ASP Classic KB: ASP Classic Topic

An example of using ASP's Response.Write and creating functions.

Call Application.Lock to freeze ASP code while you set IIS application variables the Application.Unlock to unfreeze. No actions take place on the server while locked. 

Arrays in ASP Classic use a 0-based indice.

Use UBound to get the number of elements. UBound returns -1 if the array has no elements, 0 if it has 1, 1 if it has 2, etc.

ASP Classic uses = for it's assignment operator.

Use the scriptiing dictionary object which is available on later versions of ASP Classic (all still commonly in use). Both Access VBA and VB Classic use a collection for this but collections are not supported in ASP Classic.

ASP Classic is not case sensitive. My preference for all languages where case sensitivity does not matter is to use camel caps as in the first example above. Many developers coming from a case sensitive language prefer to use all lowercase.

Ultra-primitive (no inheritance) but useful and encourages you to think and design using objects.

In .ASPhtml pages, you embed ASP code between <% and %>.

ASP Classic code blocks are surrounded by statement ending keywords that all use End such as End Sub, End If, and WEnd.

Commenting Code
ASP Classic, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). ASP Classic does NOT have a multiple line comment.

Preprocessor Directives - @ and #
An @ is used for preprocessor directives within ASP code (within <% %>) and a # is used for HTML-style preprocessor directives.

Note: ASP Classic does not support VB Classic's #If directive.

Scope can be Public or Private. Public Const is the same as just specifying Const. As with variables, all constants are variants. You do not specify the type, it's implied.

When an object instance is created from a class, ASP calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, ASP calls a special sub called Class_Terminate.

ASP Classic is a non-OOP language with some OOP features. It offers both Subs and Functions. A Sub does not return a value while a Function does. When Subs and Functions are used in a defined class, they become the methods of the class.

With ASP Classic, you simply copy your files to a web server that is capable of running ASP pages. This includes your .ASP pages along with supporting files such as images, include files, and database files.

Optionally, you can also deploy a global.asa file which is used to code certain events like application start, application end, session start, and session end.

When an object instance is destroyed, ASP calls a special parameter-less sub named Class_Terminate. For example, when the variable falls out of scope. Since you cannot specify parameters for this sub, you also cannot overload it.

When an object instance is created from a class, ASP calls a special sub called Class_Initialize.

Languages Focus: Development Tools

Primary development tool(s) used to develop and debug code.

In ASP, using ADO, you use RecordSet.AddNew to add a new record, Recordset.Update to post the record, and RecordSet.Delete to delete it. To edit a record, you open the RecordSet using an editable cursor.

In ASP Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Languages Focus: End of Statement

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

Run-time error '3709':
Operation is not allowed on an object referencing a closed or invalid connection.

Languages Focus: Exception Trapping

A common usage of exception handling is to obtain and use resources in a "try-it" block, deal with any exceptions in an "exceptions" block, and release the resources in some kind of "final" block which executes whether or not any exceptions are trapped.

.asp is the default extension for Active Server Pages (ASP) although some developers will change the default extension in an effort to add an additional security level. Although there is no clear standard for include files, using .INC is common but you must make sure that .INC files are not executed nor displayed.

In ASP, using ADO, you filter a set of records using Filter.

In ASP, using ADO, you use Find and Seek to move a cursor of a RecordSet to a matching record.

The End If is optional if you put your code on a single line.

General Info: Inheritance

The concept of a class makes it possible to define subclasses that share some or all of the main class characteristics. This is called inheritance. Inheritance also allows you to reuse code more efficiently. In a class tree, inheritance is used to design classes vertically. (You can use Interfaces to design classes horizontally within a class tree.) With inheritance, you are defining an "is-a" relationship (i.e. a chow is-a dog). Analysts using UML call this generalization where you generalize specific classes into general parent classes.

ASP Classic Inheritance

Although ASP Classic does support simple classes, it does not support interfaces.

ASP Classic Left

• Reference: http://msdn.microsoft.com/en-us/library/sk3xcs8k(VS.85).aspx

Literals are quoted as in "Prestwood".  If you need to embed a quote use two quotes in a row.

Same as VB. ASP Classic logical operators:

ASP Classic does support member fields, but, as usual, you cannot initialize the type nor value of a member field. The type is implied by usage.

ASP classic uses the keywords sub and function. A sub does not return a value and a function does. Many programmers like to use the optional call keyword when calling a sub to indicate the call is to a procedure.

Other than visibility modifiers Public and Private, the only other member modifier available in ASP Classic is Default which is used only with the Public keyword in a class block. It indicates that the sub, function, or property is the default method for the class. You can have only one Default per class.

ASP classic uses the property keyword and special Get and Let methods to both get and set the values of properties.

The member visibility modifiers are Private and Public. If not specified, the default is Public. Private and Public have the usual meaning. Private members are visible only within the class block. Public members are visible within the class and outside of the class.

ASP Classic does not support any type of overloading.

• Operator - No.
• Method - No.

Some developers like to pass in an array and then handle the array for a pseudo technique. Although not overloading, it's useful.

Language Overview: Class-based language. Although you can create classes, ASP is not fully OOP. It is a traditional language with a few OOP extensions. You code in a traditional approach using functions, procedures, and global data, and you can make use of simple classes to help organize your reusable code.

Target Platforms: ASP Classic is most suitable for creating websites targeting any browser (IIS Web Server with ASP Classic installed or equivalent).

By Reference or Value
For parameters, you can optionally specify ByVal or ByRef. ByRef is the default if you don't specify.

ASP uses MoveFirst, MoveLast, MoveNext, and MovePrevious to move a database cursor (a RecordSet).

Because ASP Classic targets a client browser (a document interfaced GUI), a common solution is to simply output an HTML formatted page with black text and a white background (not much control but it does work for some situations).

Same as VB. The Me keyword is a built-in variable that refers to the class where the code is executing.

In ASP, using ADO, you sort a set of records using the Sort property.

Although ASP Classic supports the creation of simple classes, it does not support static methods.

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

An operation with only one operand (a single input) such as + and -.

ASP Classic is a loosely typed language. No variable types in ASP (all variables are variants). Declaring variables is even optional unless you use the Option Explicit statement to force explicit declaration of all variables with Dim in that script. Using Option Explicit is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope.

For example, at the top of my common include file, I have the following:

The following function demonstrates one technique for coding a Yes/No dropdown. It uses a for loop which can be expanded to handle more than the 3 states (Y, N, and blank).

Example of calling the function:

To redirect from http to https, check the Request.ServerVariables HTTPS field and then use Response.Redirect if set to "off".

What is the syntax in ASP Classic for using an associative array?

Use Application.Contents.RemoveAll and Session.Contents.RemoveAll

How do you find last Monday? I want to return a date for last Monday or today if today is Monday.

This function uses Split to count the number of strings within a string.

Short-circuit evaluation is a feature of most languages where once an evaluation evaluates to False, the compiler evaluates the whole expression to False, exits and moves on to the next code execution line. The ASP Classic if statement does not support short-circuit evaluation but you can mimic it. Use either an if..else if..else if statement or nested if statements. ASP code that makes use of this technique is frequenlty clearer and easier to maintain than the short-circuit equivalent.

Response.Flush sends the contents of the buffer to the browser. This command is useful for showing a visitor something while slow loading pages load.

A quick comparison.

How to use ASPMail to send email from your web site.