Crash in Delphi function - StrToDateTime - delphi

Who can to advice in my problem.
I set date format as 'JUL/12 - 12 15:35', but when using StrToDateTime then give EConvertError.
What can I do with this format which contains 2 - date separator ?
Use next code
function LocaleFormatStrToDateTime(const S: string): TDateTime;
var
LFormatSettings: TFormatSettings;
begin
LFormatSettings := GetLocaleFormatSettings(LOCALE_SYSTEM_DEFAULT);
LFormatSettings.ShortTimeFormat := FormatSettings.ShortTimeFormat;
LFormatSettings.TimeSeparator := FormatSettings.TimeSeparator;
Result := StrToDateTime(S, LFormatSettings);
end;
----------
**
the best solution is use jvDateUtil.StrToDate*
**

Your format is completely non-standard (and almost incomprehensible), so can't be handled by the built-in Date/Time formatters.
You've designed your own format, so you need to write your own code to convert to and from it.
This is nature's way of telling you not to use wacky date and time formats!

Probably the string you're trying to convert is not compatible with the default system format. Taking a look at the method signature and description reveals that you can override it to suit your needs, see an example here.
It would be helpful if you posted a piece of the code you have so far, maybe you overlooked something.
EDIT
I've missed the fact that your're using a complex format, including multiple separators for the date, which I'm not sure that are supported in delphi.
I guess that in this case you could split your string into pieces and then encode them into a TDateTime. To convert your month name to a month number you can iterate through the LFormatSettings.ShortMonthNames array, something like:
String longMonth:= copy(S, 0, 3);
for i := Low(LFormatSettings.ShortMonthNames) to High(LFormatSettings.ShortMonthNames) do
if SameText(longMonth, LFormatSettings.ShortMonthNames[i]) then begin
shortMonth:=FormatFloat('00', i);
Break;
end;

Related

Convert Array of ShortInt to String, Delphi

I'm doing the way I learned, that is:
with a FOR and taking the Index array one by one, but it is leaving too slow, would otherwise convert it to a String? that leaves quicker?
In my case it would be a Dynamic Array of ShortInt.
For example, given this input:
[0,20,-15]
I would like the following output:
0,20,-15
I suspect that your code is slow because it is performing unnecessary reallocations of the string. However, without seeing your code it's hard to be sure.
Probably the simplest way to code your algorithm is to use TStringBuilder. Whether or not that gives sufficient performance, only you can say.
sb := TStringBuilder.Create;
try
for i := 0 to high(buffer) do
begin
sb.Append(IntToStr(buffer[i]));
if i<high(buffer) then
sb.Append(',');
end;
str := sb.ToString;
finally
sb.Free;
end;

Is it OK to use DecimalSeparator to force Floattostr/Strtofloat functions to use a decimal point

Currently, I'm setting DecimalSeparator to a '.' in each procedure which uses these functions.
It would be much easier to set this globally at the start of the program but I found Delphi seems to periodically set this back to the current locale.
I need to make sure that a decimal point is used for all conversions no matter which country the program is used in as this is the standard for this type of program and all files structure and communication protocols, numeric displays in forms/edits etc are required to be formatted in this way.
I've been told in another thread that using decimalseparator is not the correct way to do it but I was not given any alternatives. The other threads concerning this subject that I've read don't seem to offer any formative guidance or are overly complex.
Is there a simple 'correct' way to do this ?
Yes, the DecimalSeparator global variable might be changed by the RTL during runtime, which caused a lot of headache for me a few years ago before I realised this.
The thing is that DecimalSeparator is updated by the RTL when the Windows decimal separator is changed, for instance, using the Control Panel. This might seem like a rather small problem. Indeed, how often does the end user change the system's decimal separator?
The big issue is that the DecimalSeparator variable is updated (according to the system setting) every time you switch user (in Windows). That came as a surprise to me. That is, if your system setting uses a comma (',') as the decimal separator, and you set DecimalSeparator := '.' at application startup, then DecimalSeparator will revert to a comma if you switch user (and you'll notice that when you switch back).
You can tell the RTL not to update the decimal separator by
Application.UpdateFormatSettings := false;
At any rate, there are better alternatives to DecimalSeparator, as discussed in other answers and comments.
I am/was under the assumption that the global DecimalSeperator variable would not be touched by the RTL. If not, then all these routines have an optional parameter FormatSettings which you could use. Globaly declare a TFormatSettings variable and use it for each occurance of these routines.
A small benefit of it could be that the routines are thread-safe when you specify your own format settings.
To be on the safe side, i would use TFormatSettings, this has two advantages:
The formatting is thread safe, other code/libraries cannot influence your function.
You do not influence other code, which possibly rely upon certain settings.
Here a possible implementation:
function FloatToStrWithDecimalPoint(const Value: Extended; const Format: String = '0.###'): String;
var
myFormatSettings: TFormatSettings;
begin
GetLocaleFormatSettings(GetThreadLocale, myFormatSettings);
myFormatSettings.DecimalSeparator := '.';
Result := FormatFloat(Format, Value, myFormatSettings);
end;
You could patch every string before and after calling a RTL function with some ForceLocalSeparator() and ForceDotSeparator() functions.
// before a RTL call
Function ForceLocalSeparator(Const StrValue: String): String;
Var
SepPos: Integer;
Begin
Result := StrValue;
If DecimalSeparator <> '.' Then
Begin
SepPos := Pos( '.', Result );
If SepPos > 0 Then Result[SepPos] := DecimalSeparator;
End;
End;
// after a RTL call
Function ForceDotSeparator(Const StrValue: String): String;
Var
SepPos: Integer;
Begin
Result := StrValue;
If DecimalSeparator <> '.' Then
Begin
SepPos := Pos( DecimalSeparator, Result );
If SepPos > 0 Then Result[SepPos] := '.';
End;
End;
It's OK if you have no alternative. Prefer the versions of those functions that accept a TFormatSettings parameter, if your Delphi version is recent enough, so that you don't interfere with any other code that relies on that global variable for locale-aware behavior.
FloatToStr and StrToFloat are locale-sensitive functions. If you need to convert your floating-point value to a string to persist it somewhere that a program will read later (such as to a file, the registry, or a network socket), then you should use the locale-independent functions Str and Val for your conversions instead. They always use . for the decimal separator, regardless of the DecimalSeparator variable or other environmental settings.

Avoiding Locale Conflicts when storing TDateTime's in Floats?

I got the TDateTime thing fixed by using Floating vars to store them in a file. However, now I face a new problem: Invalid Floating Point - Most likely because of the Comma Separator.
How can I set the default separator in my program? Or is there any other way around?
You can use a TFormatSettings record to specify the decimal separator when you call StrToFloat and FloatToStr. You have to decide what to use and stick to that. Here is sample code with a .
var
d: TDateTime;
s: string;
fs: TFormatSettings;
begin
d := Now();
fs.DecimalSeparator := '.';
s := FloatToStr(d, fs);
end;
Another option would be to use the XML standard date time format. Delphi has some functions in XSBuiltIns to do the conversion from TDateTime to string and back. You will have a time zone offset in the value so if you move your persisted TDateTime from one time zone to another you may have some unwanted behavior. It depends on the usage of the value.
var
d: TDateTime;
s: string;
begin
d := Now();
s := DateTimeToXMLTime(d);
d := XMLTimeToDateTime(s);
end;
As Mikael suggested, there are a many ways to do this. To re-cap you wish to store a TDateTime to a file in textual format and be able to restore this value successfully irrespective of the locale on which the restoration happens.
Option 1
When storing, call FloatToStr, say, but force a '.' for the decimal separator through the TFormatSettings parameter. On restore, use StrToFloat with the same TFormatSettings.
Option 2
Encode the 8 byte TDateTime value using base 64. This has the downside that it renders the value unreadable.
Option 3
Similar to option 1, but encode the TDateTime by calling DateTimeToStr and explicitly passing a TFormatSettings that does not rely on anything in the locale – so do not rely on the locale's date or time separators, instead force your own. To reverse call StrToDateTime with an identical TFormatSettings record.

How to get the first element in a string?

I'm trying to figure out a way to check a string's first element if it's either a number or not.
if not(myString[0] in [0..9]) then //Do something
The problem is that I get an error "Element 0 inaccessible - use 'Length' or 'SetLength"
Another way came to my head from my C-like exprieince - convert the first element of the string to char and check the char,but there is no difference in the compile errors.
if not(char(myString[0]) in [0..9]) then //Do something
How do I accomplish it?
Strings are 1-based:
if not (myString[1] in ['0'..'9']) then // Do something
Pascal and Delphi indexes string from 1. This is a legacy from time where zero byte contained length, while next 255 (index 1 to 255) contained actual characters.
Joel Spolsky wrote quite good article on string issues:
http://www.joelonsoftware.com/articles/fog0000000319.html
Delphi strings use a 1-based index, so just rewrite to
if not(myString[1] in ['0'..'9']) then //Do something
Also take note of the quotes around the 0..9, otherwise you would be comparing characters to integers.
We should keep in mind some things:
String in Delphi is 0-based for mobile platforms and 1-based for Windows.
String in old versions of Delphi is AnsiString (1-byte per char) and WideString in new versions (2-bytes per char).
Delphi supports set of AnsiChar, but doesn't support set of WideChar.
So if we want to write a code compatible with all versions of Delphi, then it should be something like this:
if (myString[Low(myString)]>='0') and (myString[Low(myString)]<='9') then
// Do something
if not(myString[0] in [0..9]) then //Do something
If you're using Delphi 2009, the TCharacter class in Character.pas has functions like IsDigit to help simplify these kinds of operations.
Once you fix the indexing, of course. :)
With later updates to Delphi mobile code, the bottom string index changed from 0 to 1. When you compile older programmes, they compile and run correctly using 0 starting index. Programmes created with the later IDE produce an error. When you have mixtures, life gets complex!
It would be good to be able to take an older programme and tell the IDE that you want it brought up to date (maybe this would fix other things, like fonts getting scrambled when you answer a phone call!) but it would be good to get things consistent!
The simplest way to check to see if the first character of string is an integer, and then dispatch:
var
iResult : integer;
begin
if TryStrToInt( mySTring[1], iResult) then
begin
// handle number logic here iResult = number
end
else
begin
// handle non number logic here
end;
end;
I use a utility function to test the entire string:
function IsNumeric(const Value: string): Boolean;
var
i: Integer;
begin
Result := True;
for i := 1 to Length(Value) do
if not (Value[i] in ['0'..'9','.','+','-']) then
begin
Result := False;
Break;
end;
end;
The above code is for Delphi versions prior to 2007. In 2007 and 2009, you could change the integer variable i to a character c, and use for c in Value instead.
To test for integers only, remove the '.' from the set of characters to test against.
This is incorrect. ISO strings and older Pascal's also started at one. It is just a general convention, and afaik the s[0] thing is a result of that being vacant, and cheap to code in the UCSD bytecode interpreter. But that last bit is before my time, so only my guessing.
It results from the Pascal ability to have arbitrary upper and lower bounds, which provides for more typesafety accessing arrays.
Really old Pascal strings (till early eighties) strings were even worse than C ones btw. Multiple conventions were in used, but all were based on static arrays (like early C), but they were typically space padded, so you had scan back from the end till the spaces ended.
(removed the legacy tag, since being 1 based is not legacy. Accessing s[0] as length IS legacy, but that is not what the question is about)
Foreach element in strName
if not element in [0-9] then
do something
else
element is a digit
end if
Don't forget the quote between digits number.

Getting a Field List from a DBExpress TSQLQuery

I am having a problem getting a list of fields from a query defined at run time by the users of my program. I let my users enter a SQL query into a memo control and then I want to let them go through the fields that will return and do such things as format the output, sum column values and so forth. So, I have to get the column names so they have a place to enter the additional information.
I would do fine if there were no parameters, but I also have to let them define filter parameters for the query. So, if I want to set the parameters to null, I have to know what the parameter's datatype is.
I am using Delphi 2006. I connect to a Firebird 2.1 database using the DBExpress component TSQLConnection and TSQLQuery. Previously, I was successful using:
for i := 0 to Qry.Params.Count - 1 do Qry.Params[i].value := varNull;
I discovered I had a problem when I tried to use a date parameter. It was just a coincidence that all my parameters up until then had been integers (record IDs). It turns out that varNull is just an enumerated constant with a value of 1 so I was getting acceptable results (no records) was working okay.
I only need a list of the fields. Maybe I should just parse the SELECT clause of the SQL statement. I thought setting Qry.Prepared to True would get me a list of the fields but no such luck. It wants values for the parameters.
If you have an idea, I would sure like to hear it. Thanks for any help.
Replied again 'coz I'm interested. My methods works (with my queries) because they have been pre-defined with the params' datatypes preset to the correct type:)
I'm not sure how you are expecting the query to know or derive the datatype of the param given that you are not even selecting the field that it operates against.
So I think your query setup and user input method will need more attention. I've just looked up how I did this a while ago. I do not use a parameterised query - I just get the "parameter values" from the user and put them directly into the SQL. So your sql would then read:
SELECT s.hEmployee, e.sLastName
FROM PR_Paystub s
INNER JOIN PR_Employee e ON e.hKey = s.hEmployee
WHERE s.dtPaydate > '01/01/2008'
therefore no parameter type knowledge is necessary. Does not stop your users entering garbage but that goes back to input control :)
Although a slightly different dataset type this is what I use with TClientDataset simple and effective :)
for i := 0 to FilterDataSet.Params.Count -1 do
begin
Case FilterDataSet.Params.Items[i].Datatype of
ftString:
ftSmallint, ftInteger, ftWord:
ftFloat, ftCurrency, ftBCD:
ftDate:
ftTime:
ftDateTime:
.
.
.
end;
end;
can you not do something similar with the query?
You guys are making this way too hard:
for i := 0 to Qry.Params.Count - 1 do begin
Qry.Params[i].Clear;
Qry.Params[i].Bound := True;
end;
I'm not sure what version of Delphi you are using. In the Delphi 2006 help under Variant Types, it says:
Special conversion rules apply to the
Borland.Delphi.System.TDateTime type
declared in the System unit. When a
Borland.Delphi.System.TDateTime is
converted to any other type, it
treated as a normal Double. When an
integer, real, or Boolean is converted
to a Borland.Delphi.System.TDateTime,
it is first converted to a Double,
then read as a date-time value. When a
string is converted to a
Borland.Delphi.System.TDateTime, it is
interpreted as a date-time value using
the regional settings. When an
Unassigned value is converted to
Borland.Delphi.System.TDateTime, it is
treated like the real or integer value
0. Converting a Null value to Borland.Delphi.System.TDateTime raises
an exception.
The last sentence seems important to me. I would read that as varNull cannot be converted to a TDateTime to put into the field, and hence you get the exception that you're experiencing.
It also implies that this is the only special case.
Couldn't you do something like:
for i := 0 to Qry.Params.Count - 1 do
begin
if VarType(Qry.Params[i].value) and varTypeMask = varDate then
begin
Qry.Params[i].value := Now; //or whatever you choose as your default
end
else
begin
Qry.Params[i].value := varNull;
end;
end;
What I ended up doing was this:
sNull := 'NULL';
Qry.SQL.Add(sSQL);
for i := 0 to Qry.Params.Count - 1 do begin
sParamName := Qry.Params[i].Name;
sSQL := SearchAndReplace (sSQL, ':' + sParamName, sNull, DELIMITERS);
end;
I had to write SearchAndReplace but that was easy. Delimiters are just the characters that signal the end of a word.
TmpQuery.ParamByName('MyDateTimeParam').DataType := ftDate;
TmpQuery.ParamByName('MyDateTimeParam').Clear;
TmpQuery.ParamByName('MyDateTimeParam').Bound := True;

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