Is it possible to execute a string in VB.Net (like Eval in VBScript)

**Mike Labosh** · Nov 20 '05, 09:10 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

> I need to be able to execute a command that is defined in a string. In[color=blue]
> VBScript, I can do it with the Eval function. How can I do it in VB.Net?[/color]

VB 3.0 used to have this. It was absolutely indispensable!! !!!

There is no way that I have ever heard of to do this in VB.NET, but if you
were to invent a utility object that has a method like this:

Public Function Eval(ByVal expression As String) As Double

and it can handle math, trig, all the operators, etc...

I would buy it from you in a heartbeat.

--
Peace & happy computing,

Mike Labosh, MCSD MCT
Owner, vbSensei.Com
"Escriba coda ergo sum." -- vbSensei

**Tom Shelton** · Nov 20 '05, 09:10 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

On 2003-12-10, Dan <dhartley@somew here.com> wrote:[color=blue]
> I need to be able to execute a command that is defined in a string. In
> VBScript, I can do it with the Eval function. How can I do it in VB.Net?
>
> I need something like:
>
> Dim x As Integer
> Eval("x = 3")
> MsgBox x ' Should show a popup with 3 as the message
>
> I'm in desperate need of this function. There must be something similar in
> VB.Net.
>
> Thanks in advance,
> Dan
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.548 / Virus Database: 341 - Release Date: 12/5/2003
>
>[/color]

Dan,

There is nothing in VB.NET, but there is in JScript.NET. I'm not
exactly sure if this will work for your situation or not, but you can do
something like this:

1. Create a class in JScript -

// JScript Source Code
class EvalClass
{
function Evaluate(expres sion)
{
return eval(expression );
}
}

2. Compile it to a dll (evaluator.dll) :

jsc /target:library evaluator.js

3. Reference the dll in your VB.NET project.

4. Write Code:

Dim ec As New EvalClass()
Dim expr As String = "(10 + 6) / 8"
Dim res As Double = CType(ec.Evalua te(expr), Double)

Console.WriteLi ne("{0} = {1}", expr, res)

You can also pass in bits of JScript code, and have them executed :)
--
Tom Shelton
MVP [Visual Basic]

**Dan** · Nov 20 '05, 09:10 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

Thanks for the help.

It almost does what I want but not quite. It works fine for normal
expressions but runs into problems when the expressions use variables such
as:

Dim x, y As Integer, strExpression As String, ec As New EvalClass()
x = 3
y = 2
strExpression = "x + y"
ec.Evaluate(str Expression)

It throws an error because the x and y variables are not in the
EvalClass.Evalu ate function's scope.

Any other suggestions?

Thanks,
Dan

"Tom Shelton" <tom@mtogden.co m> wrote in message
news:egtWDntvDH A.1088@tk2msftn gp13.phx.gbl...[color=blue]
> On 2003-12-10, Dan <dhartley@somew here.com> wrote:[color=green]
> > I need to be able to execute a command that is defined in a string. In
> > VBScript, I can do it with the Eval function. How can I do it in[/color][/color]
VB.Net?[color=blue][color=green]
> >
> > I need something like:
> >
> > Dim x As Integer
> > Eval("x = 3")
> > MsgBox x ' Should show a popup with 3 as the message
> >
> > I'm in desperate need of this function. There must be something similar[/color][/color]
in[color=blue][color=green]
> > VB.Net.
> >
> > Thanks in advance,
> > Dan
> >
> >
> > ---
> > Outgoing mail is certified Virus Free.
> > Checked by AVG anti-virus system (http://www.grisoft.com).
> > Version: 6.0.548 / Virus Database: 341 - Release Date: 12/5/2003
> >
> >[/color]
>
> Dan,
>
> There is nothing in VB.NET, but there is in JScript.NET. I'm not
> exactly sure if this will work for your situation or not, but you can do
> something like this:
>
> 1. Create a class in JScript -
>
> // JScript Source Code
> class EvalClass
> {
> function Evaluate(expres sion)
> {
> return eval(expression );
> }
> }
>
> 2. Compile it to a dll (evaluator.dll) :
>
> jsc /target:library evaluator.js
>
> 3. Reference the dll in your VB.NET project.
>
> 4. Write Code:
>
> Dim ec As New EvalClass()
> Dim expr As String = "(10 + 6) / 8"
> Dim res As Double = CType(ec.Evalua te(expr), Double)
>
> Console.WriteLi ne("{0} = {1}", expr, res)
>
> You can also pass in bits of JScript code, and have them executed :)
> --
> Tom Shelton
> MVP [Visual Basic][/color]

**Tom Shelton** · Nov 20 '05, 09:10 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

On 2003-12-10, Dan <dhartley@somew here.com> wrote:[color=blue]
> Thanks for the help.
>
> It almost does what I want but not quite. It works fine for normal
> expressions but runs into problems when the expressions use variables such
> as:
>
> Dim x, y As Integer, strExpression As String, ec As New EvalClass()
> x = 3
> y = 2
> strExpression = "x + y"
> ec.Evaluate(str Expression)
>
> It throws an error because the x and y variables are not in the
> EvalClass.Evalu ate function's scope.
>
> Any other suggestions?
>
> Thanks,
> Dan
>[/color]

Hmmm, what about:

Dim strExpression As String
Dim x, y As Integer

x = 3
y = 2

strExpression = String.Format(" {0} + {1}", x, y)
MessageBox.Show (ec.Evaluate(st rExpression).To String())

You may also be able to do something using System.Reflecti on.Emit?
--
Tom Shelton
MVP [Visual Basic]

**Herfried K. Wagner [MVP]** · Nov 20 '05, 09:11 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

* "Dan" <dhartley@somew here.com> scripsit:[color=blue]
> I need to be able to execute a command that is defined in a string. In
> VBScript, I can do it with the Eval function. How can I do it in VB.Net?
>
> I need something like:
>
> Dim x As Integer
> Eval("x = 3")
> MsgBox x ' Should show a popup with 3 as the message
>
> I'm in desperate need of this function. There must be something similar in
> VB.Net.[/color]

Samples:

<http://www.codeproject .com/useritems/evaluator.asp>
<http://www.codeproject .com/csharp/livecodedotnet. asp>

If you have a DevX account:

<http://www.devx.com/codemag/Article/10352/0/page/1>

--
Herfried K. Wagner [MVP]
<http://www.mvps.org/dotnet>

**One Handed Man [ OHM# ]** · Nov 20 '05, 09:11 AM

Re: Is it possible to execute a string in VB.Net (like Eval in VBScript)

I probably would not have thought of that.

Impressed !

:-)

OHM

Tom Shelton wrote:[color=blue]
> On 2003-12-10, Dan <dhartley@somew here.com> wrote:[color=green]
>> I need to be able to execute a command that is defined in a string.
>> In VBScript, I can do it with the Eval function. How can I do it in
>> VB.Net?
>>
>> I need something like:
>>
>> Dim x As Integer
>> Eval("x = 3")
>> MsgBox x ' Should show a popup with 3 as the message
>>
>> I'm in desperate need of this function. There must be something
>> similar in VB.Net.
>>
>> Thanks in advance,
>> Dan
>>
>>
>> ---
>> Outgoing mail is certified Virus Free.
>> Checked by AVG anti-virus system (http://www.grisoft.com).
>> Version: 6.0.548 / Virus Database: 341 - Release Date: 12/5/2003
>>
>>[/color]
>
> Dan,
>
> There is nothing in VB.NET, but there is in JScript.NET. I'm not
> exactly sure if this will work for your situation or not, but you can
> do something like this:
>
> 1. Create a class in JScript -
>
> // JScript Source Code
> class EvalClass
> {
> function Evaluate(expres sion)
> {
> return eval(expression );
> }
> }
>
> 2. Compile it to a dll (evaluator.dll) :
>
> jsc /target:library evaluator.js
>
> 3. Reference the dll in your VB.NET project.
>
> 4. Write Code:
>
> Dim ec As New EvalClass()
> Dim expr As String = "(10 + 6) / 8"
> Dim res As Double = CType(ec.Evalua te(expr), Double)
>
> Console.WriteLi ne("{0} = {1}", expr, res)
>
> You can also pass in bits of JScript code, and have them executed :)[/color]

Regards - OHM# OneHandedMan@BT Internet.com

Is it possible to execute a string in VB.Net (like Eval in VBScript)

Is it possible to execute a string in VB.Net (like Eval in VBScript)

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