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  2. XL2000: IsDate Function Incorrectly Identifies Some Expressions

XL2000: IsDate Function Incorrectly Identifies Some Expressions

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This article was previously published under Q213665

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Symptoms

If you run a Microsoft 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.

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Cause

This behavior can occur 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
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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.

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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

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More information

Depending on the regional settings that are in use on your computer, 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 type July 5, 2002 into a cell, Excel converts this expression into a proper date.

Expressions that use other formats (such as year-day-month) are not recognized as dates by 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.

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Keywords: KB213665, kbprogramming, kbprb, kbdtacode

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Article Info
Article ID : 213665
Revision : 6
Created on : 11/23/2006
Published on : 11/23/2006
Exists online : False
Views : 284