Access Tip: NULL vs. Zero Length Strings

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2/26/2009 4:18:11 PM
Access Tip: NULL vs. Zero Length Strings
By Richard Rost

I get asked this all the time: "what's the difference between a NULL value and a Zero Length String."

Here's the answer:

/tips/access/null-zls

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Keywords: access tips null zero length string

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Access Tip NULL vs Zero Length Strings Comment from Jeff Martin @ 10/31/2012

In my VBA programming I like to use:

Name=vbNullString

rather than:

Name = ""

Dim Name as string

Name = Empty
Name = vbNullString
Name =

All return true.

According to VB6 testing for an empty string is faster when done this way.

LenB(Text$) = 0

Rather then

Text$ =

LenB the byte equivalent of Len is faster than Len and the test for an inequality is faster than a greater then or less than sign.  LenB never returns a neg number.

Testing for Text$ = "" takes 6 bytes of RAM each time you use it.  A VBA string is only a pointer to a character array.  The address in memory pointed to by this variable points to the start of a character array.  The array is preceded by 4 bytes showing the length of the string in bytes, and terminates with a 2-byte null terminator.   So using a "' to declare an empty string results in a array size of 0 and will contain the 4 byte  length data, and the 2 byte terminator

VbNullString still returns a pointer but one that does not point to any character array resulting in no 4 byte length field or 2 byte terminator.

VbNullString is a string having a value of 0 and is not the same as a ZLS

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