Difference between revisions of "String Functions and Manipulation in VB6"
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Use the NULL keyword to assign Null to a recordset field, use the IsNull function to test if a recordset fields contains Null. | Use the NULL keyword to assign Null to a recordset field, use the IsNull function to test if a recordset fields contains Null. | ||
| − | vbNullString: The same as "", as in an empty string. It is more efficient to use vbNullString though. use it instead of "" | + | * '''vbNullString''': The same as "", as in an empty string. It is more efficient to use vbNullString though. use it instead of "" |
| − | vbNull: This is supposed to be NULL but actually equals 1. | + | * '''vbNull''': This is supposed to be NULL but actually equals 1. |
| − | vbNullChar: | + | * '''vbNullChar''': |
| − | Null: Used for writing NULL in SQL standard, a NULL to the database, which will appear as a 0 in a numeric field. | + | * '''Null''': Used for writing NULL in SQL standard, a NULL to the database, which will appear as a 0 in a numeric field. |
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Revision as of 15:14, 15 February 2008
String Functions and Manipulation in VB6 including common functions such as Asc, Chr, Mid, Join, LSet, StrConv, StrReverse, Filter, Replace
Contents
Functions and Description
Asc (function)
Returns an Integer representing the character code corresponding to the first letter in a string.
Syntax
- Asc(string)
Chr (function)
Returns a String containing the character associated with the specified character code.
Syntax
- Chr(charcode)
InStr (function)
Returns a Variant (Long) specifying the position of the first occurrence of one string within another.
Syntax
- InStr([start, ]string1, string2[, compare])
Example
Dim SearchString, SearchChar, MyPos SearchString ="XXpXXpXXPXXP" ' String to search in. SearchChar = "P" ' Search for "P". ' A textual comparison starting at position 4. Returns 6. MyPos = Instr(4, SearchString, SearchChar, 1) ' A binary comparison starting at position 1. Returns 9. MyPos = Instr(1, SearchString, SearchChar, 0) ' Comparison is binary by default (last argument is omitted). MyPos = Instr(SearchString, SearchChar) ' Returns 9. MyPos = Instr(1, SearchString, "W") ' Returns 0.
InStrRev (function)
New in VB6.
Similar to InStr but searches from end of string. Returns the position of an occurrence of one string within another, from the end of string.
Syntax
- InstrRev(stringcheck, stringmatch[, start[, compare]])
Join (function)
New in VB6
Used to join arrays elements.
Mid (function)
Returns a Variant (String) containing a specified number of characters from a string.
Syntax
- Mid(string, start[, length])
Replace (function)
New in VB6.
Returns a string in which a specified substring has been replaced with another substring a specified number of times.
Syntax
- Replace(expression, find, replace[, start[, count[, compare]]])
Example
Debug.print Replace("abababa", "a", "")
Example
public Function StripOut(From as string, What as string) as string
Dim i as Integer
StripOut = From
for i = 1 to len(What)
StripOut = Replace(StripOut, mid$(What, i, 1), "")
next i
End Function
Reverse (function)
New in VB6.
To reverse a string.
Split (function)
New in VB6
Split a string into a variant array.
StrComp (function)
Returns a Variant (Integer) indicating the result of a string comparison.
Syntax
- StrComp(string1, string2[, compare])
Return Values
If StrComp returns string1 is less than string2 -1 string1 is equal to string2 0 string1 is greater than string2 1 string1 or string2 is Null Null
Performance Rating
table 1
| Function | Performance | Description |
|---|---|---|
| Len | 1 | Len(S) returns the number of characters in string S. (Note: works differently with UDTs) |
| LenB | 1 | LenB(S) returns the number of bytes in S. |
| AscW | 1 | AscW(S) returns the Unicode value of the first character in S. |
| AscB | 1 | AscB(S) returns the first byte in S. |
| Asc | 7 | Asc(S) returns the ANSI value of the first character in S. |
| ChrW$ | 17 | ChrW$(U) returns a string containing the Unicode character U. |
| ChrB$ | 18 | ChrB$(B) returns a byte string containing the character B. |
| Chr$ | 24 | Chr$(A) returns a string containing the ANSI character A. |
| Left$ | 18 | Left$(S,x) returns x characters from the start of S. |
| Right$ | 21 | Right$(S,x) returns x characters from the end of S. |
| Mid$ | 24 | Mid$(S,x,y) returns y characters from S, starting at the x'th character. |
| CStr | 36 | CStr(x) returns the string representation of x (localized). |
| Str$ | 111 | Str$(x) returns the string representation of x (not localized). |
How to read the table: Calling Len takes 1 unit of time, while Asc takes 7 units. You can call Len 7 times in the same time you call Asc once.
table 2
| Function | Performance | Description |
|---|---|---|
| LTrim$ | 20 | LTrim$(S) returns a copy of S without leading spaces. |
| RTrim$ | 21 | RTrim$(S) returns a copy of S without trailing spaces. |
| Trim$ | 29 | Trim$(S) returns a copy of S without leading or trailing spaces. |
| Val | 89 | Val(S) returns the numeric value contained in S (non-localized). |
| CInt | 81 | CInt(S) returns the integer value contained in S (localized, rounded). |
| CDbl | 103 | CDbl(S) returns the double floating point value contained in S (localized). |
| LCase$ | 53 | LCase$(S) returns a copy of S with lower case letters. |
| UCase$ | 53 | UCase$(S) returns a copy of S with upper case letters. |
| StrConv(vbLowerCase) | 327 | StrConv(S,vbLowerCase) returns a copy of S with lower case letters. |
| StrConv(vbUpperCase) | 333 | StrConv(S,vbUpperCase) returns a copy of S with upper case letters. |
| StrComp(vbBinaryCompare) | 47 | StrComp(S1,S2,vbBinaryCompare) compares string S1 and S2 based on their Unicode values. |
| StrComp(vbTextCompare) | 65 | StrComp(S1,S2,vbTextCompare) compares string S1 and S2 in a locale-dependent, case-insensitive way. |
| InStr(vbBinaryCompare) | 14 | InStr(x,S1,S2,vbBinaryCompare) looks for S2 in S1, starting at position x, in a locale-independent, case-sensitive way. |
| InStr(vbTextCompare) | 156 | InStr(x,S1,S2,vbTextCompare) looks for S2 in S1, starting at position x, using <A HREF="instr.html#vbtextcompare">text comparison</A>. |
| InStrRev(vbBinaryCompare) | 69 | InStrRev(S1,S2,x,vbBinaryCompare) looks for S2 in S1, from position x back to 1, in a locale-independent, case-sensitive way. |
| InStrRev(vbTextCompare) | 193 | InStrRev(S1,S2,x,vbTextCompare) looks for S2 in S1, from position x back to 1, using <A HREF="instr.html#vbtextcompare">text comparison</A>. |
| Replace(vbBinaryCompare) | 375 | Replace(S1,S2,S3,x,y,vbBinaryCompare) replaces S2 with S3 in S1, starting at position x, max y times, in a locale-independent, case-sensitive way. |
| Replace(vbTextCompare) | 513 | Replace(S1,S2,S3,x,y,vbBinaryCompare) replaces S2 with S3 in S1, starting at position x, max y times, using text comparison. |
Reference: http://www.aivosto.com/vbtips/stringopt2.html
Null, 0, and Empty Strings
In VB, Null is a subtype of a Variant, in the same way the Empty is also. In other words, Null and Empty are both special states of a Variant variable.
vbNull and vbEmpty are the codes returned from the VarType function when applied to a value of that type, e.g.
VarType(Empty) = vbEmpty VarType(Null) = vbNull
This provides one method of testing whether a value is Null or Empty. The other is by calling the IsNull and IsEmpty functions.
In a database, NULL has a similar status to Null is VB Variants, although it's defined by the SQL standard rather than the VB language.
Use the NULL keyword to assign Null to a recordset field, use the IsNull function to test if a recordset fields contains Null.
- vbNullString: The same as "", as in an empty string. It is more efficient to use vbNullString though. use it instead of ""
- vbNull: This is supposed to be NULL but actually equals 1.
- vbNullChar:
- Null: Used for writing NULL in SQL standard, a NULL to the database, which will appear as a 0 in a numeric field.
