New to delphi and database programming in general but am curious if there is a better way to swap records in a TDataset? I have read through some help and cant find any obvious methods. Currently I have a procedure implemented to move records down the dataset until they hit the Eof marker. However I am getting some odd errors when I get to the last record in my data. All I have is implemented a standard array-style swap routine trying to preserve data and whatnot while juggling active records.
Code So Far
procedure TForm2.btnDownClick(Sender: TObject);
var
sTmp,sTmp2 : string;
iTmp,iTmp2 : integer;
begin
tblMatched.DisableControls;
if ( tblMatched.Eof <> true ) then
begin
// Grab data to swap
tblMatched.GotoBookmark( tblMatched.GetBookmark );
iTmp := tblMatched.Fields[0].AsInteger;
sTmp := tblMatched.Fields[1].AsString;
tblMatched.Next;
iTmp2 := tblMatched.Fields[0].AsInteger;
sTmp2 := tblMatched.Fields[1].AsString;
// Swap data
tblMatched.Prior;
tblMatched.Edit;
tblMatched.Fields[0].Value := iTmp2;
tblMatched.Fields[1].Value := sTmp2;
tblMatched.Next;
tblMatched.Edit;
tblMatched.Fields[0].AsInteger := iTmp;
tblMatched.Fields[1].AsString := sTmp;
end;
tblMatched.EnableControls;
end;
It looks like you're using an in-memory dataset, such as TClientDataset. If you simply put an index on the dataset, it will keep things ordered for you so you don't have to rearrange them manually. Just set up the index based on whatever criteria you want to have it use.
Related
I work with a current software for the simulation of power plant processes. Smaller scripts can be written within the software for automation, these scripts are based on Pascal and own function libraries. Was simply retained after the initial release 20 years ago.
My simple script transfers values from one element to another and has this structure:
var f: integer;
S13Be.MXTSTO.data(1,1) := 22;
S12Be.MXTSTO.data(1,S12Be.NFLOW) := 22;
S11Be.MXTSTO.data(1,1) := S12Be.MXTSTO.data(1,S12Be.NFLOW);
S10Be.MXTSTO.data(1,S10Be.NFLOW) := 22;
S9Be.MXTSTO.data(1,1) := S10Be.MXTSTO.data(1,S10Be.NFLOW);
S8Be.MXTSTO.data(1,S8Be.NFLOW) := 22;
S7Be.MXTSTO.data(1,1) := S8Be.MXTSTO.data(1,S8Be.NFLOW);
S5Be.MXTSTO.data(1,S5Be.NFLOW) := 22;
S4Be.MXTSTO.data(1,1) := S5Be.MXTSTO.data(1,S4Be.NFLOW);
S2Be.MXTSTO.data(1,S2Be.NFLOW) := 22;
S1Be.MXTSTO.data(1,1) := S2Be.MXTSTO.data(1,S4Be.NFLOW);
for f := 1 to S13Be.NFLOW+1 do begin
S13Be.MXTSTO.data(1,f) := S13Be.MXTSTO.data(1,1);
end;
for f := 1 to S12Be.NFLOW+1 do begin
S12Be.MXTSTO.data(1,f) := S12Be.MXTSTO.data(1,1);
end;
for f := 1 to S11Be.NFLOW+1 do begin
S11Be.MXTSTO.data(1,f) := S11Be.MXTSTO.data(1,1);
end;
.
.
.
for f := 1 to S2Be.NFLOW+1 do begin
S2Be.MXTSTO.data(1,f) := S2Be.MXTSTO.data(1,1);
end;
for f := 1 to S1Be.NFLOW+1 do begin
S1Be.MXTSTO.data(1,f) := S1Be.MXTSTO.data(1,1);
end;
I would like to put another loop around the outside so that the elements are automatically selected.
The names of the elements are S1Be, S2Be.... S13Be and S1Ent, S2Ent, S3Ent...S13Ent
.MXSTO.data accesses a matrix in the respective element
(1,f) defines the position in the matrix (currently there are only 1x5 and 1x10 matrices; the value .NFLOW specifies which matrix is involved.)
I would be very grateful for a tip, a book recommendation and of course a code.
With best regards
Felix
Translated with www.DeepL.com/Translator (free version)
Names generally no meaning in a compiled program, it doesn't contain them.
If the identifiers are the same type you might be able to define an array of pointers to them, and then iterate using that array.
This can be handled with an enumerated type. The solution will require a little reorganization of your date, but I think it will be worth it. Like most languages variables are independent of each other. If you want to deal with a list of variables they will need to be in a structure of some sort. An array in your case makes sense. However, associating a numeric index with each variable is a bother and requires pointers or some difficult to maintain parsing system.
Nicklaus Wirth created a mechanism to deal with this sort of problem. It is called an enumerated type. For example:
type
BeName = (S1Be, S2Be, S3Be, S4Be);
var
NFLOW: array[BeName] of integer;
MXTSTOdata: array[BeName,1:5,1:10] of integer;
SnBe: BeName;
begin
… Initialization here, the following is how to change your code.
MXTSTOdata(S2Be,1,NFLOW[S2Be]) := 22;
MXTSTOdata(S1Be,1,1) :=MXTSTOdata(S2Be,1,NFLOW[S4Be]);
… Here is just one for loop:
for f := 1 to NFLOW[S1Be]+1 do
MXTSTOdata[S1Be,1,f] := MXTSTOdata[S1Be,1,1];
… Here is a loop of for loops:
for SnBe := S1Be to S4Be do
for f := 1 to NFLOW[SnBe]+1 do
MXTSTOdata[SnBe,1,f] := MXTSTOdata[SnBe,1,1];
Note how the for loop doesn’t need a start and end index. But that depends on which Pascal you are using. Delphi, FreePascal, and standard Pascal differ. You might have to use the first and last element like I showed. You might have a Low and High function available.
var
NFLOW: array[BeName] of integer;
SnBe: BeName;
for SnBe := Low(BeName) to High(BeName) do
for f := 1 to NFLOW[SnBe]+1 do
MXTSTOdata[SnBe,1,f] := MXTSTOdata[SnBe,1,1];
And I might have the syntax for the array declaration wrong. I’ve seen var NFLOW: array of [BeName] of integer; documented on the web, built I haven’t fired up my pascal compiler to check this fragment. However, the enumeration type would help you a lot. Also, there is a for-in construct in FreePascal
for SnBe in BeName do
for f := 1 to NFLOW[SnBe]+1 do
MXTSTOdata[SnBe,1,f] := MXTSTOdata[SnBe,1,1];
The enumeration type is useful in preventing bothersome minor spelling errors from messing up the program, has nice for loop options, and can change the ordering of the values in the enumeration. Changing the ordering may be needed for handling what order assignments are made in, at the cost of program fragility, as you might imagine.
The pred and succ operators are implemented. If you ever wondered what the need were for pred and succ you have now found out. A while loop:
SnBe := S1Be;
repeat
… something
SnBe := succ(SnBe)
until SnBe = S4Be;
Of course that doesn’t get easily to the last value in the enumeration. You could add guard values, but that adds some confusion and messes up the for-in loop.
SnBe := S1Be;
repeat
SomefunctionF(SnBe);
SnBe := succ(SnBe)
until SnBe = S4Be;
SomefunctionF(S4Be);
Is probably the cleanest way to deal with the problem of running in a repeat loop. The reason for adding these examples is you may have two enumerations running in parallel:
type
ToBeName = (S1Be, S2Be, S3Be, S4Be);
NotToBeName = (Bob, Carol, Ted, Alice);
var
NFLOW: array[BeName] of integer;
MXTSTOdata: array[BeName,1:5,1:10] of integer;
Romeo: NotToBeName;
SnBe: BeName;
begin
SnBe:=S1Be;
Romeo:=Bob;
Repeat
ActionFunction(SnBe,Romeo);
SnBe := succ(SnBe);
Romeo := succ(Romeo)
until SnBe = Alice;
Also, this idea might be helpful for your program:
type
EType = (S1Be, S2Be, S3Be, S4Be, Bob, Carol, Ted, Alice);
var
Romeo: EType;
SnBe: EType;
begin
Romeo:= Bob;
SnBe:=S1Be;
repeat
SomeFn(Romeo,SnBe);
SnBe:=succ(SnBe);
until SnBe>S4Be;
The range check applies to pred and succ. For example, the statement
succ(Alice)
would produce an error because there is no element after Alice in the enumerations above.
Lastly, if you need to do things in reverse order you can do:
for SnBe := S4Be downto S1Be do
I am using Arrays for managing my data in and outputs.
My problem is that I need to i/o from or into textboxes which are continously incremented by 1- So my Array starts at 1 and ends at 31. My textboxes which are variables and cannot be arrays are named like memo67... - memo97.
Is it possible in a way that I use a tmepcounter? So I wanted to use something like memo(a+66) in a for loop. With this I could fill my textboxes with my array[a] 1 to 31.
Greets
As Andreas says, usually arrays are used in such case. But if you like me like the quick copy and past action, you can fill such arrays can be using TComponent features with one single procedure:
Type
TForm1 = class
editsset1 : array of tedit;
end;
type TControlDynArray = Array of TControl;
procedure loadarray (root:tcomponent;var x : TControlDynArray;basename:string;i1,i2:integer);
var l,i : integer;
begin
l:=i2-i1+1;
setlength(x,l);
for i := i1 to i2 do
begin
x[i-i1]:=tcontrol(root.FindComponent(basename+inttostr(i)));
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
// loads edit1..31 into editsset1[0] ... editsset[30]
loadarray(self,TControlDynArray(editsset1),'Edit',1,31);
end;
Disclaimer: the above code is pieced together from working code, but I didn't test the endresult
I have these 10 numbers (one in each line) in a Text File and I need them to be sorted in a chronological order starting with the highest number. I wrote a code which works just fine, but the problem is that the code isn't flexible, because once I add another number to the Text File it won't work since the code is set to sort 10 numbers only...this is due to my array of integers which is supposed to read the values before the sorting process starts, but won't allow me to add a variable to the array's properties so it will be able to read and sort any-size text file...I know there has to be a way of making a program which can sort any-size file of this structure, just please tell me how I could improve my code. (If you think my way isn't too efficient, it's because that's my homework from high school and I need to use these arrays to implement a bubblesort).
program Project2;
{$APPTYPE CONSOLE}
uses
SysUtils;
var
numbers, sortednumbers : TextFile;
count : integer=0;
number : array[1..10] of integer;
I : integer;
Procedure Swap(var X, Y : Integer);
var
Temp : integer;
begin
Temp := X;
X := Y;
Y := Temp;
end;
procedure Assign;
var I : Integer;
begin
reset(numbers);
for I := 1 to count do ReadLn(numbers, number[I]);
end;
procedure BubbleSort;
var I, J : integer;
begin
for I := 2 to count do
begin
for J := count downto I do
if (number[J] > number[J - 1]) then
Swap(number[J - 1], number[J]);
end;
end;
begin
AssignFile(numbers, 'Numbers.txt');
AssignFile(sortednumbers, 'Sorted-Numbers.txt');
Reset(numbers);
While not EoF(numbers) do
begin
ReadLn(numbers);
Inc(count);
end;
Reset(numbers);
ReWrite(sortednumbers);
Assign;
BubbleSort;
For I := 1 to count do writeln(sortednumbers, number[I]);
CloseFile(numbers);
CloseFile(sortednumbers);
end.
Use a dynamic array. This is an array that can change the number of elements it holds.
Instead of declaring:
number : array[1..10] of integer;
instead skip the bounds declaration:
Number : array of integer;
Then, before you start using it, set its length:
SetLength(Number, 10);
Once you are done, free the memory by setting it to have length 0:
SetLength(Number, 0);
Note that:
Indexes of a dynamic array start from 0, not 1. That is, Number[0] is the first element and Number[9] is the tenth. This is quite common in programming but can be confusing if it's not something you've come across before.
There are other 'quality' changes you can make to your code too. As commenter David Heffernan said, stop using global variables. I would also suggest using try/finally for resource allocation and cleanup, and using streams (and another link, wrap this over TFileStream) instead of the old-style file IO you're currently doing. Also, consider your variable names - Number for an array of numbers is odd - why not add the S and call it Numbers, for example?
That might be a bit much all at once, so go slowly in small steps, save and backup often (preferably into source control), and have fun!
And if it had not been a school project:
function Comparer(List: TStringList; index1, index2: integer): integer;
begin
try
Result:= StrToInt(List[index1]) - StrToInt(List[Index2]);
except
raise Exception.Create('Your file does not contain numbers');
end;
end;
function SortNumbers
var
lStringList: TStringlist;
begin
lStringList := TStringlist.create;
try
lStringList.LoadFromFile('Numbers.txt');
lStringList.CustomSort(Comparer);
lStringList.SaveToFile('Sorted-Numbers.txt');
finally
lStringList.Free;
end;
end;
However the Delphi RTL uses Quicksort, not Bubblesort.
Is there any simple univesal way to add 2 arrays into one? In the case below it is not possible simply use C := A + B statement...
I would like to avoid making algorhytm for it everytime .
TPerson = record
Birthday: Tdate;
Name, Surname:string;
end;
Tpeople = array of TPerson;
var A, B, C:Tpeople;
C:=A+B; // it is not possible
thanx
Due to the two string fields in each TPerson record, you can't just use binary "move", since you'll mess the reference counting of string - especially in a multi-threaded environment.
You can do it manually - this is fast and nice:
TPerson = record
Birthday: TDate;
Name, Surname: string;
end;
TPeople = array of TPerson;
var A, B, C: TPeople;
// do C:=A+B
procedure Sum(const A,B: TPeople; var C: TPeople);
begin
var i, nA,nB: integer;
begin
nA := length(A);
nB := length(B);
SetLength(C,nA+nB);
for i := 0 to nA-1 do
C[i] := A[i];
for i := 0 to nB-1 do
C[i+nA] := B[i];
end;
Or you can use our TDynArray wrapper, which has a method for handling such cases:
procedure AddToArray(var A: TPeople; const B: TPeople);
var DA: TDynArray;
begin
DA.Init(TypeInfo(TPeople),A);
DA.AddArray(B); // A := A+B
end;
The AddArray method can add a sub-port of the original array:
/// add elements from a given dynamic array
// - the supplied source DynArray MUST be of the same exact type as the
// current used for this TDynArray
// - you can specify the start index and the number of items to take from
// the source dynamic array (leave as -1 to add till the end)
procedure AddArray(const DynArray; aStartIndex: integer=0; aCount: integer=-1);
Note that with such records, it will use the System._CopyRecord RTL function, which is not so optimized for speed. I've written a faster version - see this blog article or this forum thread.
If you use dynamic arrays in functions/procedures, don't forget to use explicitly const or var parameters (as I coded above), otherwise it will make a temporary copy at each call, therefore it may be slow.
There is nothing built in that allows dynamic arrays to be concatenated.
You may consider using one of the generic container classes found in Generics.Collections, TList.
In your case you would have 3 instances of TList, say A, B and C. Then you could write
A.Clear;
A.AddRange(B);
A.AddRange(C);
I think this is as close as you can get to what you want with what is delivered out of the box.
If you are prepared to do a bit of coding yourself then you could make use of operator overloading to use the exact syntax you requires. Declare a record containing an array of TPerson with private visibility. You then need to implement an Add operator, a Count property and a default Items[] property. This could be made generic too so you only need write it once.
TTurboArray = record<T>
private
FItems: array of T;
//property accessors here
public
class operator Add(a, b: TTurboArray<T>): TTurboArray<T>;
property Count: Integer read GetCount write SetCount;
property Items[Index: Integer]: T read GetItem write SetItem; default;
end;
This idea can be extended into a very powerful data structure as you see fit.
There is a quick-and-dirty way to do this. It is a terrible hack, but it should work and even take care of reference counting:
function ConcatPeople(const A, B: TPeople): TPeople;
var
Temp: TPeople;
ALen, BLen: Integer;
begin
Result := Copy(A);
BLen := Length(B);
if BLen = 0 then
Exit;
ALen := Length(A);
Temp := Copy(B);
SetLength(Result, ALen + BLen);
Move(Temp[0], Result[ALen], BLen * SizeOf(B[0]));
FillChar(Temp[0], BLen * SizeOf(B[0]), 0);
end;
In effect, the data in Temp are "swapped" with the empty records in Result, so the balance is maintained and refcounting will keep on working.
Update
For what it is worth: This is aparently the same technique as used in this accepted SO answer and in, e.g. TList<T>.Insert. I had deleted this answer, but I still think it is valid, so I undeleted it again. It could do with a lock around the Move/FillChar block, so no one accesses the items when they are being "swapped". I'll add that.
Here's how I handled it, though it required a slight (but hopefully immaterial to you) modification to your original code to use TArray:
(tested in XE2)
uses
Generics.Collections;
type
TArrayExt = class(TArray)
class function Concat<T>(const First, Second: array of T): TArray<T>; overload;
end;
class function TArrayExt.Concat<T>(const First, Second: array of T): TArray<T>;
var
i: Integer;
l: Integer;
begin
l := Length(First);
SetLength(Result, l + Length(Second));
for i := Low(First) to High(First) do
Result[i] := First[i];
for i := Low(Second) to High(Second) do
Result[l + i] := Second[i];
end;
type
TPerson = record
Birthday: TDate;
Name, Surname: String;
end;
TPeople = TArray<TPerson>;
var
A, B, C: TPeople;
begin
C := TArrayExt.Concat<TPerson>(A, B);
The main difference here is that I use "TArray" rather than "array of TPerson". This can be used for arrays strings, records, etc. I find the main benefit of doing it this way is that it's truly making a copy rather than a move. And I am using the "normal" Delphi functions instead of things like bulk memory copies, which can give me the willies.
Of course, if you were doing this in a tight loop and needed the performance, this way might not be best for you. But I think this is the best for most other situations, especially in terms of maintenance and readability.
(Unless someone posts a comment about how there's some horrible hidden memory leak here. Hopefully not!)
You code works fine in the newest version of delphi C := A+B;.
But for dynamic arrays in older versions you can use the function concat. Example:
C := Concat(A, B);
I have two Delphi7 programs: a COM automation server (EXE) and the other program which is using the automation server.
I need to pass an array of bytes from one program to the other.
After some searching I've found that using variant arrays is the way to go (correct me please if you know any better methods).
My question is:
How do I create a variant array in one program, and then how do I read its values in the other?
I know about VarArrayCreate and VarArrayLowBound/VarArrayHighBound, but I'm unsure on how to do this properly.
Thanks!
You create it like that:
Declarations first
var
VarArray: Variant;
Value: Variant;
Then the creation:
VarArray := VarArrayCreate([0, Length - 1], varVariant);
or you could also have
VarArray := VarArrayCreate([0, Length - 1], varInteger);
Depends on the type of the data. Then you iterate like this:
i := VarArrayLowBound(VarArray, 1);
HighBound := VarArrayHighBound(VarArray, 1);
while i <= HighBound do
begin
Value := VarArray[i];
... do something ...
Inc(i);
end;
Finally you clear the array when you don't need it anymore. EDIT: (This is optional, see In Delphi 2009 do I need to free variant arrays? )
VarClear(VarArray);
That is all there is to it. For another example look at the official Embracadero Help
EDIT:
The array should be created only once. Then just use it like shown in the above example.
For the other side:
(assuming Value is the Variant parameter and the element type is WideString)
var
Source: PWideStringArray;
if VarIsArray(Value) then begin
Source:= VarArrayLock(Value);
try
for i:= 0 to TVarData(Value).VArray^.Bounds[0].ElementCount - 1 do
DoWhatEverYouWantWith(Source^[i]);
end;
finally
VarArrayUnlock(Value);
end;
end;