Can I write CGI scripts in Visual Basic?

Contributors:

• MichaelGiordano cissmjg@hotmail.com

---

The answer is YES! You must use either VB4/32, VB5 or VB6. The secret lies in using 3 Win32 API calls :

- GetStdHandle

- ReadFile

- WriteFile

For convenience you might want to declare the following constants :

Private Const STD_INPUT_HANDLE = -10&
Private Const STD_OUTPUT_HANDLE = -11&

Sending output data to the web server is pretty easy so we'll cover that first. Assuming lResult is a long and that the variable sOutput is a String containing information to be displayed, simply call WriteFile as follows :

WriteFile GetStdHandle(STD_OUTPUT_HANDLE), _
          sOutput, _
          Len(sOutput), _
          lResult, _
          ByVal 0&

Getting data from the web server is only slightly trickier. There are two cases METHOD=GET and METHOD=POST. We'll cover METHOD=GET first.

By using the Environ$ function and looping through the environment, the QUERY_STRING environment variable will contain the web server data.

Dim iEnvItem as Integer, iOffset as Integer
Dim sWork as String, sEnvVar as String
Dim sQS as String

iEnvItem = 0
Do
   sWork = Environ$(iEnvItem + 1)
   iOffset = InStr(sWork, "=")
   sEnvVar = UCase(Left(sWork, iOffset - 1))

   If sEnvVar = "QUERY_STRING" Then
      sQS = Mid(sWork, iOffset + 1)
      Exit Do
   End If

   iEnvItem = iEnvItem + 1
Loop

Getting data via METHOD=POST requires a call to ReadFile. Below is a sample code snippet:

'Note that mvarCONTENT_LENGTH contains the CONTENT_LENGTH environment variable.

Dim lpszBuf as String
Dim lBytesRead as Long

lpszBuf = String$(mvarCONTENT_LENGTH + 1, 0)
lBytesRead = mvarCONTENT_LENGTH
lResult = ReadFile(GetStdHandle(STD_INPUT_HANDLE), _
                   ByVal lpszBuf, _
                   mvarCONTENT_LENGTH, _
                   lBytesRead, _
                   ByVal 0&)

A complete VB project (inspired by Chapter 20 of the book CGI by Example by Robert Niles and Jeffry Dwight ISBN: 0-7897-0877-9) is available here.

The project also contains a sample program (Cgitst.vbp) that when compiled and placed in the appropriate cgi-bin type directory will display all CGI variables for an HTML form.

---

Previous | Next | Table of Contents

---