C++ :: Function Pointer To Non-static Class Member
Aug 19, 2014
I have the following problem: I am using NLOpt for optimization. The API provides functions to set the objective. This is done as follows:
double objective(const vector<double> &x, vector<double> &grad, void *data)
{
return x[1]*x[0];
}
int main(){
nlopt::opt opti(nlopt::LD_MMA,2);
opti.set_min_objective(objective,NULL);
vector<double> x(2);
[Code]....
Now I want to make the function objective a member of a class:
class Foo {
public:
double objective(...){..}
};
How can I give this method to opti.optimize? If I make objective static I can use
opti.optimize(Foo::objective,NULL);
but I do not want to have a static member. Is it possible to create an object of type Foo and give it to opti.optimize?
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Jan 6, 2013
I'm currently programming a server which uses multiple threads- I have a class for one map in the game. Each map has a thread for timed events(tile regeneration, NPC regeneration, etc.), and a thread for handling NPCs(movement, combat, etc.). A basic structure of the class looks like this:
class Region {
public:
/* game values are here, they are public so
they can be accessed from outside of the class
inside of packet-handling functions and such */
int value;
void *Function();
[Code] ....
The program crashes when I use a member of the same class the function is located in- in the context I have shown about it would crash on "value++".
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Oct 7, 2014
How to initialize a static member of a class with template, which type is related to a nested class?
This code works (without nested class):
#include<iostream>
using namespace std;
struct B{
B(){cout<<"here"<<endl;}
};
template<typename Z>
[Code] ,....
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Apr 17, 2013
"You cannot initialize the static data member in the class definition — that’s simply a blueprint for an object and initializing values for members are not allowed. You don’t want to initialize it in a constructor, because you want to increment it every time the constructor is called so the count of the number of objects created is accumulated."
Why don't you want to initialize it in a constructor?
Edit: Because every time it is called it will set it back to 0 or whatever the initializing value.
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Jul 11, 2012
For example, in a header file A.h, I define an abstract class,
Code:
// A.h
class A {
public:
virtual void foo() = 0;
private:
static int _x;
};
How'd I initialize static member data _x?Normally, we initialize a static member data in a cpp file. However, there is not cpp file for A.h. If I intialize _x in header file, there will be linker errors like mulitple defined symbols. What is appropriate way to do that?
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Nov 21, 2014
I have a class having static member.I have get and set methods which will Get and Set Values to this variable. In a multithreaded application does it have any thread safety issues.
Class a {
static int b;
void Set (int c);
int Get();
};
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Sep 9, 2013
Basically I want to create a base class which defines a static data member so that its automatically redeclared as the same static data member in the derived class.
class A{
protected:
static derivable int val;
// A::val
}
class B : public A{
// static derivable int val is already here
// A::val AND B::val
}
This seems impossible to me but I'm wondering if perhaps there's a way to add modifiers to the compiler to do this (or preferably something MUCH simpler)...
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Dec 4, 2014
I am writing my program on C++ language. I have one promblem. I need to set signal handler for my process. As the signal is related with the process on system level I have faced the problem.
My program consists several classes. They are connected together. But it doesn't metter in this case. The problem is that I need to access to member and methods of the class from my signal handler. For instance , I have class named Foo at it has some members and methods.
So from my handler I need to call its function and change members.
I understand that compiler should know that this class instances will exist during all program execution.
I have tried to set static member class Foo instance in another class , but this didn't solve the problem.
What is correct approach to do this. How to correctly implement signal handling in such case.
Here is example of my code
Code:
class MyContainer{
private:
std::vector<Foo> container;
public:
int removeFromContainer(Foo* aFoo) {
[Code] .....
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Aug 27, 2014
I need to keep a static variable in a member function of a class that I have many objects of. I've had some trouble with it, and when I read up I found that such variables are static across all instances. Is there any way around this?
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Mar 8, 2014
What am I doing wrong with static members and methods here?
compiler errors:
1>test.obj : error LNK2005: "private: static int Test::count" (?count@Test@@0HA) already defined in main.obj
1>c:usersjamesdocumentsvisual studio 2013Projectsstatic_testReleasestatic_test.exe : fatal error LNK1169: one or more multiply defined symbols found
test.h
#ifndef TEST_H_
#define TEST_H_
class Test {
[code]....
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Jul 20, 2013
Say you had:
class Foo{
public:
//...
void funky();
[Code] .....
Would each instance of Foo create a new counter variable, or would it remain the same for all of them, i.e. baz.funky() would always use the same counter variable? What if the class was a template?
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Oct 10, 2013
If I need a static pointer to a class that is used globally(multiple files), and I only want to allocate memory once.
One way is to create a function that returns a static pointer of type class and call it where ever you need this pointer. My question is there another way to do this like with a header file and include the header file where you need to use the object of type class.
static class* function
{
static class c;
if (c == NULL)
{
c = new class;
}
return c
}
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Apr 25, 2013
I am doing fixed point implementation in c++ which is done by the following code
#ifndef __fixed_point_header_h__
#define __fixed_point_header_h__
#include <boost/assert.hpp>
#include <boost/static_assert.hpp>
#include <boost/operators.hpp>
#include <limits>
[Code] ....
I am getting the error ambiguous overload for âoperator<â in âbeta < ((-5.0e-1) * pi)â
I know the problem the static member function cannot access the members and objects of structs. am i right?
and how to solve this problem, do i need to implement the cossin_cordic function as a non member function.
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Sep 11, 2013
What are the workarounds for accessing the non-static member variables of some class(Say A) inside static member functions of another class(Say B)? I am coding in c++. Class A is derived with public properties of class B. Any pointers?
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Dec 5, 2014
I'm writing a class "Property" for a program that manages different types of properties. This is my .h for y base class. I was trying to write a virtual void function to convert different children classes to strings that can be displayed, but Xcode is freaking out.
I had it as:
virtual void toString()= 0;
and it gave me an error message: "Virtual can only exist in non-static member functions" and "field has incomplete type 'void'"
I changed it to:
virtual string toString() = 0;
and the error message didn't change.
Is this an issue with Xcode or did I do something wrong? Even after changing it to string it told me that it "has incomplete type 'void'"....
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Feb 10, 2013
I am modifying a set of static variables inside of the class's member function. The static variables are private. An example of what I'm doing is as below,
utilities.h
-----------
class utilities {
private:
static int num_nodes;
public:
void parse_details(char* );
[Code] ....
I get a compilation error in the function void utilities::parse_details(char* filename)
which says: undefined reference to `utilities::num_nodes'
compiler: g++
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Jan 10, 2015
I have the following scenario :
Code:
class test {
public :
int num;
};
int main() {
test t1;
test *ptr = &t1;
int test :: *mem_ptr = &test::num;
}
I need to access mem_ptr (pointer to a class member) through :
a. object (t1)
b. pointer to the object (ptr).
How can i do that ?
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Sep 4, 2012
I am trying to use 'this' pointer but i am confused why 'this' pointer is not available for static member functions.
Code:
#include <iostream>
#include <fstream>
#include <stdlib.h>
using namespace std;
const int MAX = 20;
const int MAXPTR = 100;
class name {
private :
char fname[MAX], mname[MAX], lname[MAX];
[code].....
I am using GNU GCC Compiler via Code::Block
Error : 'this' is unavailable for static member functions
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Jan 30, 2013
Here is the assignment: (3pts) Given the following class header file, write the class’ source code for each of the accessor and mutator functions listed. (How the functions have listed their parameters, varying between passing by reference and by value.) Don’t forget to comment your code – it counts!
class Album {
private:
char * artist; // band or singer’s name
char * title; // title of the album
[code]....
The input will be an array. My questions: First, am I on the right track?
When using (char * a) for a function, for example, this is passing the address of a, correct? so then *artist=a; changes what the address of a points to?
also, the functions are bool when I would expect void. Why? for all of the set_" " functions, the parameter is *... but for set_record_label it is *&. That appears to be a mistake to me. Is that right?
what is the difference between *& and * as parameters?
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Sep 19, 2014
This project is for an embedded micro controller. In the project i wrote a class that generically services uarts. then i declare 6 objects of that class and hand them configurations for each specific uart.
internally all the objects have a send buffer of data that is still to be sent that gets populated by the object member function.
how can i make an array of function pointers that can point to the same member but of six different objects.
for example (not a working one)
class uart {
private:
struct myData {
unsigned char data[20]
int head
int tail
int count;
[Code] ....
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Mar 6, 2013
Below is a working program. Please note that the vector <int*> pointer is declared as a public member of the class A.
The problem arises when I try to make it a private (instead of public). First, let's look at the File 1 below. It compiles and works fine.
File 1: main.cpp (working fine)
#include <vector>
#include <iostream>
using namespace std;
[Code].....
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Sep 18, 2013
How can a member function in my derived class call the same function from its base class?
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Jun 6, 2012
I am trying to use "remove_if" with a predicate function inside a class. The code intends to remove the grid cells which an agent cannot move into (from among all possible cells).
Code:
void classname::function1()
{
vector<MoorePoint> neighbors;
....
[Code]....
That code would work if it was not in a class and the predicate was not a member function. However, now I receive long error messages which I guess refer to incompatibility of remove_if template with the predicate parameter (one error includes : error C2064: term does not evaluate to a function taking 1 arguments).
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May 15, 2013
I have a class with member functions and a pointer like this:
Code:
class MyClass{
private:
typedef void(MyClass::*memFnPtr_t) ();
public:
memFnPtr_t fnptr;
void fn1();
void fn2();
};
Now in a regular function I create an instance of the class and try to assign the pointer:
Code:
MyClass mc;
mc.fnptr = &mc.fn1;
The compiler does not like it and suggests this instead:
Code:
mc.fnptr = &MyClass::fn1;
This seems to work but what if I have two instances of the class:
Code:
MyClass mc1, mc2;
How does the compiler know to distinguish between
Code:
mc1.fn1
and
Code:
mc2.fn1
when the assignment now looks identical:
Code:
mc1.fnptr = &MyClass::fn1;
mc2.fnptr = &MyClass::fn1;
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Nov 26, 2013
I have the following piece of code.
Code:
#include<iostream>
using namespace std;
class Test {
public:
Test(){cout<<"Test"<<endl;}
void fun() {
int i=5;
[Code] ...
Compiled with g++.
Executing this give output fun5.
It is correct? I have not allocated any object and so this pointer is not created. Then how it is able to run and call the function.
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Aug 21, 2013
I am writing a program which is using SDL library. I have two different classes which one of them is Timer Class and the other is EventHandling Class.
I need to use some member functions and variables of Timer in some Eventhandling Class member functions, Although I want to define an object of Timer in int main {} and relate it to its member function that has been used in Eventhandling member function in order that it becomes easier to handle it, I mean that I want to have for example two objects of timer and two objects of Eventhandling class for two different users.
I do not know how to relate an object of a class from int main{} to its member function which is being used in another class member function.
Lets have it as a sample code:
class Timer {
private:
int x;
public:
Timer();
get_X();
start_X();
[Code] ....
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