Using VB Compiler Directives
This Tutorial will allow you to use Visual Basic Compiler Directives such as #IF..#Elseif..#Else..#End If and #Const to create more robust and maintanable code.
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<p class=MsoTitle align=left style='text-align:left'><span style='font-size:
16.0pt;mso-bidi-font-size:12.0pt'>Using VB Compiler Directives<o:p></o:p></span></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>I don’t know how many times I have seen the following code</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt;color:navy'>If</span><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'> DebugMode = true <span style='color:navy'>then</span><o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'><span style='mso-tab-count:1'> </span>Msgbox
“The Variable value is “ & SomeVar, vbokonly, “Debug”<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt;color:navy'>End if</span><span style='color:navy'><o:p></o:p></span></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Or even the following</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><span
style='mso-tab-count:1'> </span><span style='color:#339966'>‘Uncomment
the following to debug this var<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt;
color:#339966'><span style='mso-tab-count:1'> </span>‘Msgbox
“The Variable value is “ & SomeVar, vbokonly, “Debug”</span><span
style='color:lime'><o:p></o:p></span></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal>Many Visual Basic Programmers are not using one of the
powerful features of VB that equate it with other programming languages.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><b>Compiler Directives</b>.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='color:red'>“What are Compiler Directives?”<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:.5in'>Well, Compiler Directives are small
instructions that determine whether or not a piece of code will be included in
the Compile and Link process of creating an executable.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='color:red'>“What are the Compiler Directives to
use in VB?”<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:.5in'>In Visual basic you get the
following</p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:1'> </span>#<span
style='color:navy'>Const</span></p>
<p class=MsoBodyTextIndent>This is private in the module it is defined.<span
style="mso-spacerun: yes"> </span>The Const items are NOT global to the
project only in their specific scope such as a form or class module</p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:1'> </span>#<span
style='color:navy'>If</span></p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:2'> </span>This
is used to evaluate an expression of type #<span style='color:navy'>Const</span>
= n-expression </p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:1'> </span>#<span
style='color:navy'>Elseif</span></p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:2'> </span>This
is used to evaluate an expression of type #<span style='color:navy'>Const</span>
= n-expression within and #<span style='color:navy'>IF</span> block</p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:1'> </span>#<span
style='color:navy'>Else</span></p>
<p class=MsoBodyTextIndent2><span style='mso-tab-count:2'> </span>Code
within this sub-block is compiled if the #<span style='color:navy'>IF</span>
and #<span style='color:navy'>ELSEIF</span> blocks all evaluated to false</p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:1'> </span>#<span
style='color:navy'>End If</span></p>
<p class=MsoNormal style='text-indent:.5in'><span style='mso-tab-count:2'> </span>This
ends the #IF Compiler Directive Block</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='color:red'>“Why would I want to use Compiler
Directives?<span style="mso-spacerun: yes"> </span>I have If Then Statements”<o:p></o:p></span></p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>If you
believe in adding additional code and using additional memory as well as CPU
cycles then Compiler Directives are not for you.<span style="mso-spacerun:
yes"> </span>Not to mention having Debug code or unwanted code in your final
exe simply because you forgot to comment one small line of code.<span
style="mso-spacerun: yes"> </span></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h1>VB Specified Constants</h1>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>Visual
Basic defines some Compiler Constants automatically for you.<span
style="mso-spacerun: yes"> </span>These are:</p>
<p class=MsoNormal><span style='mso-tab-count:2'> </span>Win16<span
style='mso-tab-count:1'> </span>“This indicates that the development
environment is 16-bit”</p>
<p class=MsoNormal><span style='mso-tab-count:2'> </span>Win32<span
style='mso-tab-count:1'> </span>“This indicates that the development
environment is 32-bit”</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h1>How to use Compiler Directives</h1>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>Let’s take
a look at the first set of code we examined.<span style="mso-spacerun: yes">
</span>We notice it is a simple if then determining if the program needs to
show a Message Box with the value of a variable.<span style="mso-spacerun:
yes"> </span>How can we use a Compiler Directive to make this code more
efficient?</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'>- THIS -<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt;color:navy'>If</span><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'> DebugMode = true <span style='color:navy'>then</span><o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'><span style='mso-tab-count:1'> </span>Msgbox
“The Variable value is “ & SomeVar, vbokonly, “Debug”<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt;color:navy'>End if<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'>- CAN BE CHANGED TO -<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'>#<span style='color:navy'>Const</span> DebugMode =
true<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'>#<span style='color:navy'>If</span> DebugMode = true
<span style='color:navy'>then</span><o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'><span style='mso-tab-count:1'> </span>Msgbox
“The Variable value is “ & SomeVar, vbokonly, “Debug”<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='font-size:10.0pt;
mso-bidi-font-size:12.0pt'>#<span style='color:navy'>End If<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal>Notice there was no real change in the code except we used
the #IF directive and ended the statement block with the #END IF statement to
check the value of a special Compiler Variable (which was defined with the
#CONST block)</p>
<p class=MsoNormal>These work the sameway as the If…Else…Elseif…End If
statement we are all used to except for one thing.<span style="mso-spacerun:
yes"> </span>If the condition being tested doesn’t prove true then the code
inside the block WILL NOT be included in the outputted code.<span
style="mso-spacerun: yes"> </span></p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h1>Other uses beside Debug</h1>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>The most
common use for Compiler Directives in other languages such as C and C++ are to
define sets of code for different operating systems and versions.<span
style="mso-spacerun: yes"> </span>We can do the same thing with visual basic.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt;
color:#339966'>‘Programmer needs to determine what kind of code he is trying to
create by defining the<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt;
color:#339966'>‘target OS Version here</span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>Const</span> OSVersion = “Win9X”<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>If</span> OSVersion = "Win9X" <span
style='color:#333399'>Then</span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><span
style='mso-tab-count:1'> </span><span style='color:#339966'>‘Programmer
needs to put specific Windows 95, 98 code here<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>ElseIf</span> OSVersion = "WinNT" <span
style='color:#333399'>Then</span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><span
style='mso-tab-count:1'> </span><span style='color:#339966'>‘Programmer
needs to put specific Windows NT code here<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>ElseIf</span> OSVersion = "Win2K" <span
style='color:#333399'>Then</span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><span
style='mso-tab-count:1'> </span><span style='color:#339966'>‘Programmer
needs to put specific Windows 2000 code here<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>Else</span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'><span
style='mso-tab-count:1'> </span><span style='color:#339966'>‘Programmer
has not defined the OS Version<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt'>#<span
style='color:#333399'>End If<o:p></o:p></span></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt;
color:#333399'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;mso-bidi-font-size:12.0pt;
color:#333399'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<h1>Final Notes</h1>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>An
important thing to remember is that #<span style='color:navy'>Const</span> and
Const variables cannot be interswitched.<span style="mso-spacerun: yes">
</span>If you try to use a #Const variable in place of a const or a const in
place of a #<span style='color:navy'>Const</span> variable VB will give you
Syntax errors.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>Also very
important is to Remember the scope of the #<span style='color:navy'>Const</span>
variable.<span style="mso-spacerun: yes"> </span>It is only within it’s module
like a Form, Module or Class Module.</p>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
<h2>Shawn Elliott</h2>
<p class=MsoNormal><![if !supportEmptyParas]> <![endif]><o:p></o:p></p>
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