jachguate's questions

I am opening a file (csv) for reading, but during reading I get the following error:

'charmap' codec can't decode byte 0x81 in position 328: character maps to <undefined>
...
  File "C:\Users\juan\source\repos\AsoVerde\AsoVerde\AsoVerde.py", line 10, in <module>
    for dato in rdatos:
  File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python37_64\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 328: character maps to <undefined>
The program 'python.exe' has exited with code -1 (0xffffffff).

Which is produced with the following script:

import csv

filename = r"C:\datos\datos.csv"
adatos = open(filename)

rdatos = csv.reader(adatos)
for dato in rdatos:
    print(dato)

The error jumps on the linefor dato in rdatos

I have a table that has customer invoice header records, called Factura, with information like this:

IdCliente  | Fecha      | NumeroFactura | y otros campos
-------------------------------------------------------
1          | 2021-01-01 |        201345 | ...
2          | 2021-01-01 |        201346 | ...
1          | 2021-01-17 |        203148 | ...
1          | 2021-01-31 |        207941 | ...
2          | 2021-02-11 |        209147 | ...
1          | 2021-02-28 |        211249 | ...

And I want to build a query that summarizes the number of invoices per customer for each month of the year, for 2021, with a structure like this:

IdCliente  | Ene  | Feb  | Mar  | Abr  | May  | Jun  | Jul  | Ago  | Sep  | Oct  | Nov  | Dic  |
------------------------------------------------------------------------------------------------
1          |   3  |   1  |   7  |  12  |   0  |   0  |   0  |   0  |   0  |   0  |   0  |   0  |
2          |   1  |   4  |  11  |  21  |   7  |   0  |   0  |   0  |   0  |   0  |   0  |   0  |
3          |   0  |   0  |  17  |  14  |   9  |   8  |   0  |   0  |   0  |   0  |   0  |   0  |
etc.

If the client's name could be included, even better.

How can I do that query?

I have come across a string constant that is preceded by a letter r, of the following form:

a_expresion = r"\[(.*?)\]"

I haven't seen this before and I wonder

• what does the rpreceding the string mean?
• what varies between 'cadena'and r'cadena'?

I have this routine to change the name of a printer in Windows but when I invoke it, it doesn't change the name, it doesn't show any error ¹ either :

function TInformacionSistema.RenombrarImpresora(ANombreActual, ANombreNuevo : string) : boolean;
var
  LTamanio       : DWORD;
  LImpresoraInfo : PPrinterInfo2;
  LManejador     : THandle;
begin
  Result := false;
  try
    // Obtiene el manejador
    OpenPrinter(PWideChar(ANombreActual), LManejador, nil);
    // Obtiene el tamaño necesario para la estructura LImpresoraInfo structure en LTamanio
    GetPrinter(LManejador, 2, nil, 0, @LTamanio);
    // Asigna memoria
    LImpresoraInfo := AllocMem(LTamanio);
    // Llama GetPrinter de nuevo con el LTamanio
    GetPrinter(LManejador, 2, LImpresoraInfo, LTamanio, @LTamanio);
    // Se cambia el nombre
    LImpresoraInfo.pPrinterName := PWideChar(ANombreNuevo);
    // Se guarda la estructura con el cambio
    SetPrinter(LManejador, 2, LImpresoraInfo, 0);

    FreeMem(LImpresoraInfo);
  except
    exit;
  end;
  Result := true;
end;

I call it this way:

var
  iSys: TINformacionSystema;
begin
  iSys := TInforamcionSistema.Create;
  try
    iSys.RenombrarImpresora('Vieja', 'Nueva');
  finally
    iSys.Free;
  end;
end;

¹ : This is a real question I received, via another channel, and I wanted to share it along with my answer with the community (hopefully with the permission of the asker).

I need to activate the functionality ReportMemoryLeaksOnShutdownto report memory leaks for my application, but I want to do it only in debug mode , how can I do it?

project MiProyecto;
uses FastMM;

begin
  ReportMemoryLeaksOnShutdown := True;
  ....
end;

I want to create a string spanning multiple lines to assign to the property Captionof a TLabelin Delphi:

Label1.Caption = 'Hola' + ?? + 'Mundo';

And visually it remains:

Hola
Mundo

How do I manage to do it in Delphi?

I have two records with the same fields, and one of them has a set of methods. Being, in fact, different, why does SizeOfit return the same value for both?

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TData = record
    Age : Byte;
    Id  : Integer;
  end;

  TData2 = record
    Age : Byte;
    Id  : Integer;
    procedure foo1;
    procedure foo2;
    procedure foo3;
  end;

procedure TData2.foo1;
begin

end;

procedure TData2.foo2;
begin

end;

procedure TData2.foo3;
begin

end;

begin
  try
    Writeln('SizeOf(TData) = '+ IntToStr(SizeOf(TData)));
    Writeln('SizeOf(TData2) = '+ IntToStr(SizeOf(TData2)));
    Readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;

end.

Are there any additional runtime costs for calling overloaded methods?

I'm asking this specifically for Delphi , in case the answer isn't the same for all compiled languages.

I think there should be no additional cost since it should be resolved at compile time, but you can never be sure, can you?

I need to clarify on the subject of type casts in Delphi.

I have written an example with two classes, TClassAand TClassB. TClassBinherits from TClassA. The code is the following:

program TEST;

{$APPTYPE CONSOLE}


uses
  System.SysUtils;

type
  TClassA = class(TObject)
  public
    Member1:Integer;
    constructor Create();
    function ToString():String; override;
  end;

type
  TClassB = class(TClassA)
  public
    Member2:Integer;
    constructor Create();
    function ToString():String; override;
    function MyToString():String;
  end;

{ TClassA }

constructor TClassA.Create;
begin
  Member1 := 0;
end;

function TClassA.ToString: String;
begin
  Result := IntToStr(Member1);
end;

{ TClassB }

constructor TClassB.Create;
begin
  Member1 := 0;
  Member2 := 10;
end;

function TClassB.MyToString: String;
begin
  Result := Format('My Values is: %u AND %u',[Member1,Member2]);
end;

function TClassB.ToString: String;
begin
  Result := IntToStr(Member1) + ' - ' + IntToStr(Member2);
end;


procedure ShowInstances();
var
  a: TClassA;
  b: TClassB;
begin
  a := TClassA.Create;
  b := TClassB(a); // Casting (B and A point to the same Memory Address)
  b.Member1 := 5;
  b.Member2 := 150; // why no error? (1)

  Writeln(Format('ToString: a = %s, a = %s',[a.ToString,b.ToString])); // (2)
  Writeln(Format('Class Name: a=%s, b=%s',[a.ClassName,b.ClassName])); // (3)
  Writeln(Format('Address: a=%p, b=%p',[@a,@b])); // (4)
  Writeln(b.MyToString); // why no error? (5)

  readln;
end;

begin
  try
    ShowInstances;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

The output of the program is:

ToString: a = 5, a = 5
Class Name: a=TClassA, b=TClassA
Address: a=0012FF44, b=0012FF40
My Values is: 5 AND 150

And my doubts are:

1. What is the address of Member2? Is this a possible Access Violation ?
2. Does the method ToStringpoint to the same address?
3. Why aand do bthey have the same class name?
4. Are ay btwo different variables?
5. If bit is of type TClassA, why can I use the method MyToStringon it?

I am working on a project where a test page needs to be printed to a particular printer. The printer test page should be the same as what Windows prints when sent from printer properties -> print test page .

how can i do it with delphi?

How can I send to print a Test Page to a printer using Delphi

How can I get a child form to appear on the windows taskbar in Delphi?

I have seen several applications where when a new window is opened, a new button for that child window is created on the taskbar, without creating a new process. By default, in an application written in Delphi, child forms can be created and displayed, but only one button appears on the Windows taskbar, they are not displayed separately when doing alttab.

how can i change this behaviour?

My current code looks like this:

procedure Form1ButtonClick(Sender: TObject);
begin
  Form2.Show;
end;

I've been thinking about calling CreateWindowEx, but my ideal solution should be simpler than having to call the Windows API directly.

I am trying to find a Delphi function to split an input string into an array or list of strings based on a delimiter. I have found many things on Google, but they all seem to have some problem or limitation and I have not found one that I am happy to work with.

I just have to split a string like : 'palabra:doc,txt,docx'into an array based on ':'.

The result would be: ['palabra', 'doc,txt,docx'].

Does anyone have a function that actually works?

Thank you

Original Q&A: https://stackoverflow.com/q/2625707/255257

I have a table with multiple columns, for example ID, Nombre, Edadand Pais. Of these, I have marked the column Edadas unusedwith the following statement:

alter table Persona set unused column AGE;

Now, I want to use the column Edadagain, how can I do it in Oracle (10g)?

Also, which is better, delete a column , or set it to unused ?

What is the difference between a innerand a outer join?

And what is the function of modifiers?

• left
• right
• full

I must save dates and times in different tables of a typical transactional application where I am going to store various information, such as:

• Dates and times at which each transaction occurs (Invoice, Payment Receipt, etc.)
• Dates and times of future events, such as appointments and scheduled deliveries
• Past dates, such as the date of birth of the employee, or of the employee's children.

I have little experience with MySQL and I'm not sure which data type I should choose in each case.

What is recommended, use a field of type DateTime or type TimeStamp and why?

I am making an application in which I would like to receive the temperature through an Arduino. I think using Sockets is a great way to communicate, but I have no idea how to use Sockets in an Android application made with Delphi.

Is it different from how it is used in Delphi compiled for Windows?

Since in jQuery it is possible to change the visibility of an element, how can I tell if an element is visible or not at runtime?