NaCl's questions

I am working on a small modular system where the users who work in the company can also be consumers or end users of the application, but in this case, those employees stop working in that company, but they are not deprived of using the software, they only lose those administration accesses.

The administration records are not deleted until after a year, so the records stay there in case the employee returns, so the deletion should only happen once a year.

Each user who registers in the application has a record in the table Profilesand the field HasAdminRightsset to zero / false, but if this same user starts working in the company (remote case, not impossible) , then an entry is created in the table AdminRightsand set HasAdminRightsto 1/ trueto access the system administrative tools.

These are the possible meanings of the values ​​of both fields:

• In a normal case, HasAdminRightsit should be 1 and Revokedit should be 0.
• If an employee stops working in the company, HasAdminRightsit becomes 0 and Revokedis 1.

This is the schema I have from the database:

--
-- Customer profile table.
--
create table Profiles (
  [ID]                  int 
  identity(1,1)         primary key  not null,

  -- ... Algunos campos ...

  [DisabledAdminRights] bit          not null default 1,
  [RegisterDate]        datetime     not null,
  [LastLoginDate]       datetime     not null
);

--
-- Administrator rights.
--
create table AdminRights (
  [ID] int 
  identity(1,1)       primary key not null,
  [ProfileID]         int         not null unique,
  -- ... Otros campos ...
  [AccessGrant]       datetime    not null,
  [Revoked]           bit         not null default 0,
  constraint fkProfID4EmpRights foreign key ([ProfileID]) references Profiles(ID)
  on update cascade on delete cascade -- No idea whether this is good or not.
);

In short, what I need to know is how to change the value of the field [Revoked]in the table AdminRightswhen the table field DisabledAdminRightsis Profileschanged to 1or true?

I have tried a Stored Procedure:

create procedure SetRevoked
  @ProfID
as
begin
  update AdminRights set Revoked=1 where ProfileID = @ProfID
end

But I don't know how to make it run every time the user makes that change in his profile.

I have read the C11 standard and it contains an interesting feature of the C language and that is the use of _Generic...

Due to its context, I imagine that it is used to make generic expressions in the language, but I don't quite understand it.

This is the code I've tried:

#include <stdio.h>

#define ObtenerTipo(x)                   \
          _Generic((x),                  \
   char      : "char",                   \
   short     : "short",                  \
   int       : "int",                    \
   long      : "long",                   \
   long long : "long long",              \
   default   : "desconocido"             \
)

int main(void) {
  return printf("Tipo: %s\n", ObtenerTipo(0xDEADBEEF0);
}

What it throws on my computer is:

long

How does it work _Genericin C language?

I have read somewhere a question that was about the pointer to voidor void *and the doubt about the reserved word voidof several languages ​​has arisen.

I have this code:

typedef enum VALUE_TYPE {
  VT_INTEGER, VT_STRING, VT_BOOL, VT_NULL
} valuetype_t;

typedef struct VALUE {
  void *iv;
  valuetype_t tp;
} value_t;

But I don't understand much what the void *in the is for struct.

As far as I understand, in c and c++ , the type voidis everything and it is nothing, but I am not very clear about what this is about.

Can someone explain to me what it is voidand its functions in the various languages ​​that use it?

_{Note: I've only used c and c++ because I'm not sure about using the language-agnostic tag , feel free to edit this snippet and the question tags.}

I've seen a related one here , but it's not the same answer.

Just as the title says, many of us know that the difference (both in features and syntax) between standards is quite large, ANSI C (C89, C90) did not allow many things that C99 onwards allows, such as the definition of a type in its declaration or the definition of a variable in a loop... Even one-line comments!

The question arises when having to make code that works under all C standards:

• ANSI C (C89 & C90)
• C94
• C99
• C11

Because I can't use the type long longand some 8 and 16 bit platforms don't allow certain values ​​causing integer overflow , likewise the compiler on these platforms is from when K&R (1972+) , others are from 1990, for what I don't have the new functionalities.

I have the following problem, assuming my project structure is the following ( /is the root).

/bin                   # Directorio vacío, es la salida del makefile.
/include/*.h           # assembler.h core.h utils.h, Todos los headers estan aquí.
/src/assembler/*.c     # assembler.c tokenizer.c y otras herramientas del ensamblador.
/src/core/*.c          # utils.c core.c y todos los ficheros del núcleo compartido.
/src/machine/*.c       # bla.c foo.c .... Todos los ficheros de la máquina virtual.

All projects under /srchave the project as a dependency core, but have access to the directory headers/include

Using GNU makeI need to be able to compile only one of the projects I am working on, without the need to alter other projects, so far I have used the following Makefile:

# #$@% Makefile
CC=gcc
FLAGS=-Wall -Wextra -Wpedantic -Werror -std=c11 -O3
INCLUDES=-Iinclude

checkbin:
    # Ensure bin is there.
    @if [ ! -e "bin" ]; then mkdir "bin"; fi

assembler: checkbin # First check for binaries folder.
    $(CC) -o bin/assembler $(INCLUDES) $(FLAGS) src/core/*.c src/assembler/*.c

vm: checkbin
    $(CC) -o bin/vm $(INCLUDES) $(FLAGS) src/core/*.c src/machine/*.c

clean:
    @if [ -e "bin" ]; then \
        rm -rf "bin"; \
    fi

default: assembler # set assembler to default...

He Makefileactually does the work, but he does a lot of work; it is recompiling the coreevery time i go to compile some other project like machineor assembler.

To compile them separately I know I have to use the flag -c, gccbut when inputting multiple files with this flag, it doesn't allow me to use the flag -oto specify the output, for example:

$(CC) -c $(FLAGS) $(INCLUDES) /src/core/*.c 
# Si intento poner -o "bin/core" en este caso, me arroja error

How can I move the compiled files of the dependency project , for this case, coreinto their respective directory /bin/coreso that it can be used later to compile any other project?

For example:

/bin/core/utils.o
/bin/core/core.o

And binds to the following statement:

# Asumiendo los valores puestos arriba:
assembler: checkbin
    @if [ ! -e "bin/assembler" ]; then mkdir "bin/assembler"; fi
    # ... <- instrucción que pondrá los .o en el directorio /bin/assembler/*.o
    $(CC) -o /bin/assembler/assembler /bin/core/*.o /bin/assembler/*.o
    # Sólo necesitamos enlazar los archivos objeto.

I'm developing an application that requires to put/free and re-allocate memory in a somewhat excessive way, but I have a doubt regarding the use of the function realloc(void *, size_t), I have the following code:

void Resize(void *ptr, size_t sz) {
    if (ptr == NULL || sz == 0) 
        return;                   /* No se ve afectado. */

    void *tmp = realloc(ptr, sz); /* Aquí sucede mi problema. */

    if (tmp == NULL) 
        return;                   /* No pasa nada en caso de NULL */

    /* Otra logica... */
} 

On the line: void *tmp = realloc(ptr, sz);my question is the following:

If after this line I release the memory ptras follows:

free(ptr);

Will the pointer tmpstill be valid and point to the new ^ memory address given by realloc?

^: I say new because I don't know if it reallocworks mallocto give memory addresses by resizing them.

Good,

I'm learning to work with pointers in C and I have a question about an algorithm I'm implementing that makes extensive use of malloc, reallocand free, this is the code:

List.h

#ifndef _LIST_H_
#define _LIST_H_

typedef struct {
    int    Count;
    void **Elements;
} List;

List *list_new();
void  list_insert(List *l, void *elem);
void *list_getelem(List *l, int offset);
void  list_removeoffset(List *l, int elem);
void  list_free(List *l);
int   list_get_count(List *l);

#endif

List.c

#include <stdio.h>
#include <stdlib.h>
#include "List.h"

List *list_new() {
    List *ptr = malloc(sizeof(List));
    ptr->Elements = malloc(sizeof(void*));
    ptr->Count = 0;
    return (ptr) ? ptr : NULL;
}
void list_insert(List *l, void *elem) {
    if (l->Count == 0) 
        l->Elements = realloc(l->Elements, sizeof(void*));
    else 
        l->Elements = realloc(l->Elements, (sizeof(void*) * l->Count));
    l->Elements[l->Count] = elem;
    l->Count++;
}
void *list_getelem(List *l, int offset) {
    if (offset < 0 || offset >= l->Count) return NULL;
    return l->Elements[offset];
}
void list_removeoffset(List *l, int elem) {
    if (elem < 0 || elem >= l->Count) return;
    l->Elements[elem] = NULL; 
    l->Count--; 
    l->Elements = realloc(l->Elements, sizeof(void*) * l->Count);   
}
void list_free(List *l) {
    if (l) {
        free(l->Elements); free(l);
    }
}
int list_get_count(List *l) {
    return l->Count;
}

My problem arises within the method declaration list_removeoffset(...)I can't remove an element at a position offsetin the pointer array.

main():

List *MyList = list_new();

list_insert(MyList, (int*)3416); printf("List Count Now: %d\n", list_get_count(MyList));
list_insert(MyList, (char*)"hello world"); printf("List Count Now: %d\n", list_get_count(MyList));
list_insert(MyList, (int*)5); printf("List Count Now: %d\n", list_get_count(MyList));

This is the result I get with the above code:

List Count Now: 1
List Count Now: 2
List Count Now: 3
Element at position 1: hello world

It sure works, but when trying the following code to remove the elements:

list_removeoffset(MyList, 1); // Intento remover el elemento en la posicion 1.

Apparently it is deleted, but, in the same way, it frees the memory of the other elements that are after this one and shows me the result 0.

How can I remove or release just one item and not all the ones after it?

Hi, I have the following query:

select 
    Seg.NombreUsuario, count(RelA.IDSeguidor) as `Siguiendo`, count(RelB.IDASeguir) as `Seguidores` 
from Perfiles as Seg 
    inner join Relaciones as RelA on RelA.IDSeguidor = Seg.ID 
    inner join Relaciones as RelB on RelB.IDASeguir = Seg.ID
where Seg.ID = 1
    Group by Seg.NombreUsuario
    Order by Seg.ID

For the following scheme:

create table Perfiles
(
    ID int primary key AUTO_INCREMENT,
    NombreUsuario varchar(25) not null,
    Clave varchar(25) not null,
    Biografia varchar(300) null,
    Edad int not null default 0,
    Seguidores int not null
);

create table Relaciones
(
    ID int primary key auto_increment,
    IDSeguidor int not null, 
    IDASeguir  int not null, 
    constraint fkIDSeg foreign key (IDSeguidor) references Perfiles(ID) 
    on update cascade on delete cascade, 
    constraint fkIDAs foreign key (IDASeguir) references Perfiles(ID) 
    on update cascade on delete cascade
);

When I run the query on a table that has the following values ​​(I've left the query so you can check with the same test data):

insert into 
    Perfiles(NombreUsuario, Clave, Biografia, Edad, Seguidores) 
values 
    ('root',      '123456',     'Una biografia 1',        18, 0), 
    ('prueba2',   'valor',      'Otra bio',               16, 0), 
    ('controles', 'contrase;a', 'Biografiaaaaa',          24, 0),
    ('cabello',   'perez34',    'Juanjoseguillermopere"', 30, 0),
    ('mrpelo',    'cebolla20',  'Mr Pelo1',               20, 0),
    ('cabeza1',   'lolololo',   'lololo cabezaaa',        13, 0),
    ('otrouser',  'user10',     'prueba 300',             17, 0),
    ('prueba3',   '123543',     'Prueba 3',               14, 0),
    ('xJeremy',   '13-SISN',    '-6-004 :))',             19, 0),
    ('elultimo',  'elultimo',   'el ultimo',              16, 0);

insert into
    Relaciones(IDSeguidor, IDAseguir)
Values
-- ID 1, sigue al ID 6 y asi...
    (1,6), (3,4), (1,8), (4,1), (5,1), (6,1),
    (5,2), (2,5), (8,1), (1,8), (6,1), (6,3),
    (2,6), (1,9), (9,1), (4,8), (3,7), (7,1),
    (7,3), (5,6), (5,7), (5,8), (8,5), (1,5),
    (9,8), (8,9), (10,1), (1,10), (10,2), (10,3),
    (10,4), (4,10), (8,10), (7,10), (3,10), (10,5),
    (5,10);

It gives me the following results:

+---------------+-----------+------------+
| NombreUsuario | Siguiendo | Seguidores |
+---------------+-----------+------------+
| root          | 48        | 48         |
+---------------+-----------+------------+

However, if I run the following query:

Select 
    Seg.NombreUsuario, Count(Rel.IDASeguir) as `Siguiendo`
from Relaciones as Rel
    inner join Perfiles as Seg on Rel.IDASeguir = Seg.ID
where Seg.ID = 1

It returns the correct amount to me in the field Siguiendo (6) .

What I can be doing wrong?

I saw Equiso 's comment in one of my answers with an interesting detail, and that is that he implemented an interface (or part of it) without using the operator :to the right of the object name.

Provided the following code:

public class TestEnumerator
{
    private int _veces;
    public TestEnumerator(int veces) { _veces = veces; }
    public object Current  { get { return "Hola " + _veces; } }
    public bool MoveNext() { return _veces-- > 0; }
}

public class Test
{
    public TestEnumerator GetEnumerator() { return new TestEnumerator(10); }
}

public static void Main()
{
    var test = new Test();

    foreach (var x in test)
        Console.WriteLine(x);
}

Indeed the output is as expected:

Hola 9
Hola 8
Hola 7
Hola 6
Hola 5
Hola 4
Hola 3
Hola 2
Hola 1
Hola 0

Which is equivalent to implementing an IEnumerable<T>e IEnumeratorin their respective classes. What is this type of implementation called? Since it's a class with an enumerator, but it's not a collection, I'd say it's a half-baked implementation of IEnumerable.

As the title says, is there a way to get the internal data type of a variable in Python 3?

In C# I can compare it as follows:

var str = "Strings";

if (str.GetType() == typeof(string))
    Debug.WriteLine("str es un string.");

But I can't find a way to do it in python.

I have the following problem.

I have a List<string>with information that can vary depending on the actions taken and I need to remove all the elements that match the string.

I have tried the following code in the List<T>:

List<string> Strings = new List<string>() {
    "658", "123", "321", "123"
};
foreach (string s in Strings) Console.WriteLine(s); // Imprime: 658, 123, 321, 123
Strings.Remove("123");
foreach (string s in Strings) Console.WriteLine(s); // Imprime: 658, 321, 123

And I need the last loop to foreachreturn 658, 321.

I know I can loop through the List, but I need to understand why not all matching elements are removed.

Greetings.

Hello, messing around with C# and C++ I have found that the following type of expressions is valid:

int A, B, C, D, E;
A = B = C = D = E = 1;

Based on this action, I'm assigning 1 to E, Eto , Dand so on, until I get to the end.

My main question is the following, why is this type of expression valid?

According to the IL ( Generated by DotNetFiddle ) when performing this action I get this:

.method public hidebysig static void  Main() cil managed
{
// 
    .maxstack  2
    .locals init (int32 V_0,
                  int32 V_1,
                  int32 V_2,
                  int32 V_3,
                  int32 V_4)
    IL_0000:  nop
    IL_0001:  ldc.i4.1
    IL_0002:  dup
    IL_0003:  stloc.s    V_4
    IL_0005:  dup
    IL_0006:  stloc.3
    IL_0007:  dup
    IL_0008:  stloc.2
    IL_0009:  dup
    IL_000a:  stloc.1
    IL_000b:  stloc.0
    IL_000c:  ret
} // end of method Program::Main

And the IL generated by the following assignment:

A = 0; B = 0; C = 0; D = 0; E = 0;

It is the following:

.method public hidebysig static void  Main() cil managed
{
// 
    .maxstack  1
    .locals init (int32 V_0,
                  int32 V_1,
                  int32 V_2,
                  int32 V_3,
                  int32 V_4)
    IL_0000:  nop
    IL_0001:  ldc.i4.0
    IL_0002:  stloc.0
    IL_0003:  ldc.i4.0
    IL_0004:  stloc.1
    IL_0005:  ldc.i4.0
    IL_0006:  stloc.2
    IL_0007:  ldc.i4.0
    IL_0008:  stloc.3
    IL_0009:  ldc.i4.0
    IL_000a:  stloc.s    V_4
    IL_000c:  ret
} 

I don't understand much about IL but according to the code above, the method that assigns one variable to another takes up more space in memory and so on, or something similar (Please correct me if I'm wrong) .

My question is, do both codes really do the same thing?

Hi, I have the following example:

public class Material
{
    public class Compuesto
    {
        public const int Peso = 33; // El peso del compuesto siempre es el mismo.
    }
    public int GetPesoCompuesto()
    {
        return Compuesto.Peso;
    }
}

And the code Main():

public static void Main()
{
    Material Mat = new Material();
    Console.WriteLine("Peso del compuesto: " + Mat.GetPesoCompuesto()); // Funciona, retorna: 33
    Console.WriteLine("Peso del compuesto: " + Mat.Compuesto.Peso); // Error.
    Console.WriteLine("Peso general: " + Material.Compuesto.Peso); // Tambien funciona.
}

My question is, Why can I access the constant Pesowithout instantiating the class in any variables, i.e. shouldn't the constant only be defined when I instantiate its class?

I am learning to use C++ templates from stland this library contains a class list<T>, I understand that it has functions similar to those of vector<T> (If not, please illustrate me) .

My question is, how can I access an element within an object of type list<T>at a given index?

So far I have tried this:

std::list<int> Numeros = /* Mi asignación aquí */;
int n = Numeros[0]; // Error.

However, using it std::vector<T>works perfectly:

std::vector<T> Numeros = /* Alguna asignación */;
int n = Numeros[0]; // Asumiendo que tenemos un elemento aquí, me devuelve el valor.

Is it possible to access the values ​​contained within a list<T>using an index?

I am working with the scanner of an interpreter that I am making, but I find that the class StreamReaderbecomes a bit slow with somewhat heavy files, so far I have the following:

using System.Collections.Generic;
using System.IO;
abstract class Scanner
{
    // Campos...
    private char[] Input;

    public virtual IList<Token> Scan()
    {
        // Código para escanear.
        return Tokens;
    }

    public Scanner(string _path, bool _debug)
    {
        // ...
        using (StreamReader sr = new StreamReader(_path))
            Input = sr.ReadToEnd().ToCharArray(); // Lee todo el archivo y lo convierte a un char[].
    }
}

My problem is the following, is there a way to not have to read the entire file and convert it into an array charto use throughout the scan? What I am looking for is to read the file, return the next character and close the file without keeping it in memory and remembering the position of the last character read.

I was looking at one of the questions and I had the doubt that the title says.

Why is the keyword allowed finalinside methods and functions?

I am "optimizing" the code of some interpreter that I am doing and for this I need to know the size in bytes of my class Token, which is made up of two variables: Type (enum), Value (object)and an override of the method ToString():

enum TokenType { String, Keyword, Ident, Number, Symbol }

class Token
{
    TokenType Type;
    object Value;
    public override string ToString() { return "Type: " + Type.ToString() + "\t\tValue: " + Value.ToString(); }
}

When I use a class for definition, it doesn't allow me to do sizeofin said class, however, when I define Tokenas a struct:

struct Token
{
    TokenType Type;
    object Value;
    public override string ToString() { return "Type: " + Type.ToString() + "\t\tValue: " + Value.ToString(); }
}

The sizeofdefault function doesn't let me know the size, so I managed structto get it to give me the result:

Console.WriteLine(Marshal.SizeOf(typeof(Token))); // Resultado: 16

I have read some answers from SO but I still have the same question about this function, why can't sizeofde System.Runtime.InteropServicesor the original function be used in a class, but in a struct?

Tinkering with C# I've found that you can create a new instance without storing it inside some identifier.

I understand that these declarations only work with classes because of the need to call some method within them, but does this instance always remain in memory?

Example, suppose I have the following class:

class Printer
{
    private string _internal;
    public void Print() { Console.WriteLine(_internal); }
    public Printer(string s) { _internal = s; }
}

And I call from:

static void Main()
{
    new Printer("Hola Mundo!").Print(); // Imprime "Hola Mundo"
}

Will the object of type Printerthat was instantiated always remain in memory until the end of the execution of the program?

Good! I have 3 classes, one is TokenBase, which is used as parent of the other classes:

abstract class TokenBase
{
    public TokenTypes Type { get; set; }
    public virtual object Value { get; set; }
    public override string ToString()
    {
        return $"Type: {Type}\t\t Value: {Value}";
    }
}

Derived classes:

class StringToken : TokenBase
{
    private string _Value;
    public new string Value 
    {
        get { return _Value; }
        set { _Value = value;}
    }
    public StringToken(string v) { Type = TokenTypes.String; Value = v; }
}

class SymbolToken : TokenBase
{
    private string _Value;
    public new Symbols Value 
    {
        get { return _Value; }
        set { _Value = value;}
    }
    public SymbolToken(Symbols v) { Type = TokenTypes.Symbol; Value = v; }
}

The problem lies when I want to call ToString()o Valueon one of the derived classes inside the list:

public static void Main(string[] args)
{
    IList<TokenBase> Tokens = new List<TokenBase>();
    Tokens.Add(new StringToken("Hola Mundo"));
    foreach (TokenBase T in Tokens)
    {
        Console.WriteLine(T.ToString()); 
        // Obtengo la siguiente salida: "Type: String         Value: "
        Console.WriteLine(T.Value.ToString()); // Obtengo: ""
    }
    Console.ReadLine();
}

// Salida esperada: "Type: String         Value: Hola Mundo"

How can I directly access the property Valueof one of the derived types?

Good! I have the following code:

public class Persona
{
    // ...
    public string Apellido;
}

public class Program 
{
    public static void Main()
    {
        Persona A = new Persona(); A.Apellido = "Mendez";
        Persona B = A; // El apellido debe ser Mendez.
        //Pero...
        Console.WriteLine("Apellido de A: " + A.Apellido); // Mendez ahora.
        A.Apellido = "Castillo"; // Si por algún "error" debo cambiarlo.
        Console.WriteLine("Nuevo Apellido de A: " + A.Apellido); // Castillo ahora.
        Console.WriteLine("Apellido de B: " + B.Apellido); // Castillo igual.
    }
}

Why is the field Apellidoin variable B affected by the change in variable A and vice versa?