How can I set the specified character by index to empty character in Delphi6?
procedure TMainForm.Button1Click(Sender: TObject);
var i: integer;
s_ord_account : String[10];
begin
s_ord_account := '0930002930' ;
i := 1;
REPEAT
IF s_ord_account[i] = '0' THEN
s_ord_account[i] := '';
INC(i);
UNTIL (i=5) OR (s_ord_account[i] <> ' ');
MessageDlg(s_ord_account,mtError, mbOKCancel, 0);
yend;
When I try to execute this code I get an error
[Error] Main.pas(30): Incompatible types: 'Char' and 'String'
First of all it would make a lot of sense for you to stop using Turbo Pascal strings and use the native Delphi string type, string.
There is no such thing as an empty character. You can use the Delete function to remove a character from the string. A simpler approach would be to use the StringReplace function. That renders your code entirely needless.
{$APPTYPE CONSOLE}
uses
SysUtils;
var
s: string;
begin
s := StringReplace('0930002930', '0', '', [rfReplaceAll]);
Writeln(s);
end.
Output
93293
Related
In Delphi XE4 and above, we may write something like:
function TestAnsiCompatible(const aStr: string): Boolean;
begin
end;
string in Delphi XE4 is declared as UnicodeString. It may hold a unicode string.
If we do some type conversion:
function TestAnsiCompatible(const aStr: string): Boolean;
var a: AnsiString;
begin
a := aStr;
Result := a = aStr;
end;
Some compiler warnings should prompt:
[dcc32 Warning]: W1058 Implicit string cast with potential data loss from 'string' to 'AnsiString'
[dcc32 Warning]: W1057 Implicit string cast from 'AnsiString' to 'string'
Is there a much simple and neat way to test if aStr is fully compatible with AnsiString? Or we shall check character by characters:
function TestAnsiCompatible(const aStr: string): Boolean;
var C: Char;
begin
Result := True;
for C in aStr do begin
if C > #127 then begin
Result := False;
Break;
end;
end;
end;
All you have to do is type-cast away the warnings:
function TestAnsiCompatible(const aStr: string): Boolean;
var
a: AnsiString;
begin
a := AnsiString(aStr);
Result := String(a) = aStr;
end;
Which can be simplified to this:
function TestAnsiCompatible(const aStr: string): Boolean;
begin
Result := String(AnsiString(aStr)) = aStr;
end;
I used to check if String(a) = AnsiString(a), until I had a user who had transferred data from one PC to another, and that had a different codepage. Then the data could not be read back properly. Then I changed my definition of "safe" to "string is code page 1252" (as this is the region where most of my users are). Then when reading back my data, I know I have to convert the string back from code page 1252.
function StringIs1252(const S: UnicodeString): Boolean;
// returns True if a string is in codepage 1252 (Western European (Windows))
// Cyrillic is 1251
const
WC_NO_BEST_FIT_CHARS = $00000400;
var
UsedDefaultChar: BOOL; // not Boolean!!
Len: Integer;
begin
if Length(S) = 0 then
Exit(True);
UsedDefaultChar := False;
Len := WideCharToMultiByte(1252, WC_NO_BEST_FIT_CHARS, PWideChar(S), Length(S), nil, 0, nil, #UsedDefaultChar);
if Len <> 0 then
Result := not UsedDefaultchar
else
Result := False;
end;
But if you want to check if your string can safely be converted to ansi - completely independent of the code page that is used when writing or reading, then you should check if all characters are in the range from #0..#127.
With Delphi XE4, try the following code:
procedure TForm3.Button1Click(Sender: TObject);
var
myStr: string;
begin
Edit1.Text := TPerlRegEx.EscapeRegExChars('test');
end;
The result (Edit1.Text) is empty.
Is this a bug or I'm missing something? I previously had no problem with this TPerlRegEx.EscapeRegExChars function with the version from regular-expressions.info pre-DelphiXE.
Update 2: Just upgrading an app written in D2010 and encountering this bug, but just wondering how such an obvious bug can exist this long... now I'm seriously considering making my code compatible to Free Pascal, but I really like the antonymous method...
Update 1: I'm using Delphi XE4 Update 1.
It appears to be a bug. If that's the case, both the XE4 and XE5 versions contain it. I've opened a QC report to report it for XE4..XE6.
The problem appears to be with the last line of the function:
Result.Create(Tmp, 0, J);
Stepping through in the debugger shows that the Tmp (a TCharArray) correctly contains 't','e','s','t', #0, #0, #0, #0 at that point, yet Result contains '' when the function actually returns, as setting a breakpoint on the end; following that line indicates that result contains '' at that point (and when the function returns).
Providing a replacement version in a class helper with a minor change to actually store the return value from the call to Create fixes the problem:
type
TPerlRegExHelper = class helper for TPerlRegEx
public
class function EscapeRegExCharsEx(const S: string): string; static;
end;
class function TPerlRegExHelper.EscapeRegExCharsEx(const S: string): string;
var
I, J: Integer;
Tmp: TCharArray;
begin
SetLength(Tmp, S.Length * 2);
J := 0;
for I := Low(S) to High(S) do
begin
case S[I] of
'.', '[', ']', '(', ')', '?', '*', '+', '{', '}', '^', '$', '|', '\':
begin
Tmp[J] := '\';
Inc(j);
Tmp[J] := S[I];
end;
#0:
begin
Tmp[J] := '\';
Inc(j);
Tmp[J] := '0';
end;
else
Tmp[J] := S[I];
end;
Inc(J);
end;
{ Result.Create(Tmp, 0, J); } // The problem code from the original
Result := String.Create(Tmp, 0, J);
end;
The XE3 (and the open-source version you mention) implement the logic totally differently, using the more standard manipulation of Result beginning at the first line of the function with Result := S;, and then using System.Insert as needed to add room for the escape characters.
This is a bug introduced in the XE4 release that is still present in XE6. Previous versions were fine. It looks like the changes were made in readiness for some future switch to immutable strings.
Rather ironically the bug is caused by the string never being assigned a value at all. It's one thing to set out not to mutate a string, but quite another never to initialize it!
So to the analysis of the bug. The method in question in TPerlRegEx.EscapeRegExChars defined in the System.RegularExpressionsCore unit. This is a class function that returns a string. Its signature is:
class function EscapeRegExChars(const S: string): string;
The XE4 implementation makes but one reference to the result variable. As follows:
Result.Create(Tmp, 0, J);
Here, Tmp is an array of char containing the escaped text to be returned, and J is the length of that text.
So, it seems clear that the author intended for this code to assign to the function return variable Result. Sadly that does not occur. Why not? Well, the Create method being called is defined in the helper for string. This is TStringHelper defined in the System.SysUtils unit. There are three Create overloads and the one in play here is:
class function Create(const Value: array of Char; StartIndex: Integer;
Length: Integer): string; overload; static;
Note that this is a class static function. That means that it is not an instance method and has no Self pointer. So when called like this:
Result.Create(Tmp, 0, J);
It is simply a function call whose return value is ignored. It might appear that the result variable would be set but remember that this Create is a class static method. It therefore has no instance. The compiler simply uses the type of Result to resolve the method. The code is equivalent to:
string.Create(Tmp, 0, J);
Nothing more exciting than a call to a function whose return value is simply ignored. Defeated by the extended syntax that allows us to ignore function return values.
The fix to the code is simple enough. Replace that final line with
Result := string.Create(Tmp, 0, J);
You could apply the fix in a copy of the unit, and include that unit in your code. An alternative to that, my preferred option, is to use a code hook. Like this:
unit FixTPerlRegExEscapeRegExChars;
interface
implementation
uses
System.SysUtils, Winapi.Windows, System.RegularExpressionsCore;
procedure PatchCode(Address: Pointer; const NewCode; Size: Integer);
var
OldProtect: DWORD;
begin
if VirtualProtect(Address, Size, PAGE_EXECUTE_READWRITE, OldProtect) then
begin
Move(NewCode, Address^, Size);
FlushInstructionCache(GetCurrentProcess, Address, Size);
VirtualProtect(Address, Size, OldProtect, #OldProtect);
end;
end;
type
PInstruction = ^TInstruction;
TInstruction = packed record
Opcode: Byte;
Offset: Integer;
end;
procedure RedirectProcedure(OldAddress, NewAddress: Pointer);
var
NewCode: TInstruction;
begin
NewCode.Opcode := $E9;//jump relative
NewCode.Offset := NativeInt(NewAddress)-NativeInt(OldAddress)-SizeOf(NewCode);
PatchCode(OldAddress, NewCode, SizeOf(NewCode));
end;
function EscapeRegExChars(Self: TPerlRegEx; const S: string): string;
var
I, J: Integer;
Tmp: TCharArray;
begin
SetLength(Tmp, S.Length * 2);
J := 0;
for I := Low(S) to High(S) do
begin
case S[I] of
'.', '[', ']', '(', ')', '?', '*', '+', '{', '}', '^', '$', '|', '\':
begin
Tmp[J] := '\';
Inc(j);
Tmp[J] := S[I];
end;
#0:
begin
Tmp[J] := '\';
Inc(j);
Tmp[J] := '0';
end;
else
Tmp[J] := S[I];
end;
Inc(J);
end;
Result := string.Create(Tmp, 0, J);
end;
initialization
RedirectProcedure(#TPerlRegEx.EscapeRegExChars, #EscapeRegExChars);
end.
Add this unit to your project and the calls to TPerlRegEx.EscapeRegExChars will start working again.
{$APPTYPE CONSOLE}
uses
System.RegularExpressionsCore,
FixTPerlRegExEscapeRegExChars in 'FixTPerlRegExEscapeRegExChars.pas';
begin
Writeln(TPerlRegEx.EscapeRegExChars('test'));
Readln;
end.
Output
test
QC#124091
I am trying to validate a string, where by it can contain all alphebetical and numerical characters, aswell as the underline ( _ ) symbol.
This is what I tried so far:
var
S: string;
const
Allowed = ['A'..'Z', 'a'..'z', '0'..'9', '_'];
begin
S := 'This_is_my_string_0123456789';
if Length(S) > 0 then
begin
if (Pos(Allowed, S) > 0 then
ShowMessage('Ok')
else
ShowMessage('string contains invalid symbols');
end;
end;
In Lazarus this errors with:
Error: Incompatible type for arg no. 1: Got "Set Of Char", expected
"Variant"
Clearly my use of Pos is all wrong and I am not sure if my approach is even the correct way of going about it or not?
Thanks.
You will have to check every single character of the string, if it's contained in Allowed
e.g.:
var
S: string;
const
Allowed = ['A' .. 'Z', 'a' .. 'z', '0' .. '9', '_'];
Function Valid: Boolean;
var
i: Integer;
begin
Result := Length(s) > 0;
i := 1;
while Result and (i <= Length(S)) do
begin
Result := Result AND (S[i] in Allowed);
inc(i);
end;
if Length(s) = 0 then Result := true;
end;
begin
S := 'This_is_my_string_0123456789';
if Valid then
ShowMessage('Ok')
else
ShowMessage('string contains invalid symbols');
end;
TYPE TCharSet = SET OF CHAR;
FUNCTION ValidString(CONST S : STRING ; CONST ValidChars : TCharSet) : BOOLEAN;
VAR
I : Cardinal;
BEGIN
Result:=FALSE;
FOR I:=1 TO LENGTH(S) DO IF NOT (S[I] IN ValidChars) THEN EXIT;
Result:=TRUE
END;
If you are using a Unicode version of Delphi (as you seem to be), beware that a SET OF CHAR cannot contain all valid characters in the Unicode character set. Then perhaps this function will be useful instead:
FUNCTION ValidString(CONST S,ValidChars : STRING) : BOOLEAN;
VAR
I : Cardinal;
BEGIN
Result:=FALSE;
FOR I:=1 TO LENGTH(S) DO IF POS(S[I],ValidChars)=0 THEN EXIT;
Result:=TRUE
END;
but then again, not all characters (actually Codepoints) in Unicode can be expressed by a single character, and some characters can be expressed in more than one way (both as a single character and as a multi-character).
But as long as you constrain yourself within these limitations, one of the above functions should be useful. You can even include both, if you add an "OVERLOAD;" directive to the end of each function declaration, as in:
FUNCTION ValidString(CONST S : STRING ; CONST ValidChars : TCharSet) : BOOLEAN; OVERLOAD;
FUNCTION ValidString(CONST S,ValidChars : STRING) : BOOLEAN; OVERLOAD;
Lazarus/Free Pascal doesn't overload pos for that but has "posset" variants in unit strutils for that;
http://www.freepascal.org/docs-html/rtl/strutils/posset.html
Regarding Andreas' (IMHO correct ) remark, you can use isemptystr for that. It was meant to check for strings that only contain whitespace, but it basically checks if a string only contains characters in a set.
http://www.freepascal.org/docs-html/rtl/strutils/isemptystr.html
You can use Regular Expressions:
uses System.RegularExpressions;
if not TRegEx.IsMatch(S, '^[_a-zA-Z0-9]+$') then
ShowMessage('string contains invalid symbols');
I have written a Delphi function that loads data from a .dat file into a string list. It then decodes the string list and assigns to a string variable. The contents of the string use the '#' symbol as a separator.
How can I then take the contents of this string and then assign its contents to local variables?
// Function loads data from a dat file and assigns to a String List.
function TfrmMain.LoadFromFile;
var
index, Count : integer;
profileFile, DecodedString : string;
begin
// Open a file and assign to a local variable.
OpenDialog1.Execute;
profileFile := OpenDialog1.FileName;
if profileFile = '' then
exit;
profileList := TStringList.Create;
profileList.LoadFromFile(profileFile);
for index := 0 to profileList.Count - 1 do
begin
Line := '';
Line := profileList[Index];
end;
end;
After its been decoded the var "Line" contains something that looks like this:
example:
Line '23#80#10#2#1#...255#'.
Not all of the values between the separators are the same length and the value of "Line" will vary each time the function LoadFromFile is called (e.g. sometimes a value may have only one number the next two or three etc so I cannot rely on the Copy function for strings or arrays).
I'm trying to figure out a way of looping through the contents of "Line", assigning it to a local variable called "buffer" and then if it encounters a '#' it then assigns the value of buffer to a local variable, re-initialises buffer to ''; and then moves onto the next value in "Line" repeating the process for the next parameter ignoring the '#' each time.
I think I have been scratching around with this problem for too long now and I cannot seem to make any progress and need a break from it. If anyone would care to have a look, I would welcome any suggestions on how this might be achieved.
Many Thanks
KD
You need a second TStringList:
lineLst := TStringList.Create;
try
lineLst.Delimiter := '#';
lineLst.DelimitedText := Line;
...
finally
lineLst.Free;
end;
Depending on your Delphi version you can set lineLst.StrictDelimiter := true in case the line contains spaces.
You can do something like this:
program Project1;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils, StrUtils;
var
S : string;
D : string;
begin
S := '23#80#10#2#1#...255#';
for D in SplitString(S,'#') do //SplitString is in the StrUtils unit
writeln(D);
readln;
end.
You did not tag your Delphi version, so i don't know if it applies or not.
That IS version-specific. Please do!
In order of my personal preference:
1: Download Jedi CodeLib - http://jcl.sf.net. Then use TJclStringList. It has very nice split method. After that you would only have to iterate through.
function Split(const AText, ASeparator: string; AClearBeforeAdd: Boolean = True): IJclStringList;
uses JclStringLists;
...
var s: string; js: IJclStringList.
begin
...
js := TJclStringList.Create().Split(input, '#', True);
for s in js do begin
.....
end;
...
end;
2: Delphi now has somewhat less featured StringSplit routine. http://docwiki.embarcadero.com/Libraries/en/System.StrUtils.SplitString
It has a misfeature that array of string type may be not assignment-compatible to itself. Hello, 1949 Pascal rules...
uses StrUtils;
...
var s: string;
a_s: TStringDynArray;
(* aka array-of-string aka TArray<string>. But you have to remember this term exactly*)
begin
...
a_s := SplitString(input, '#');
for s in a_s do begin
.....
end;
...
end;
3: Use TStringList. The main problem with it is that it was designed that spaces or new lines are built-in separators. In newer Delphi that can be suppressed. Overall the code should be tailored to your exact Delphi version. You can easily Google for something like "Using TStringlist for splitting string" and get a load of examples (like #Uwe's one).
But you may forget to suppress here or there. And you may be on old Delphi,, where that can not be done. And you may mis-apply example for different Delphi version. And... it is just boring :-) Though you can make your own function to generate such pre-tuned stringlists for you and carefully check Delphi version in it :-) But then You would have to carefully free that object after use.
I use a function I've written called Fetch. I think I stole the idea from the Indy library some time ago:
function Fetch(var VString: string; ASeperator: string = ','): string;
var LPos: integer;
begin
LPos := AnsiPos(ASeperator, VString);
if LPos > 0 then
begin
result := Trim(Copy(VString, 1, LPos - 1));
VString := Copy(VString, LPos + 1, MAXINT);
end
else
begin
result := VString;
VString := '';
end;
end;
Then I'd call it like this:
var
value: string;
line: string;
profileFile: string;
profileList: TStringList;
index: integer;
begin
if OpenDialog1.Execute then
begin
profileFile := OpenDialog1.FileName;
if (profileFile = '') or not FileExists(profileFile) then
exit;
profileList := TStringList.Create;
try
profileList.LoadFromFile(profileFile);
for index := 0 to profileList.Count - 1 do
begin
line := profileList[index];
Fetch(line, ''''); //discard "Line '"
value := Fetch(line, '#')
while (value <> '') and (value[1] <> '''') do //bail when we get to the quote at the end
begin
ProcessTheNumber(value); //do whatever you need to do with the number
value := Fetch(line, '#');
end;
end;
finally
profileList.Free;
end;
end;
end;
Note: this was typed into the browser, so I haven't checked it works.
Here is another question about convert old code to D2009 and Unicode. I'm certain that there is simple but i don't see the solution...
CharacterSet is a set of Char and s[i] should also be a Char.
But the compiler still think there is a conflict between AnsiChar and Char.
The code:
TSetOfChar = Set of Char;
procedure aFunc;
var
CharacterSet: TSetOfChar;
s: String;
j: Integer;
CaseSensitive: Boolean;
begin
// Other code that assign a string to s
// Set CaseSensitive to a value
CharacterSet := [];
for j := 1 to Length(s) do
begin
Include(CharacterSet, s[j]); // E2010 Incompatible types: 'AnsiChar' and 'Char'
if not CaseSensitive then
begin
Include(CharacterSet, AnsiUpperCase(s[j])[1]);
Include(CharacterSet, AnsiLowerCase(s[j])[1])
end
end;
end;
Because a Pascal set can't have a range higher than 0..255, the compiler quietly converts sets of chars to sets of AnsiChars. That's what's causing trouble for you.
There is no good and simple answer to the question (the reason is already given by Mason). The good solution is to reconsider the algoritm to get rid off "set of char" type. The quick and dirty solution is to preserve ansi chars and strings:
TSetOfChar = Set of AnsiChar;
procedure aFunc;
var
CharacterSet: TSetOfChar;
s: String;
S1, SU, SL: Ansistring;
j: Integer;
CaseSensitive: Boolean;
begin
// Other code that assign a string to s
// Set CaseSensitive to a value
S1:= s;
SU:= AnsiUpperCase(s);
SL:= AnsiLowerCase(s);
CharacterSet := [];
for j := 1 to Length(S1) do
begin
Include(CharacterSet, S1[j]);
if not CaseSensitive then
begin
Include(CharacterSet, SU[j]);
Include(CharacterSet, SL[j]);
end
end;
end;
Delphi does not support sets of Unicode characters. You can only use AnsiChar in a set, but that's not big enough to fit all the possible characters your string might hold.
Instead of Delphi's native set type, though, you can use the TBits type.
procedure aFunc;
var
CharacterSet: TBits;
s: String;
c: Char;
CaseSensitive: Boolean;
begin
// Other code that assign a string to s
// Set CaseSensitive to a value
CharacterSet := TBits.Create;
try
for c in s do begin
CharacterSet[Ord(c)] := True;
if not CaseSensitive then begin
CharacterSet[Ord(Character.ToUpper(c))] := True;
CharacterSet[Ord(Character.ToLower(c))] := True;
end
end;
finally
CharacterSet.Free;
end;
end;
A TBits object automatically expends to accommodate the highest bit it needs to represent.
Other changes I made to your code include using the new "for-in" loop style, and the new Character unit for dealing with Unicode characters.