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String Functions and Manipulation in VB6 including common functions such as Asc, Chr, Mid, Join, LSet, StrConv, StrReverse, Filter, Replace == 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$(What, i, 1), "") next i End Function === Reverse (function) === New in VB6. To reverse a string. === Split (function) === New in VB6 Split a string into a variant array. === StrComp (function) === Returns a Variant (Integer) indicating the result of a string comparison. Syntax :StrComp(string1, string2[, compare]) Return Values If StrComp returns string1 is less than string2 -1 string1 is equal to string2 0 string1 is greater than string2 1 string1 or string2 is Null Null == Performance Rating == table 1 {| class="stylish" |+ Relative performance of VB6 string functions |- ! Function ! Performance ! Description |- | Len | class="num" | 1 | Len(S) returns the number of ''characters'' in string S.<br />''(Note: works differently with UDTs)'' |- | LenB | class="num" | 1 | LenB(S) returns the number of ''bytes'' in S. |- | AscW | class="num" | 1 | AscW(S) returns the ''Unicode value'' of the first character in S. |- | AscB | class="num" | 1 | AscB(S) returns the ''first byte'' in S. |- | Asc | class="num" | 7 | Asc(S) returns the ''ANSI value'' of the first character in S. |- | ChrW$ | class="num" | 17 | ChrW$(U) returns a string containing the ''Unicode character'' U. |- | ChrB$ | class="num" | 18 | ChrB$(B) returns a ''byte string'' containing the ''character'' B. |- | Chr$ | class="num" | 24 | Chr$(A) returns a string containing the ''ANSI character'' A. |- | Left$ | class="num" | 18 | Left$(S,x) returns x characters from the ''start'' of S. |- | Right$ | class="num" | 21 | Right$(S,x) returns x characters from the ''end'' of S. |- | Mid$ | class="num" | 24 | Mid$(S,x,y) returns y characters from S, starting at the ''x'th'' character. |- | CStr | class="num" | 36 | CStr(x) returns the string representation of x (localized). |- | Str$ | class="num" | 111 | Str$(x) returns the string representation of x (not localized). |} How to read the table: Calling Len takes 1 unit of time, while Asc takes 7 units. You can call Len 7 times in the same time you call Asc once. table 2 <TABLE CLASS="stylish"> <CAPTION>Relative performance of VB6 string functions</CAPTION> <TR> <TH>Function</TH><TH>Performance</TH><TH>Description</TH> </TR> <TR> <TD>LTrim$</TD><TD CLASS="num">20</TD><TD>LTrim$(S) returns a copy of S without <EM>leading</EM> spaces.</TD> </TR> <TR> <TD>RTrim$</TD><TD CLASS="num">21</TD><TD>RTrim$(S) returns a copy of S without <EM>trailing</EM> spaces.</TD> </TR> <TR> <TD>Trim$</TD><TD CLASS="num">29</TD><TD>Trim$(S) returns a copy of S without <EM>leading or trailing</EM> spaces.</TD> </TR> <TR> <TD>Val</TD><TD CLASS="num">89</TD><TD>Val(S) returns the numeric value contained in S (non-localized).</TD> </TR> <TR> <TD>CInt</TD><TD CLASS="num">81</TD><TD>CInt(S) returns the integer value contained in S (localized, rounded).</TD> </TR> <TR> <TD>CDbl</TD><TD CLASS="num">103</TD><TD>CDbl(S) returns the double floating point value contained in S (localized).</TD> </TR> <TR> <TD>LCase$</TD><TD CLASS="num">53</TD><TD>LCase$(S) returns a copy of S with <EM>lower case letters</EM>.</TD> </TR> <TR> <TD>UCase$</TD><TD CLASS="num">53</TD><TD>UCase$(S) returns a copy of S with <EM>upper case letters</EM>.</TD> </TR> <TR> <TD>StrConv(vbLowerCase)</TD><TD CLASS="num">327</TD><TD>StrConv(S,vbLowerCase) returns a copy of S with <EM>lower case letters</EM>.</TD> </TR> <TR> <TD>StrConv(vbUpperCase)</TD><TD CLASS="num">333</TD><TD>StrConv(S,vbUpperCase) returns a copy of S with <EM>upper case letters</EM>.</TD> </TR> <TR> <TD>StrComp(vbBinaryCompare)</TD><TD CLASS="num">47</TD><TD>StrComp(S1,S2,vbBinaryCompare) compares string S1 and S2 based on their <EM>Unicode values</EM>.</TD> </TR> <TR> <TD>StrComp(vbTextCompare)</TD><TD CLASS="num">65</TD><TD>StrComp(S1,S2,vbTextCompare) compares string S1 and S2 in a <EM>locale-dependent, case-insensitive way</EM>.</TD> </TR> <TR> <TD>InStr(vbBinaryCompare)</TD><TD CLASS="num">14</TD><TD>InStr(x,S1,S2,vbBinaryCompare) looks for S2 in S1, starting at position x, in a <EM>locale-independent, case-sensitive way</EM>.</TD> </TR> <TR> <TD>InStr(vbTextCompare)</TD><TD CLASS="num">156</TD><TD>InStr(x,S1,S2,vbTextCompare) looks for S2 in S1, starting at position x, using <A HREF="instr.html#vbtextcompare">text comparison</A>.</TD> </TR> <TR> <TD><b style="color:black;background-color:#a0ffff">InStrRev</b>(vbBinaryCompare)</TD><TD CLASS="num">69</TD><TD><b style="color:black;background-color:#a0ffff">InStrRev</b>(S1,S2,x,vbBinaryCompare) looks for S2 in S1, from position x back to 1, in a <EM>locale-independent, case-sensitive way</EM>.</TD> </TR> <TR> <TD><b style="color:black;background-color:#a0ffff">InStrRev</b>(vbTextCompare)</TD><TD CLASS="num">193</TD><TD><b style="color:black;background-color:#a0ffff">InStrRev</b>(S1,S2,x,vbTextCompare) looks for S2 in S1, from position x back to 1, using <A HREF="instr.html#vbtextcompare">text comparison</A>.</TD> </TR> <TR> <TD><b style="color:black;background-color:#99ff99">Replace</b>(vbBinaryCompare)</TD><TD CLASS="num">375</TD><TD><b style="color:black;background-color:#99ff99">Replace</b>(S1,S2,S3,x,y,vbBinaryCompare) replaces S2 with S3 in S1, starting at position x, max y times, in a <EM>locale-independent, case-sensitive way</EM>.</TD> </TR> <TR> <TD><b style="color:black;background-color:#99ff99">Replace</b>(vbTextCompare)</TD><TD CLASS="num">513</TD><TD><b style="color:black;background-color:#99ff99">Replace</b>(S1,S2,S3,x,y,vbBinaryCompare) replaces S2 with S3 in S1, starting at position x, max y times, using <EM>text comparison</EM>.</TD> </TR> </TABLE> Reference: http://www.aivosto.com/vbtips/stringopt2.html &nbsp; == 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, however, will appear as a 0 in a database numeric field after write. * '''Empty''': Also appears as a 0 in a database numeric field after write. * '''Nothing''': &nbsp; &nbsp; [[Category:Computer Technology]] [[Category:Programming]] [[Category:VB6]]

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