Visual C++ :: Constructor With Functional / Construction Via Lambda?
Feb 17, 2014
I have a class which upon construction has a part which should be executed when the constructor has finished "enough" to make the call valid.
Take the following simplified class example (the actual problem is much more elaborate):
Code:
#include <functional>
class base {
public:
base(int i, std::function<void()> func) : mi(i)
[code]....
Explicitely creating a derived class allows me to properly implement the lambda to call a member of the class.
I can't seem to figure out how to do this for an explicit instantiation of the base class.
Can this be done ? Or is this a shortcoming of VS2012 or something the standard doesn't handle ?
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Jun 10, 2013
How to make a source code into a functional program that a user can open and use without coming across the source code and building or running it.
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Dec 11, 2014
Why something doesn't work without setting global variables. I want to know how to deliver values for example my boolean value "ende" (means end) from the function in line 99
Code:
bool pruefeGewinn() or in line 116 Code: bool spielfeldVoll() to the main function for using it there for Code: } while (ende != true); in line 164.
How to return it correctly?
Here is the Code of the game TicTacToe.
Code:
#include <stdio.h> // In- and Output
#include <stdlib.h> // Implementation of many functions
#include <stdbool.h> // Allows in C99 True and False as Boolean
#include <time.h> // Allows using Random by time
/*----------------------- Constants -------------------------*/
#define KANTENLAENGE 3
#define STRING 100
[Code] .....
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Sep 26, 2014
I have made the following code to illustrate my problem:
#pragma once
#include <bitset>
#include <iostream>
[Code].....
Now I want to avoid my bitset field being constructed before the ConstructTest constructor is called. So at first I tried wrapping it in a unique_ptr but found out that this would give me some potential problems with const functions.
And then I realized I could just set it to NULL, as I have in the above code. I tried that, got unexpected print outs, until I found out that NULL is just equal to 0 in C++ and that the bitset has a = operator that takes a number, int, long or maybe something else. Either way, this effectively constructs the bitset and sets it to the number 0.
So my efforts so far have been shut down. But then how can I avoid the bitset being constructed in advance, if at all possible?
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Jan 24, 2014
I have an AbstractAgent base class that manages a background thread. The actual work done in the background thread is accomplished through a pure virtual function call.
Here's the problem: because the base class is initialized prior to the derived class, there is a race condition in which the pure virtual call might occur before the derived class is initialized. Likewise, on teardown the derived class might deconstruct before the base class destructor has a chance to stop the thread.
I'd like to know if there are any well-known patterns for dealing with this problem. All I can think of is providing start() and stop() methods which can be called from the most-derived class's constructor/destructor, but that strikes me as inelegant.
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Feb 13, 2013
I'm trying to implement 2d array to simulate linked list for stack and I faced several difficulties doing so.
How do I implement from Top to Bottom ordering? How do I check random index value for validity?
Source-code:
Code:
#include <iostream>
using namespace std;
int myTop, index, nex = -1;
int twoDimentionalArray[25][3], L[25];
[Code].....
And one more thing: how do I get straight 0 from 25 index in the first coulumn?
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Mar 6, 2014
I have this method called "walk" and what it's supposed to do is, walk through a bunch of triangles one step at a time (the're all connected [not to each other, but in a mesh]).
To do so, I need to perform a containment test.
Normally, I guess I'd just write a separate function but what if I wanted to be weird and write my inclusion test as a lambda in my walk method? Literally the only function that needs this code is my walk() procedure and I need to call the test an arbitrary amount of times.
Is this frowned upon? Would this be the jarring type of code I've been warned about? Or should I just say yolo and do what I want?
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Mar 31, 2015
I get the following error:
Cannot convert lambda expression to type system delegate because it's not a delegate type (on invoke).
The Second error is: Client.PrivateChat.txtReceive is inaccessible due to its protection level..
private PrivateChat pChat;
private void client_Received(Client sender, byte[] data) {
this.Invoke(() =>
{
for (int i = 0; i < clientList.Items.Count; i++) {
var client = clientList.Items[i].Tag as Client;
if (client == null || client.Ip != sender.Ip) continue;
[Code] .....
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Feb 4, 2014
I have 22 CButtons and I'm trying to set each one to the corresponding position in a CButton array of size 22 in the constructor.
Code:
*buttons[0] = m_button1;
This code gives me an error in the compiler.
error C2248: 'CObject:perator =' : cannot access private member declared in class 'CObject'
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Jun 15, 2013
PHP Code:
using namespace System;
ref class A {
public:
A(){Console::WriteLine(L"A constructor");}
virtual void func(){foo();}
void foo()
[Code] .....
Supposing that class A is the development code; and so for unit-testing purpose I create a mock for it. But I don't know how to override A's constructor such that it will not get executed in my unit-test code.
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Apr 29, 2013
I know memory leak checking can sometimes have false positives. I turned on memory leak checking by adding
Code:
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
Then calling
Code:
_CrtDumpMemoryLeaks();
in the App's constructor.
I traced the issue back to the constructor for a variable included in the app class. The variable is a class I declare in the project.
Code:
//Class declaration
#define NUM_MT_COLORS 16
struct clrTable {
COLORREF clrCode;
CString clrName;
[Code] ....
I get a memory leak error for every instance where a CString is set. I tried moving this to the MainFrame just to see if there was something with this being in the app, and saw the same memory leak errors.
I didn't include the functions in this class that manipulate this table. I didn't put it in the document because this is a multi-doc application and this table is universal to the program.
Is this an example of a false positive in the memory leak checker, or did I do something wrong?
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Mar 8, 2015
I am making a tic tac toe program in which they are asking me to have a 3x3 2 dimensional array of integers and have the constructor initialize the empty board to all zeros. They also want me to place a 1 or 2 in each empty board space denoting the place where player 1 or player 2 would move The problem I'm having is, my code initializes the board to all zeros for each element of the array, and prints it out just fine, but I can't figure out how to re-initialize the values in the array to show where each player moves on the board... I was thinking about having a default constructor that has each value set to zero, and then use a setGame function that can change the values on the board to one or two depending on where the player moves....but I don't know if that's possible.....
here is my code
Code:
// header file
#include <iostream>
#include <array>
class tictac {
public:
tictac(int);
[code]....
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Oct 28, 2012
What the best way to initialize a constructor in an array of objects?
Usually I declare an array of objects like so:
Code:
Car toyota[100];
Is this the only way I know to initialize a constructor of an array:
Code:
for (int i = 0; i < 100; i++)
{
toyota[i] = Car(x, y);
}
Is this the proper way?
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Feb 1, 2013
I'm trying to expand a template + argument parameter list inside a lambda function like this:
template <typename Class, typename ...Args>
static void create(Args ...args) {
// Perform pre-thread creation work.
std::thread([=]()
[Code] ....
But this does not work:
The compiler error is "error: parameter packs not expanded with ‘...’:|"
However, when I do the following:
template <typename Class, typename ...Args>
static void create(Args ...args) {
// Pre-thread work.
auto tthr = [](Args ...ar) -> void {
[Code] ....
It works just fine. That shows that lambda threads are able to take variadic arguments...
So here is my question; what is the correct capture clause for capturing the variadic object correctly?
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May 13, 2014
I am trying to realize a simple code with thread and lambda function.
My goal is to swap 2 variable . I launch 2 thread,
The first:
Put his value in a shared variable and notify it .
wait until an event on a condition variable occur.
read from shared value .
The second wait until an event on a condition variable occur.
Wake up
read from shared value .
Put his value in a shared variable and notify it.
This is the code
thread t1([&p1]()->void{
m.lock();
nt++;
if(nt==1) {
//first thread
unique_lock<mutex> u1(m); ***
[Code] .....
Why it say error "abort() has been called " on the istr ***
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Jan 15, 2014
How to improve my customSort function. It is to accept a lambda function as parameter which customizes your sort in any special way you want.
#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <functional>
enum personType {teacher, student, baby};
[Code] ....
For example, std::vector<Person> people = {Mark, MrMac, Lola, MsWhite, Cindy, Zainab, Mikey, Fred, Zolal} is to be sorted so that teachers will be placed first, then students, and then babies, but with the exception that people with names starting with Z be placed before anyone else, followed by people with age equal to 8. All this is set up by the ordered list:
person.name.at(0) == 'Z',
person.age == 8,
person.type == teacher,
person.type == student,
person.type == baby
So the output gives
Zolal
Zainab (baby)
Cindy
Ms. White
Mr. Mac
Fred
Mark
Mikey (baby)
Lola (baby)
Teachers are supposed to be placed before students, which in turn placed before babies, but Cindy's age is 8, and so is placed before the teachers, and Zolal and Zainab start with Z, so is placed before her. So far so good, but now I want the further sorting result that all people within their subcategories be sorted in their own way, e.g. Zainab should come before Zolal alphabetically, Ms. White should precede Mr. Mac because she is younger, etc... How do I further generalize my customSort function so it carries out those further criteria as well?
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Dec 5, 2014
i have stuck in a join and i cant figure out where the problem is, i have those tables
public class Themes
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
[Code].....
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May 30, 2013
I've was trying out a function template to automatically get the type of a lambda, but it seems that it won't compile
I've tried two different ways:
1.
template<class HASHER>
auto make_unordered_map(size_t bucketCount, HASHER const && hf)
-> unordered_map<string const, HASHER>&& {
return unordered_map<string const, int, HASHER>(bucketCount, hf);
} auto x = make_unordered_map(1, [](string const& key)->size_t { return key[0]; });
2.
template<class HASHER>
auto make_unordered_map(size_t bucketCount, HASHER const && hf2)
-> unordered_map<string const, int, decltype(hf2)> {
return unordered_map<string const, int, decltype(hf2)>(bucketCount, hf2);
} auto x = make_unordered_map(1, [](string const& key)->size_t { return key[0]; });
The test code are located here:
1. [URL] ....
2. [URL] ....
They are both based on the code that is stated to work in those examples. I.e.:
auto hf = [](string const& key)->size_t { return key[0]; };
unordered_map<string const, int, decltype(hf)> m (1, hf);
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Mar 1, 2014
i am writing this bank accounts program using structures. i haven't implemented the function before that i want to check if the data is being read and printed. When i build and run the program in visual studio it gives me the following error. "No constructor could take the source type, or constructor overload resolution was ambiguous". Now whats wrong in this program?
/* Bank Accounts Program */
#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>//needed to use system() function
using namespace std;
const int MAX_NUM = 50;
struct Name{
[code]....
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May 24, 2013
In this code:
// Ex10_15.cpp Using lambda expressions
#include <algorithm>
#include <iostream>
#include <iomanip>
[code].....
The lambda accepts no arguments, but it accesses increment by value and current by reference, the latter being used to store the next value to be set. This lambda has the side effect that current will be updated when generate is finished. The following lambda expression is similar, but without the side effect:
[=]()mutable->T{T result(current);
current += increment;
return result;}
"
I dont exactly understand what side affect it is talking about. Wouldn't you want generate to update current? I understand how the second code fixes it though, just takes everything in the enclosing scope by value.
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Jul 1, 2014
I am trying to write a function that extracts chunks of numbers from a stream (ie if i had "ui33ui24ui23hjdwejf" it would extract the chunk 33), and its finished, but it wont compile. errors here: [URL] ...... its only one line in an include file, but im stumped. anyways, this is the most updated version of the code: [URL] .....
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Jan 25, 2014
VS 2012 / Windows 7 64 bit
class
class myclass {
public:
myclass(){/*stuff here*/}
myclass(int* p) {MyPointer = p; myclass()}
[Code] ....
it works until the myclass(int* p) calls myclass()
then the MyPointer will become CCCCCCCC (NULL value)!
is there a way to stop the second constructor from resetting the pointer value to null?
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Feb 28, 2012
I am trying to use constructor within constructor in the same class. Is that possible. I have tried something and it shows me a error message:
error: type "mainClass" is not a direct base of "glavna"
This is the program I tried:
Code:
class mainClass {
private:
int x,y;
Code] ......
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Jan 1, 2013
Is this example correct? This example from a book
Constructor of the Base Class
Person::Person(char* n="", char* nat="U.S.A", int s=1)
{
name = n;
nationality = nat;
sex = s;
}
Constructor of the Derived Class (inherited from the base class)
Student(char* n, int s=0, char* i=""):
Person(n, s)
Why the initialized list of the base class constructor doesn't match the initialized list of the derived class constructor? I know this book is a little bit old, I'm not sure if this wrong in VC++ 2010?
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Mar 19, 2015
to initialize this object? Why C++ FAQ says no? Here is my code,
Code:
class A
{
public:
A(int x, char c);
A(int x);
[code] ....
I don't have any trouble to call the constructor A(int x, char c) from another constructor A(int x).
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Mar 11, 2013
is it possible to get object name in the constructor? I would like to initialize an object of circle class without any arguments and put some pretty lines in constructor to get and save as table of chars the name of creating object. Is it possible? I work with MSVS2012.
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