extra stuff
Description |
Tip |
| A caveat when using ASP's Response.Redirect method | When ASP encounters the Response or End methods, it immediately halts script execution in both the GLOBAL.ASA file and in the application page. As a result, ASP won't execute any script that follows the Redirect method. Instead, it either ends the session or begins processing the new page. For this reason, you should always make the Redirect method the last call in any script. |
| Avoid boolean comparison errors in ASP | Often in VBScript, you'll want to determine if a numeric value is
greater than zero then perform some action based on the results. For
example, you'll often want to know if a recordset contains records. To do
so, you can simply use the results in a boolean expression, like so If rst.RecordCount Then 'Do something End If This works because VBScript, like VB and VBA, considers any non-zero number (negative or positive) a True boolean value. Be warned, however, that bugs can occur when you try to use Not with this same expression, as in If Not rst.RecordCount Then You might think this test would determine if the recordset didn't contain records. It does when the RecordCount property returns -1 ((Not -1) = 0). However, if the property returns the actual number of records, then this condition statement returns True. That's because when you use Not on a number, VBScript returns the opposite value of that number minus one. For instance, the expression Not 15 returns -16, which as you know VBScript interprets as True. With regard to the record count test, if the property returns -1, then there's no problem, since the result is (1-1) or 0. However, when the property contains an actual value, then Not rst.RecordCount evaluates to a non-zero number, which again VBScript evaluates as True. To get around this minor glitch, you can use one of the following statments: If Not Cbool(rst.RecordCount) Then or If Not (rst.RecordCount<>0) Then or simply If rst.RecordCount = 0 Then |
| Create Visual InterDev 6.0 ASP code templates | Instead of retyping the same code lines on virtually every ASP page that
you create in Visual InterDev 6.0, simply open Program Files | Microsoft
Visual Studio | VIntDev98 | Templates | Web Project Items | New ASP
Page.asp file, and then enter the code that you want duplicated, i.e.
included files, titles, metatags. Save your work, and any new ASP page
that you create will contain the new code. Submitted by: Will Smith [will@newtweb.com ] |
| Determine browser capabilities in an ASP page | When you use the Browser Capabilities component in an ASP page, you can
determine client browser attributes: such as if the calling browser
supports frames, VBScript, or javascript. You can also determine the
browser's version and type, such as Internet Explorer 5.0, or Netscape
Navigator 4.6. For example, to determine if a browser supports frames, you
could use code similar to: <% Dim objBrowsCap Dim blnAllowsFrames Set objBrowsCap = Server.CreateObject ("MSWC.BrowserType") blnAllowFrames = objBrowsCap.frames If blnAllowFrames Then 'Code for frames goes here Else 'Code for non-frames goes here End If Set objBrowsCap = Nothing %> Unfortunately, this component relies upon the server's browscap.ini file to determine the latest information on client browser. The Browser Capabilities component simply reads the INI file and returns the values contained therein. If the browscap.ini file is out of date and doesn't have information on the requesting browser, the component uses the INI file's default values, which may or may not contain the correct capablilities. To avoid having to constantly update the INI file yourself, you can check out Cyscape, Inc.'s Web site at http://www.cyscape.com/browscap . They offer a continually updated INI file. In addition, they've developed a utility called BrowserHawk that, among other features, automatically detects new browsers and updates the appropriate files. |
| Eliminate default page renaming | Have you ever experience the annoying problem where Copy Web copies the Web to the appropriate server but renames the default.asp page to default.htm? The problem is really caused by a bug in the Microsoft FrontPage extensions. Any Web application that contains a Default.asp in the root will rename the file when copied using the "Copy Web Application" command to default.htm in the destination Web application. To eliminate the problem, simply add a page named default.htm to the existing Web site. |
| Ensure accurate string comparisons in ASP pages | As you probably know, the StrComp() function provides a quick way to
compare two strings. It takes the following syntax: StrComp( string1, string2, comparemode) VBScript compares the two strings according to either the comparemode argument, or the default setting on the server. This function returns 1 if the first string is greater than the second string, 0 if the two are equal, and -1 if the first string is less than the second. However, if you want to compare strings taken from user input, to ensure that the results are accurate, remove any extra spaces from the two strings. For example, you could use something like: StrComp( Trim(str1), Trim(str2)) Strings with extra spaces will provide inaccurate results. To illustrate, create the following ASP page, and then view it in Internet Explorer. <html> <head> <script language="VBScript"> sub mySort() Dim str1, str2, ary, sCompare str1 = document.all.txt1.value str2 = document.all.txt2.value Select Case StrComp(trim(str1), trim(str2)) Case 1: sCompare = "greater than" Case 0: sCompare = "equal to" Case -1: sCompare = "less than" End Select MsgBox str1 & " is " & sCompare & " " & str2 end sub </script> <body> <form> <input type="text" id="txt1" /><br /><br /> <input type="text" id="txt2" /><br /><br /> <input type="button" value="Compare" onclick="mySort" /> </form> </body> </html> First, enter an A; into the first field and a Z; into the second, then click the Compare button. When you do, VBScript informs you that A is less than Z, as you would expect. Now, enter a space before the Z and click the button again. This time the message box inaccurately claims that A is greater than Z. |
| Ensure proper remote scripting parameter types in ASP | As you probably know, remote scripting is a great way to access
server-side functions and procedures from client-side scripting. However,
when you use parameters in a server-side function intended for client-side
use, remember that IIS converts all parameter values into strings. As a
result, if necessary, you'll want to convert these values back into their proper data type within the server-side function. Also, keep in mind that for security reasons, IIS doesn't let you pass structured data (objects or arrays) as remote scripting parameters. |
| Generate accurate ADO RecordCount values in ASP | As you know, the ADO RecordCount property returns the number of records
in an ADO recordset. Of course, in several instances, this property also
returns a -1 instead. The value RecordCount returns depends on the
recordset's cursor type: -1 for a forward- only cursor; the actual count
for a static or keyset cursor; and either -1 or the actual count for a
dynamic cursor, depending on the data source. You may be surprised to learn that RecordCount will be -1 for recordsets created with the Execute method from a Connection or Command object. That's because this method generates a forward-only recordset, which, as we mentioned earlier, returns -1. As an example, enter and run the following procedure in a standard ASP page. When you open it, the page displays -1 for the recordset based on myConRst, and 6246 for myKeyRst. <% Dim myConn, myComm, myConRst, myKeyRst Dim sConnection sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" & _ "Data Source=D:\Microsoft Visual Studio\VB98\Biblio.mdb" Set myConn = Server.CreateObject("ADODB.Connection") Set myKeyRst = Server.CreateObject("ADODB.Recordset") myConn.Open sConnection myComm = "Select * From Authors" Set myConRst = myConn.Execute(myComm, , 1) myKeyRst.Open myComm, myConn, 1 %> RecCount <BR/> From Connection: <%=myConRst.RecordCount %><BR/> From Recordset: <%=myKeyRst.RecordCount%> <% Set myKeyRst = Nothing Set myConRst = Nothing Set myConn = Nothing %> |
| Globally replace text using just 5 lines of VBScript | If you've ever tried to implement a text search and replace function in an ASP page, you probably resorted to lengthy parsing loops that used Instr() and an entire host of string functions. If so, you'll be glad to know that there's a much easier way. With the advent of VBScript 5.0, (IIS 5.0) Microsoft introduced the Regular Expression engine. If you've used Perl or javascript, you may be familiar with these pattern-matching powerhouses. In a nutshell, regular expressions let you define a pattern, literal or representative, which you can then match against a second string. For example, the literal pattern 'abc' as a regular expression would find a match in 'dabcef', 'abcdef', or 'defabc'. To further refine a regular expression, the Regular Expression engine offers a host of special metacharacters, similar to wildcard characters. For example, using these metacharacters, you could search for any word that began with a letter and ended in a digit. To view these metacharacters and their uses, visit http://msdn.microsoft.com/scripting/default.htm then search in the VBScript documentation for the RegExp object's Pattern property. (If you don't have IIS 5.0, all you really need is the latest version of VBScript, which you can download from http://www.microsoft.com/msdownload/vbscript/scripting.asp ) To create a simple find and replace subroutine with client-side VBScript, first create a RegExp object, like so <script language="VBScript"> Sub GoReplace() Set myReg = new RegExp Next, set the object's properties. myReg.IgnoreCase = True myReg.Global = True myReg.Pattern = "abc" Here, we've used a literal string to create a global, case- insensitive pattern. Finally, you execute the object's Replace method on a target string, as in document.all.myTextArea.value = myReg.Replace(document.all.myTextArea, "def") End Sub </script> That's *all* there is to it! This example would replace "abc" with "def" wherever it occurred within myTextArea. To execute the replace on the first matching string only, set the Global property to False. |
| How to Increase the Speed of Large Uploads | If you anticipate large uploads, increase Internet Information Server's
(IIS) UploadReadAhead value to enable faster transfers. UploadReadAhead is
an IIS parameter that contains the amount of data that the server will
read before passing control to the application. The application is then
responsible for reading the rest of the data. The default UploadReadAhead
is 48kb. With a higher UploadReadAhead, transfers will be faster, but
uploading will utilize more physical memory. If you increase the
UploadReadAhead value, increase the amount of RAM on the server as well. To increase the UploadReadAhead value, 1. Go to Start\Run 2. Enter regedt32 to open the registry 3. Open, HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ W3SVC\ Parameters\ UploadReadAhead 4. Highlight the UploadReadAhead value (in the right frame) 5. Open Edit and select DWORD 6. Enter a new value in the Data window If the UploadReadAhead parameter does not exist in your registry, you can add it. To add the parameter, 1. Open the Edit menu 2. Select Add Value 3. Enter "UploadReadAhead" in Value Name 4. Enter REG_DWORD in Data Type 5. Click Ok Enter the value in kb |
| Include VBScript variables in ASP SQL statements | Often, you'll no doubt want to include a VBScript variable in an ASP SQL
statement. For example, suppose you want to let a user search a table for
names that begin with a letter they specify. To use a variable in a SQL
statement, simply concatenate the various parts of the statement together.
To see how this works, create an ASP page with the following code: <HTML> <BODY> <FORM Name="test" Action="SQLVars.asp" Method="POST" > <INPUT Name="txtSearch" TYPE="TEXT" Size=15 VALUE="SearchForMe"> <INPUT Type="SUBMIT" VALUE="Submit"> </FORM> <% Dim strSQL1 Dim strSQL2 Dim strSearch strSearch = Request.Form("txtSearch") If Len(strSearch) Then strSQL1 = "Select From Customer(MyField) Where " _ & "Name(Col.Name) Like 'strSearch%'" strSQL2 = "Select From Customer(MyField) Where " _ & "Name(Col.Name) Like '" & strSearch & "%'" End If %> <UL> <LI>Before concatenation: <%=strSQL1%> <LI>After concatenation: <%=strSQL2%> </UL> </BODY> </HTML> When you run the page, only strSQL2 contains the variable's actual value, which can then be sent on to SQL Server, or any other database that processes SQL statements. Also, notice the use of the single quote before the double quote and after the percent sign. This ensures that the database interprets the variable's value as a string. |
| Let the Scripting type library verify a file's existence | The FileSystemObject offers a great way to manipulate a server's
directory structure. With the FileExists method, you can determine if a
file exists at runtime. This method conforms to the following syntax: object.FileExists(filespec) where object is a FileSystemObject variable and filespec is the file's path (absolute or relative). If you expect the file to be in the same folder as the ASP page running the script, then you only need to specify the filename. This method follows the same syntax in both VBScript and javascript. So, suppose you wanted to use this handy method to search for a file in an images folder. To do so, use code similar to blnExists = fso.FileExists(Server.MapPath("/images/Some.gif") Here, the code searches the server's root directory for the Some.gif file. It returns True if the file exists, and False if not. In addition to the FileExists method, the FileSystemObject also exposes FolderExists and DriveExists methods, both of which follow the same syntax. |
| Obtain a header list with ASP's ServerVariables collection | The SeverVariables collection contains all kinds of information about
the calling client and the server. For instance, you can determine a
visitor's browser type with the HTTP_USER_AGENT variable. Or, you can use
HTTP_REFERER to determine the referring Internet address. Not all browsers
support the same headers, however. To see a quick list of the headers
supported within a browser, run the following code. <HTML> <BODY> <TABLE BORDER=1> <TH COLSPAN=2>ServerVariables</TH> <% For Each var in Request.ServerVariables With Response .Write("<TR>") .Write("<TD><B>" & var & "</B>:</TD>") .Write("<TD>" & Request.ServerVariables(var) _ & "</TD>") .Write("</TR>") End With Next %> </TABLE> </BODY> </HTML> |
| Parsing multiple selected options in server-side ASP | In a previous tip, we showed you how to gather multiple selections from
an HTML Select element on the client side. However, when you obtain these
values after a Get or Post request, you need to use a different technique.
That's because these multiple values get passed as a comma-delimited
string. So, say you had a Select element named "Lst1" on a form.
If you selected three options with values 5, 6, and 7, and submitted the
form, then Request.Form("Lst1") would contain the string "5, 6, 7". As a result, you'll need to parse this string to get the individual values. To do so, you have two options. First, you can use the Split() function to place the values into an array. Or, if you don't have a version of IIS that supports the Split() function, you can use the Instr() function and search for the comma character within the string. As an example, create an HTML page named GetOptions.html and add the following form to it: <form id="frm1" action="GetOptions.asp" method="post"> <select size=10 multiple="multiple" name="Lst1" id="Lst1"> <option value="1">Sunday</option> <option value="2">Monday</option> <option value="3">Tuesday</option> <option value="4">Wednesday</option> <option value="5">Thursday</option> <option value="6">Friday</option> <option value="7">Saturday</option> </select> <br /><br /><input type="submit"> </form> Next, create an ASP page named GetOptions.asp and add the following code: <% ' Parse request string using Split() Dim sSelected, arySelected, x sSelected = Request.Form("Lst1") Response.Write("You selected: " & sSelected & "<br />") Response.Write("<br /><b>Split()</b><br />") arySelected = Split(sSelected, ",") For x = 0 to Ubound(arySelected) Response.Write("Choice " & x & ": " & arySelected(x) & "<br />") Next Response.Write("<br /><b>Instr()</b><br />") ' Parse request string using Instr() Dim subString x = 0 sSelected = sSelected & "," Do Until Instr(sSelected,",") = 0 Response.Write("Choice " & x & ": " & Left(sSelected, _ instr(sSelected,",") -1) & "<br />") sSelected = Mid(sSelected, instr(sSelected,",") + 1) x=x+1 Loop %> Note, that the same techniques would work with Response.QueryString("Lst1") as well. |
| Prevent spam before it starts with our Jscript | If you're like us, then you're getting really, *really* tired of all the spam mail piling up in your in box. While we can't tell you how to get rid of it entirely, we can give you a tip that will help cut down on spam. As you may know, most spam list generators work by browsing the Web and gleaning email addresses from Web sites. Because of an email address' distinct format, it's pretty easy to find one in a page. Well, you'll be happy to know there's a technique that lets your email addresses show up in a page, but still defeats the spam list spiders. The trick is to use a javascript function, like the one that follows, to generate the email addresses: <script language="javascript"> <!-- Hide from old browsers function ShowAddress(part1, part2) { var addr = part1 + "@" + part2; var result = ("<a href='" + "mail" + "to:" + addr + "'>" + addr + "</a>") return result; } //--> </script> To make an email address appear in the page, call the function like so: <script language="javascript"> <!-- document.write(ShowAddress("wdv","zdjournals.com")); //--> </script> Now, won't those spam list spiders be baffled! Submitted by: Vik Nokhoudian, World Wide Web Associates [vik@wwwa.com ] |
| Register WSC scripts before using them in ASP | The Windows Scripting Component is a great tool that let's you create
COM components for use in ASP pages. What's more, you can use either
VBScript or javascript to give them functionality. When you create a WSC
component, however, you must register it before you can use it in an ASP
page. To do so, open Windows Explorer and right-click on the WSC file you
just created. Select Register from the shortcut menu. To create an object
variable based on the new script object, use code similar to Set objXMLCreate = Server.CreateObject("MyScriptObj.WSC") At this point, you're free to access any of the object's methods and properties. |
| Setting checkbox values from an Access database | Often you'll want to display a checkbox value stored in an Access
database in an ASP page. Depending on the setting in your Access table,
Access may display Yes/No, On/Off, or True/False in the field when you
view the table in the database. As a result, you may think to use ASP
similar to <input type="checkbox" name="chk1" value="Yes" <% if rs("checkfield")="yes" then %> checked="checked" <% end if %> /> However, this doesn't actually work. That's because even though Access displays the field contents as a Yes or No, it stores the contents as True or False, (-1 and 0 respectively). To get an accurate checkbox setting in ASP, use <input type="checkbox" name="chk1" value="Yes" <% if rs("checkfield")=True then %> checked="checked" <% end if %> /> |
| Simplify loading stored |
When loading an <OPTIONS> list from a database table, it's much
easier to call a procedure that uses process parameters. This way, you can
use the same procedure for several different operations. For example,
suppose you want to fill a Listbox with a list of animals. In addition,
you've set up several checkboxes on a Web page that let the user simply
view the list, or load the list with one of the animals already selected.
The following example shows how you might process the resulting page. (To
save space, we hard-coded the two parameters.) <!-- #include File="DBConnect.Asp" --> <HTML> <BODY> <FORM> <SELECT name=Atype size= 5> <% Dim chkMode chkMode = 2 'or Request.Form("chkMode") fillOptionList chkMode,"Snake" %> </SELECT> <% Sub fillOptionList(myMode, optionValue) Dim rsAnimal Dim strSelected set rsAnimal = CreateObject("ADODB.recordset") With rsAnimal .Open "tblAnimals", strDB, adOpenStatic,,adCmdTable Do While Not .EOF Select Case myMode Case 1 strSelected = "" Case Else If optionValue = rsAnimal("Animal") Then strSelected = " SELECTED" Else strSelected = "" End if End Select Response.Write("<OPTION" & strSelected & " VALUE=" _ & rsAnimal("ID") & ">" & rsAnimal("Animal") & "</OPTION>") .MoveNext Loop .Close End With Set rsAnimal = Nothing End Sub %> </BODY> </HTML> For the OPTION elements, this code produces output HTML like this: <SELECT name=Atype size= 5> <OPTION Value=1>Cat</OPTION> <OPTION Value=2>Cow</OPTION> <OPTION Value=3>Dog</OPTION> <OPTION SELECTED Value=4>Snake</OPTION> <OPTION Value=5>Elephant</OPTION> <OPTION Value=6>Fish</OPTION> </SELECT> Submitted by: Faisal Ladak [fladak@systech-inc.net] |
| Use a single ADO connection to reduce ASP server load | If you need to execute multiple SQL statements on a single database in a
single ASP page, it's often wise to open a single Connection and reuse it
multiple times. Doing so reduces the number of times the server must open
and close the same database, which can significantly increase the server's
load. To use a single connection, create the database Connection at the
beginning of the page, then destroy it at the end. When you Execute a SQL
statement, whether it returns a Recordset or not, specify the active
Connection. Here's an example. <% strDSN = "DSN=database;UID=username;PWD=password" Set conn = Server.CreateObject("ADODB.Connection") conn.Open strDSN strSQL = "select column from table" Set rsResults=conn.Execute(strSQL, , 1) if not rsResults.eof then temp = rsResults("column") else temp = "No Results" end if 'close the Recordset, but leave the Connection open rsResults.Close strSQL = "delete from table where column=123" conn.Execute strSQL, , 1 'Done executing SQL statements at this point, so close the Connection. conn.Close set rsResults = Nothing set conn = Nothing %> Submitted by: Brian Coverstone [brian@pcioh.com] |
| Use ADO's native OLEDB drivers instead of ODBC | When you create an connection string, ADO gives you a choice between
indicating a data source driver as either a Driver, as in Driver={SQL Server};DBQ=database_file or a Provider, such as Provider=Microsoft.Jet.OLEDB.4.0;Data Source=database_name However, when you use the first option, ADO uses older ODBC drivers to connect to the data source; whereas the second form uses OLEDB, which is ADO's native data access interface. For this reason, you should use the Provider option whenever possible. Such native OLEDB drivers exist for SQL Server, Index Server, Site Server Search, and Oracle, among others. |
| Use VBScript's RegExp object to validate email address syntax | Nowadays, if your Web application requires a user to enter specific company information, you probably have a field for an email address. No doubt, you'll want to ensure that the address not only contains the @ and dot, but that the remaining characters contain only letters, numerals, or underscores (and perhaps a dash or period). At first, this may seem like a daunting task. And if you use standard VBScript's string functions alone, it will be. Fortunately, the RegExp object provides an easier way. The following code validates an email address in a textbox named Text1: <head> <script language="VBScript"> Sub checkEmail(sEmail) Dim myReg Set myReg = New RegExp myReg.IgnoreCase = True myReg.Pattern = "^[\w-\.]+@\w+\.\w+$" msgbox myReg.Test(sEmail) End Sub </script> </head> <body> <form> <input type="text" id="txtEmail" name="txtEmail"></input> <input type="button" onclick="checkEmail(document.forms(0).txtEmail.value)" value="Verify"></input> </form> </body> Here, the pattern accepts any number of numeric, underscore, letters, periods, or dash characters before the @ character and only numerals, underscores, or letters before and after the dot. |
| Why relative filespecs may not work in ASP | Even though the helpfile states you can use relative directory paths
with FileSystemObject objects, you probably encountered an error if you
tried to use them in an ASP path. That's because the directory that
contains the ASP page doesn't become the current directory, as far as the
FileSystemObject is concerned. To illustrate, run the following VBScript
code in an ASP page: <% Set FileObject = Server.CreateObject("Scripting.FileSystemObject") filespec="\test.jpg" CurrDir = FileObject.GetAbsolutePathName(".") Response.Write "Using CurrDir: " & CurrDir & filespec & "<br>" if FileObject.FileExists(filespec) then Response.Write "[CurrDir] File Found<br>" else Response.Write "[CurrDir] No File found<br>" end if Response.Write "Using MapPath: " & Server.MapPath(filespec) & "<BR>" if FileObject.FileExists(Server.MapPath(filespec)) then Response.Write "[MapPath] File Found<br>" else Response.Write "[MapPath] No File found<br>" end if Set FileObject = Nothing %> |