Article ID: 87970 - Last Review: December 12, 2003 - Revision: 2.0

How to Emulate MKI$ and CVI in VB Using Windows HMemCpy

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SUMMARY

Visual Basic for Windows does not support the MKx$ and CVx family of conversion functions found in earlier versions of Microsoft QuickBasic and Basic Professional Development System (PDS) for MS-DOS. However, you can write functions that provide this support using the hmemcpy API routine provided by Windows version 3.1.

This article provides example routines that simulate the MKI$, MKL$, MKS$, MKD$, CVI, CVL, CVS, and CVD functions.
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MORE INFORMATION

The MKx$ functions convert numeric values to strings by placing the ASCII value of each byte that represents the numeric value into a string. 
Function   Description
---------  ---------------------------------------------------------
MKI$       Converts an integer to a 2-byte string
MKL$       Converts a long-integer to a 4-byte string
MKS$       Converts a single precision variable to a 4-byte string
MKD$       Converts a double-precision variable to an 8-byte string
The CVx functions convert strings created with the MKx$ functions back into numeric values. 
Function   Description</H3>
---------  ---------------------------------------------------------
CVI        Converts a 2-byte string created with MKI$ to an integer
CVL        Converts a 4-byte string created with MKL$ to a long integer
CVS        Converts a 4-byte string created with MKS$ to a single-
           precision number
CVD        Converts an 8-byte string created with MKD$ to a double-
           precision number
The hmemcpy API function can be used to emulate these functions as demonstrated in the example below. Note that the hmemcpy API function is not provided with Windows version 3.0, so the example below requires Windows version 3.1.

The hmemcpy routine copies bytes from a source buffer to a destination buffer. You can use this routine to copy the value of each byte in a numeric value to a corresponding byte in a string to emulate the MKx$ functions. Similarly, you can use the same technique to copy the bytes from a string to a numeric value, to emulate the CVx functions.

NOTE: The hmemcpy routine requires the addresses pointing to the actual location of the data to be copied from and written to. Therefore, it is necessary to pass strings by value (ByVal) in order to pass the location of the string data, as opposed to passing the location of the string descriptor. Similarly, it is necessary to initialize the string size by assigning the string to an appropriate number of characters.

To use the following routines in your Visual Basic for Windows application, you must Declare the hmemcpy routine. Add the following code to the general declarations section of the form: 
   ' Enter the following Declare statement on one, single line.
   Declare Sub hmemcpy Lib "kernel" (hpvDest As Any, hpvSource As Any,
      ByVal cbCopy As Long)

   Function MKI$ (x As Integer)
      temp$ = Space$(2)
      hmemcpy ByVal temp$, x%, 2
      MKI$ = temp$
   End Function

   Function CVI (x As String) As Integer
      If Len(x) <> 2 Then
         MsgBox "Illegal Function Call"
         Stop
      End If
      hmemcpy temp%, ByVal x, 2
      CVI = temp%
   End Function

   Function MKL$ (x As Long)
      temp$ = Space$(4)
      hmemcpy ByVal temp$, x&, 4
      MKL$ = temp$
   End Function

   Function CVL (x As String) As Long
      If Len(x) <> 4 Then
         MsgBox "Illegal Function Call"
         Stop
      End If
      hmemcpy temp&, ByVal x, 4
      CVL = temp&
   End Function

   Function MKS$ (x As Single)
      temp$ = Space$(4)
      hmemcpy ByVal temp$, x!, 4
      MKS$ = temp$
   End Function

   Function CVS (x As String) As Single
      If Len(x) <> 4 Then
         MsgBox "Illegal Function Call"
         Stop
      End If
      hmemcpy temp!, ByVal x, 4
      CVS = temp!
   End Function

   Function MKD$ (x As Double)
      temp$ = Space$(8)
      hmemcpy ByVal temp$, x, 8
      MKD$ = temp$
   End Function

   Function CVD (x As String) As Double
      If Len(x) <> 8 Then
         MsgBox "Illegal Function Call"
         Stop
      End If
      hmemcpy temp#, ByVal x, 8
      CVD = temp#
   End Function
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REFERENCES

"Microsoft Windows SDK: Programmer's Reference," Volume 2: Functions," version 3.1
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APPLIES TO
  • Microsoft Visual Basic 2.0 Standard Edition
  • Microsoft Visual Basic 3.0 Professional Edition
  • Microsoft Visual Basic 2.0 Professional Edition
  • Microsoft Visual Basic 3.0 Professional Edition
  • Microsoft Visual Basic 1.0 Standard Edition
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Keywords: 
KB87970
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This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
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