XL98: IsDate Function Incorrectly Identifies Some Expressions (184522)


The information in this article applies to:

  • Microsoft Excel 98 Macintosh Edition
This article was previously published under Q184522

SYMPTOMS

In Microsoft Excel 98 Macintosh Edition, if you run a Visual Basic for Applications macro that uses the IsDate function to determine whether an expression can be converted into a date, the function may return the Boolean value True. This result is incorrect.

CAUSE

This problem occurs if the expression that is being evaluated by the IsDate function uses a date format that is not normally recognized as valid by Microsoft Excel. The following date formats are not recognized. 
   Format           Example
   -----------------------------
   year-day-month   2002, 5 July
   month-year-day   July, 2002 5
   day-year-month   5, 2002 July
Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. For example, if you run the following macro 
   Sub TestIsDateFunction()
 
       MyDate = "2002, 5 July"   'an invalid date expression
       MsgBox IsDate(MyDate)     'is it a date?
 
   End Sub
the message box displays True instead of False even though the date is not valid in Microsoft Excel.

RESOLUTION

If an expression uses a date format that includes a year, a month, and a day, in any order, the IsDate function returns True. There is no way to prevent this behavior.

However, you can use the CDate function to convert invalid expressions into valid dates, for example: 
   Sub ConvertDate()
 
       MyDate = "2002, 5 July"   'an invalid date expression
       CnDate = CDate(MyDate)    'convert MyDate into a valid date
       MsgBox CnDate             'display the new, valid date
 
   End Sub

STATUS

This behavior is by design of Visual Basic for Applications.

MORE INFORMATION

Depending on the regional settings that are in use on your computer, Microsoft Excel normally recognizes expressions that use any of the following formats as dates. 
   Format           Example
   -----------------------------
   month-day-year   July 5, 2002
   day-month-year   5 July, 2002
   year-month-day   2002, July 5
For example, if you enter "July 5, 2002" into a cell, Microsoft Excel converts this expression into a proper date.

Expressions that use other formats (such as year-day-month) are not recognized as dates by Microsoft Excel. However, because of the design of the IsDate function, it returns True for any expression that contains a year, a month, and a day, in any order.
Modification Type:MajorLast Reviewed:6/17/2005
Keywords:kbcode kbdtacode kbprb kbProgramming KB184522
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