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ch a p t e r

Manipulating Strings



Understanding how string values are stored and

used in VBA



Using the built-in VBA string-handling functions



Searching for and replacing text



Gathering information about strings



Converting strings



Working with substrings

COPYRI

GHTED

MATERI

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Chapter 1

•

Manipulating Strings

lmost any VBA application will need t o handle string (text) data at one

point or another. VBA itself provides a useful set of string-handling functions, but

the functionality of other functions as a whole is not nearly as full-featured as that

provided by other, more text-centric programming languages. This chapter first

makes a quick pass through the existing functions and then provides many useful

routines to add to your string-handling bag of tricks. Surely, no chapter on this

topic could cover every possible combination of useful functions, but the ones we’ve

provided here should give you a good start in writing your own VBA solutions.

The sample files you’ll find on the CD-ROM that accompanies this book are

listed in Table 1.1:

Because the modules for this chapter take advantage of ADO, you’ll need to make

sure your own project includes a reference to the Microsoft ActiveX Data Object 2.1

Library before you import the StringsBAS module into the project. Use the Tools 

References menu (or Project 

References menu, in Visual Basic) to add the neces-

sary reference. Otherwise, your code will not compile once you’ve added the

Strings module to your project.

TABLE 1.1:

String-Handling Functions

Filename

Description

STRINGS.XLS

Excel file with sample functions

STRINGS.BAS

Text file with sample functions

TESTSTR.BAS

Text file with test procedures

PROPER.MDB

Access 2000 database, containing sample for dhProperLookup

PROPER.TXT

Text version of sample for dhProperLookup

PROPER.XML

XML-based recordset for dhProperLookup

STRINGS.VBP

Visual Basic project with sample code

STRINGS.MDB

Access 2000 database, containing sample functions

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How Does VBA Store Strings?

A VBA string is simply a collection of bytes. To make it easier for VBA to work

with strings, each string also maintains its own information about its length. In

addition, unlike other programming languages, VBA takes care of creating,

destroying, and resizing string buffers. You needn’t worry about how VBA finds

strings in memory, whether they’re contiguous in memory, or how or when VBA

reclaims the memory of the string used once you’re done with it.

VBA provides two types of strings:

fixed-length

and

dynamic

. Fixed-length

strings are those you declare with a fixed size, like this:

Dim strFixed As String * 100

In this case, strFixed will always contain exactly 100 characters, no matter how

many characters you’ve placed into it. When VBA first creates the variable, at run-

time, it fills the variable with 100 spaces. From then on, if you attempt to retrieve

the length of the string, the output will always be 100:

Debug.Print Len(strFixed)

VBA fills the extra positions with spaces. You’ll need to use the Trim function in

order to use the string in any other expression (see the section “Working with Por-

tions of a String” later in this chapter for more information). Fixed-length strings

can be no longer than 65,526 characters.

Online help for VBA states that a fixed-length string can be up to 2

(or

65,536) characters long. Not so—if you attempt to create one with more than 65,526

characters, VBA won’t compile your code.

Dynamic strings, on the other hand, have no fixed size. As you add or remove

characters from these objects, VBA takes care of locating memory in which to

place the text and allocates and deallocates memory as necessary for your text. To

declare a dynamic string, you use a declaration like this:

Dim strDynamic As String

In this case, if you retrieve the length of the string, the result will accurately reflect

the amount of text you’ve placed into the variable. Dynamic strings can contain

up to around two billion characters.

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Chapter 1

•

Manipulating Strings

How do you decide which type of string to use? Dynamic strings require a bit

more processing effort from VBA and are, accordingly, a bit slower to use. On the

other hand, you make up the time by not needing to use the Trim function to remove

excess space every time you use the string. As you’ll see by working through the

examples in this chapter, we use fixed-length strings only when it’s necessary.

When working with a single character at a time, it makes sense to use a fixed-length

string declared to contain a single character. Because you know you’ll always

have only a single character in the string, you’ll never need to trim off excess

space. You get the benefits of a fixed-length string without the extra overhead.

Unicode versus ANSI

The 32-bit Windows “universe” supports two character storage mechanisms:

ANSI and Unicode. The ANSI storage standard uses a single byte for every char-

acter, with only 256 different characters allowed in any ANSI character set. If you

want to display characters from a different set of 256, you must load a separate

code page. This limitation makes it difficult to create internationalized applica-

tions. Windows 95 and Windows 98 use this approach for compatibility with pre-

vious versions of Windows. The Unicode standard allows for 65,536 characters,

each taking up two bytes. The Unicode character set includes just about all the

known written characters and ideograms in a single entity. In this way, an appli-

cation that embraces the Unicode standard can support (once its text has been

translated) just about any written language. Windows NT and Windows 2000

support the Unicode standard.

No matter what operating system you’re using, VBA stores strings internally in

Unicode format. That is, every character takes up two bytes of space. When VBA

needs to communicate with Windows 95 or Windows 98 (when you include Win-

dows API calls in your code, for example), it must first convert strings to ANSI

format. This happens automatically when you use the ANSI version of a Win-

dows API call that involves strings. The only other time you’ll care about how

VBA stores strings is when you want to convert a string into an array of bytes—a

useful technique that we’ll take advantage of a few times in this chapter. In this

case, a string containing five characters becomes an array of bytes containing ten

bytes. For example, a string containing the text

Hello

would contain the following

ten bytes, once converted to a byte array:

72 0 101 0 108 0 108 0 111 0

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Unicode versus ANSI

Each pair of bytes (72 and 0 for the

, for example) represents the Unicode stor-

age for a single character. However, if you were running Microsoft Excel in Korea,

for example, and were entering text in your native language, the second byte

wouldn’t be 0. Instead, it would be a value that combined with the first byte to

represent the character you’d typed.

Using Strings and Byte Arrays

Because it’s often faster and simpler to work with arrays of bytes than to work with indi-

vidual characters in a string (and you’ll find some examples in this chapter that use this

technique), VBA provides a simple way to convert strings into byte arrays and back. Simply

assigning a string to a byte array variable causes VBA to copy the data into the array.

When you’re done working with the array, you can assign it right back into the string vari-

able. For example, the following code fragment copies data from a string into a byte array,

performs processing on the array, and then copies the array back into the string:

Sub StringToByteArray()

Dim strText As String

Dim aByt() As Byte

Dim intI As Integer

strText = "Hello"

' VBA allows you to assign a string into

' a byte array and then back again.

aByt() = strText

For intI = LBound(aByt) To UBound(aByt)

Debug.Print aByt(intI);

Next intI

Debug.Print

strText = aByt()

Debug.Print strText

End Sub

Although you won’t use this technique often, if you need to process each byte of a string,

it’s the best solution.

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Chapter 1

•

Manipulating Strings

In previous versions of Basic, many programmers used string variables to contain

binary data (that is, non-textual data, such as bitmaps, sound files, and so on). In

VBA, this isn’t necessary, nor is it advisable. Instead, use arrays of bytes for non-

textual data. Because VBA performs ANSI-to-Unicode conversions on the fly,

you’re almost guaranteed that your non-text data will be ruined once you place it

into a string variable.

Using Built-In String Functions

VBA provides a large number of string-handling functions. This section intro-

duces many of those functions, broken down by the area of functionality, and dis-

cusses the most useful of the built-in functions. The remainder of the chapter

provides techniques that combine the built-in functions to perform tasks for

which you would otherwise need to write custom code.

Comparing Strings

VBA provides three ways for you to compare the contents of one string with

another: comparison operators (such as =, <, and so on), the Like operator, and the

StrComp function. In addition, you can specify the method of comparison for each

module using the Option Compare statement in the declarations area.

Option Compare

The Option Compare statement, if it’s used at all, must appear in a module before

any procedures, and it tells VBA how you want to make string comparisons

within the module. The choices are as follows:

Option Compare Binary

Comparisons are made based on the internal sort

order of the characters, using their binary representation. In this situation, char-

acters are treated case sensitively (that is,

isn’t the same as

Option Compare Text

Comparisons are made based on the text sort order of

the current locale. Characters are treated, at least in English, case insensitively.

Option Compare Database

Is available only in Microsoft Access. Compar-

isons are made based on the locale ID of the current database.

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Using Built-In String Functions

If you don’t specify an Option Compare setting, VBA uses Option Compare Binary.

In that case, if you attempt to perform a simple comparison between

and

you’ll get a False return value. If you’re working with strings and performing

comparisons, make sure you’re aware of the Option Compare setting for the

module.

Comparison Operators

You can use the simple logical operators to compare two strings, like this:

If strText1 < strText2 Then...

In this case, VBA performs a character-by-character comparison according to the

Option Compare setting in force in the current module. The result of the compari-

son will most likely change, based on that setting. You can use the set of simple

comparison operators shown here.

In addition, VBA supplies the Like operator for comparing two strings. This

operator allows you to specify wildcards, character lists, and character ranges in

the comparison string, not just fixed characters. The following is a listing of all the

options for the comparison string using the Like operator:

Operator

Description

Less than

Less than or equal to

Greater than or

equal to

Equal to

Not equal to

Characters in Pattern

Matches in String

Any single character

Zero or more characters

Any single digit (0–9)

[charlist]

Any single character in

charlist

[!charlist]

Any single character not in

charlist

Chapter 1

•

Manipulating Strings

The string containing the wildcard information must be on the right-hand side of

the Like operator. That is, unlike many mathematical operators, this one is not

commutative: The order of the operands is significant.

For example, the following code fragment would compare a string with a

template that checks for valid Canadian Postal codes:

strTemp = "W1F 8G7"

If strTemp Like "[A-Z]#[A-Z] #[A-Z]#" Then

' You know strTemp is a valid Canadian Postal Code

End If

To check whether the single character in strTemp was a vowel, you could use

this expression:

If strTemp Like "[AEIOUaeiou]*" Then

' You know the first character in strTemp is a vowel

End If

If you want to see whether the word stored in strTemp doesn’t start with a

vowel, you could use an expression like this:

If strTemp Like "[!AEIOUaeiou]*" Then

' You know the word in strTemp doesn’t start with a vowel

End If

You’ll find the Like operator to be invaluable when you need to validate input.

Rather than parse the string yourself, you can use wildcards to allow various

ranges of characters.

The behavior of the Like operator depends on the Option Compare setting. Unless

you specify otherwise, each module uses Option Compare Binary (case-sensitive

comparisons).

There are a number of issues you need to be aware of when using the Like

operator (sorting, order of the characters within the range, and so on). Be sure to

check out the online help for this topic for more information.

Using Built-In String Functions

Using the StrComp Function

The StrComp function provides a way for you to compare strings, overriding the

Option Compare statement within a given module. To use StrComp, you specify

the two strings and a comparison method (binary, text, or database), and the func-

tion returns a value indicating how the two strings compared. In general, you call

StrComp like this:

intRetVal = StrComp(strText1, strText2, CompareOption)

The two text strings can be any string expressions. The CompareOption value

should be one of the items from Table 1.2 or a locale ID integer that specifies a

local sort order for comparisons. Depending on the parameters, StrComp returns

one of the values from Table 1.3.

The CompareOption parameter for StrComp is optional. If you omit it, VBA uses

the option selected by the Option Compare setting for the module. If you omit the

Option Compare, of course, VBA will use binary comparisons (vbBinaryCompare).

Online help incorrectly supplies a fourth value, not shown in Table 1.2 (vbUse-

CompareOption, –1). This value doesn’t appear to work in the current version of

VBA. For any function that takes a comparison option as a parameter, you may not

use the vbUseCompareOption value. (No matter what the online help tells you.)

TABLE 1.2:

Compare Options for StrComp

Constant

Option Compare Equivalent

vbBinaryCompare

Option Compare Binary

vbDatabaseCompare

Option Compare Database (Microsoft Access only)

vbTextCompare

Option Compare Text

TABLE 1.3:

Return Values for StrComp

StrComp Returns

strText1 is less than strText

–1

strText1 is equal to strText

strText1 is greater than strText2

Chapter 1

•

Manipulating Strings

Using the StrComp function, even if you normally perform case-sensitive com-

parisons, you can override that requirement for one comparison:

If StrComp(strText1, strText2, vbTextCompare) = 0 Then

' You know that strText1 and strText2 are the same, as far

' as the text comparison goes.

End If

Converting Strings

Rather than provide individual functions to convert strings from one format to

another, VBA includes the single StrConv function. This function allows you to

specify a string, as well as a conversion parameter indicating the conversion you’d

like to make. In general, you call the function like this:

strOutput

= StrConv(

strInput

Conversion, [LocaleID]

)

where

strInput

is the string to be converted;

Conversion

is a value from the follow-

ing table; and

LocaleID

(optionally) specifies the Windows LocaleID to use for the

conversion. (If you don’t specify a locale ID, VBA will use the current locale’s

information in order to perform the conversion.) StrConv returns the converted

string as its return value.

As you can see, the StrConv function performs two basic tasks: converting the

case (upper, lower, proper) of strings and converting strings from ANSI to Uni-

code and back.

If you’re working in a Japanese or other Far East locale, you’ll want to check out

the options for StrConv that are available only in those locales. See the VBA online

help for more information.

Constant

Description

vbUpperCase

Converts the string to uppercase characters.

vbLowerCase

Converts the string to lowercase characters.

vbProperCase

Converts the first letter of every word in the string

to uppercase.

vbUnicode

Converts the string to Unicode using the default

code page of the system.

vbFromUnicode

Converts the string from Unicode to the default

code page of the system.

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