C++ :: Thread With Lambda Function - Swap 3 Variables
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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Nov 15, 2013
write a swap function to swap 2 elements in the vector?
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Apr 23, 2013
I have the following code. According to this the values of pointers p[0] and p[1] remains unchanged since the swap is made to local variables in swap function.Now my doubt is how can I swap the pointers p[0] and p[1] inside the function swap??
Code:
#include<stdio.h>int main(){char*p[2]={"hello","good morning"};
swap(p[0],p[1]);
printf("%s %s",p[0],p[1]);return0;
}void swap(char*a,char*b){char*t; t=a; a=b; b=t;
}
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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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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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Mar 16, 2014
The idea is to make an array and have it sort the contents inside the array in order from smallest to greatest by using a swap function. I don't know why it needs to be done this way when a sort function makes the most sense, but it is what it is.
For simplicity I want my array to only include three numbers. I was thinking {18,-2,24}. My only problem is that I am not understanding how to translate the swap function in an array. I tried using my previous swap function from another assignment and translate it to work for an array, but it doesn't work and I am completely lost and stuck. What I tried to do was this:
#include <iostream>
#include <cstdlib>
using namespace std;
const int SIZE = 3;
double myList[3] = {18, -2, 24};
void swap(myList[0], myList[1], myList[2]) {
[Code] ....
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Jun 26, 2013
writing a sorting function that has an argument for a vector of ints rather than an array; it should use a selection sort algorithm.Here is what I have:
#include <iostream>
#include <vector>
#include <conio.h>
using namespace std;
void fillVector(vector<int> &aVector);
// PRECONDITION: number declared size of array a.
// POSTCONDITION: number_used is the number of values stored in a
//a[0] through a[number_used-1] have been filled with nonnegative int.
[code].....
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Nov 10, 2013
So I been working on this c++ project and I need to be able to take three seperate strings and send them to function to put them in alphabetical order through a-z and use the swap function to return them in order. I been searching for problems like this but I haven't fame across any. I can copy my code onto here as well as a more detailed description of what I'm needing to do onto here if needed.
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Mar 19, 2013
I searched the web for error: C3867... and the discussions where murky or obscure.
My code excerpt is:
#pragma once
#include <windows.h>
#include <stdlib.h>
#include <process.h>
void PutUpfrmIO(void *);
namespace WordParsor {
[Code] .....
I get the generic message:
error C3867: 'WordParsor::Form1::PutUpfrmIO': function call missing argument list; use '&WordParsor::Form1::PutUpfrmIO' to create a pointer to memberc:userskingc++wordparsorwordparsorForm1.h... and the suggestion fix generate another error.
One person suggested the gcroot<> object wrapper... but I do not know how to modify/declair the function or its argument type.
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Jul 30, 2014
I have a class which I wrote and one of its object is "SerialPort" .NET class. In my MainWindow I created instance of my class called "SerialPortComm", then I send through some functions of mine, commands to the Serial Port, and I receive answers through "DataReceived" event.
But when I trying to use Dispatcher.BeginInvoke to write my data I have received (successfully), nothing shows on the RichTextBox which I'm trying to write to.
What can caused that, and How I can make it works?
SerialPortComm.cs
public partial class SerialPortComm : UserControl {
public SerialPort mySerialPort = new SerialPort();
public void Open_Port(string comNumber, int baudRate) {
mySerialPort.PortName = comNumber;
mySerialPort.BaudRate = baudRate;
[Code] ....
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Nov 24, 2014
How to call a thread by a function pointer?
I get "error C2059: syntax error : '(' " on the indicated line.
Code:
#include <windows.h>#include <iostream>
using namespace std;
DWORD WINAPI Thread() {
cout << "ok" << endl;
return 0;
[Code] ....
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Jan 25, 2014
I'm trying to create a thread to a class function, but it doesnt work for me...
The function : void Server::RecMsg(SOCKET &socket)
the call : std::thread GetMessages(&Server::RecMsg, ClientSocket);
I get the error : "Error1error C2064: term does not evaluate to a function taking 1 arguments"
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Apr 20, 2014
I have a header file with a bunch of functions. I want to create a thread using the <threads> package and am using
void myclass::functionX() {
}
void myclass::function() {
std::thread tr(myclass::functionX);
}
I am getting the error "no instance of std::thread::thread matches the argument list argument types are (void());
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Sep 17, 2013
CODE:
class Secure {
private:
int seconds;
bool isRUNNING;
public:
Secure(int seconds) {
[Code] .....
ERROR:
error C2276: '&' : illegal operation on bound member function expression
I read that due to explicit casting, threads cannot be created within a class. I'm trying to thread a scanning system to relieve stress on my main program/module, rather than having the scanner stunt their performance.
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Oct 26, 2014
Write a function which will take 3 arguments. The function needs to return a new number which is formed by replacing the digit on a given position in the number with a digit which is carried as an argument (the position in the number is counted from right to left, starting with one). Write a main program which will print the newly formed number.
Examples:
A function call of 2376, 3 and 5 should return the number 2576
A function call of 123456, 4 and 9 should return the number 129456
What I succeeded to do so far:
Figure out the logic for swapping the digit and write working code for it (in the main function).
What I failed to do so far:
Write a function which will return the desired result.
What is my problem:
I tried writing a function to do this, but as you see from my calculations, my result is divided in 3 parts. I don't know how to return more variables from a function.
Code:
#include <stdio.h>
int main() {
int inputNumber, swapPosition, swapDigit;
scanf("%d%d%d", &inputNumber, &swapPosition, &swapDigit);
int i, numberPart1 = inputNumber;
for (i = 1; i <= swapPosition; i++)
[Code] ...
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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 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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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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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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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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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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Mar 29, 2014
ok I have a class Player with lots of variables and im gonna call a function to checkXp, if I call it with the whole player object does it use a lot more memory then if I just passed the couple things I need?
ex
checkXP(Player* play) // this is a whole object of player
or
checkXP(play->getXP(), play->getLVL()) // the variables I want.
I just realized I may not be able to modify anything from player in the checkXP() function
question 1: does passing the whole object use more memory
question 2: if I passed as just the variables I need, I wont be able to modify anything of object play?
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Jan 24, 2015
In my program I created three separate return functions. Each function is labeled:
int boxes(int x, int y);
int leftOver(int x, int y);
double avgItemsShipped(int x, int y, int z);
Is it bad programming practice to use 'x' and 'y' in all of my functions? Should I use the this keyword inside the function? We use this often in my Java class and I know it exists in C++, but I haven't actually seen it used (or used it myself yet).
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Nov 12, 2012
This is a c program that is failing to compile. The error occurs in the calcLabs() function. The error called out is (btw, I'm using VS 2010): Error4error C2143: syntax error : missing ';' before 'type'
I don't understand why the compiler is not letting me declare variables in the calcLabs() function!
Code:
#include<stdio.h>
#include<stdlib.h>
void calcPercent(double *);
double calcLabs();
double calcExams();
double calcFinal();
char calcLetter(float);
[code]...
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Mar 26, 2013
The following function uses reference variables as parameters. Rewrite the function so it uses pointers instead of reference variables, and then demonstrate the function in a complete program.
int doSomething(int &x, int &y)
{
int temp =x;
x = y * 10;
y = temp * 10;
return x + y;
}
I understand how to covert the reference variables to pointers, however I am stuck on this error. Either I get the error listed in the title or (with a few changes) the error "invalid conversion from 'int' to 'int*'"
What am I doing incorrectly?
#include <iostream>
using namespace std;
int doSomething(int*, int*);
int main(){
int X, Y, result;
[Code] ....
I have multiplied both x and y by 10 and then added them together!
Here is the result " //I really didn't know how else to use the "doSomething" function in a meaningful way. So... I just stated what the function does.
<< result << ".
";
system("PAUSE");
return 0;
}
int doSomthing(int *x, int *y)
[Code] .....
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