, line objects, size objects

control

struct, create own data type, have that be uniform throughout code to give object oriented data approach

->

structure pointer operator; used when want to access a member of a class object through a pointer; used to dereference a pointer to a structure or class

front panel object styles

system control: match windows/mac architecture; classic: very old and simple; silver controls: more 3D looks fancier; modern controls: minimalist approach

use control + space to find

things to do

alternative to passing an argument by reference is

to use a pointer variable

switches

toggles (boolean)

Block Diagram

toolbar, express VIs, wires, where most coding is done in labview

must specify the ______ in pointers

type of data (data that they point to)

when adding a value to pointer

youre adding that value * size of data type referenced by pointer