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ASP ADVANCED
This section describes
how to read and write to a text file.
There are many uses for a text file, including these common ones:
Writing to a Text File To create and write to a text file, you can use the FileSystemObj ect and TextStream objects. First, you must create an instance of the FileSystemObject object. Next, you call the CreateTextFile( ) method of the FileSystemObject object to return an instance of a TextStream object. Finally, you use the Writeline( ) method of the TextStream object to write data to the file. Here's an example: <% This
example creates a file named test. txt with the path c: \mydir\ test. txt.
The WriteLine( ) method is used to send the single line of text
Hello There! to the file. Finally,
the instance of the TextStream object is closed to preserve system
resources. Each of these
steps is described in more detail in the following paragraphs. The CreateTextFile( ) method is used to create the new text file. When this method is called, a TextStream object is returned. This method has one required parameter and two optional ones:
After
a file has been created with the CreateTextFile( ) method, you can use the
TextStream object to write to the file.
When using the TextStream object
for writing, you can use the following methods:
For
example, to create a text file containing the text Hello world! 32
times in a row, you would use the following script: <% Reading and Appending Data from a Text File To
read from a text file, you first need to create an instance of the
FileSystemObject object. Next,
you use the OpenTextFile( ) method to return an instance of the TextStream
object. Finally, you can use
the ReadLine method of the Textstream object to read from the file.
Here's an example: <% This
script reads everything from the text file named test.txt.
It outputs the contents of this file to the browser.
If the file doesn't exist, the error File Not Found
is returned. (In the next section, you learn how to detect whether a file
exists.) The
WHILE...WEND loop in this example
moves through the contents of the file until the end of the file is
reached. The AtEndOfStream
property has the value FALSE until the loop moves to the end of the file. The
following properties of the TextStream object are useful when reading from
a text file:
Instead of using the ReadLine method to read through the contents of a file, you can use the Read( ) method. The Read( ) method returns a specified number of characters from an open text file. Following is an example of how to use this method: <% This script retrieves the first line from a text file, one character at a time. The AtEndOfLine property detects when the end of the first line of the text file has been reached. The Read( ) method reads one character at a time from the text file. The following methods are useful when reading data from a text file (continued on the next page):
Normally,
the OpenTextFile( ) method is used for retrieving data from a text file.
However, you can also use this method to append new
data to a text file, like this: <% This script creates a log of the browsers being used at a Web site. Whenever the script is executed, the type of browser used to request the page is recorded in a text file. This browser information is retrieved from the ServerVariables collection. The
preceding script appends the browser type to the end of the text file
named browser.log. If the
file browser.log doesn't exist when this script is first executed, the
file is created automatically. This
is accomplished by using two parameters of the OpenTextFile( ) method: the
IOMode and the Create parameters. The
following list describes all the parameters of the OpenTextFile( ) method:
Sample
Application This
section provides a sample application of the methods used for reading and
writing to files. As I write
this, Amazon.com (the online bookstore) is holding a competition to write
a collaborative online story. The
first part of the story was entered by John Updike.
Each day, visitors to the Amazon.com Web site submit new sentences
to add to the story. One
sentence is selected every day, and the winner receives $ 1,000.
The story is being written collaboratively. This
competition is a great idea. It
attracts repeat visitors to the Amazon.com Web site, and it has generated
a tremendous amount of publicity. You
may want to add something similar to your Web site.
Listing below shows a simple example of how you could do this. <% This
Active Server Page contains two scripts.
The first script executes when a new sentence has been submitted.
If a new sentence exists, it's appended to the file named
TheStory.txt. The
second script is used to display the contents of the TheStory.txt file.
Each line in the file is outputted.
The lines are separated by two nonbreaking space characters so that
the sentences will be divided by spaces when displayed. The remainder of the Active Server Page contains an HTML form for submitting the next line in the story. The Active Server Page posts the form contents to itself. For this to work, you must name the Active Server Page story.asp. Before
you use this Active Server Page for the first time, you need to create a
text file named TheStory.txt. The
first sentence of the story needs to be entered into this file.
If you want to restart the story, simply c!ear this file and enter
a new first sentence.
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