C++ :: Calling Defined Function Pointer From Another Pointer To Class Object?
Aug 19, 2014
I am attempting to implement function pointers and I am having a bit of a problem.
See the code example below; what I want to be able to do is call a function pointer from another pointer.
I'll admit that I may not be explaining this 100% correct but I am trying to implement the code inside the main function below.
class MainObject;
class SecondaryObject;
class SecondaryObject {
public:
[Code]....
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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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Nov 6, 2013
Right now I have code
#include <iostream>
using namespace std;
class Rectangle {
private:
double width;
double length;
[Code] .....
it gives error ...
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Mar 14, 2013
I'm trying to call a function via a function pointer, and this function pointer is inside a structure. The structure is being referenced via a structure pointer.
Code:
position = hash->(*funcHash)(idNmbr);
The function will return an int, which is what position is a type of. When I compile this code,
I get the error: error: expected identifier before ( token.
Is my syntax wrong? I'm not sure what would be throwing this error.
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Aug 12, 2013
I know what are pointer's and how to use them but there is one point i am not able to understand. Below is the example code
I understand everything in the below code except 1 thing why i am using pointer to base class object in vector int the main() Function?
Code:
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
// base class
[Code] ...
Here is the lines of code i want to understand.
Code:
vector<Employee*> employees;
employees.push_back(&emp1);
employees.push_back(&mgr1);
I know if i will not use the pointer base class function "virtual double grossPay" will be called for both base class object and derived class object and when i will use pointer with reference to the object because base class function is virtual it will look for same function in derived class and if available it will execute it.
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Dec 4, 2013
I have this code:
#include "stdafx.h"
#include <iostream>
using namespace std;
void square_cube(float *x,float *y) {
[Code] .....
The function should pass the square of the first input parameter and the cube of the second input parameter back to the calling routine. I thought I could use a recursion but its not going to work.
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Aug 4, 2013
#include <iostream>
#include <vector>
#include <string>
#include <map>
using namespace std;
struct bop {
string realname; //real name
[Code] ....
Okay, so first thing's first. The program will not compile due to lines 39-45. If I were to change those pointers into regular objects, it will not change the values of my class object. So what is the right way to do this?
I want the user to be able to input the # of employers/programmers into the system. But I cannot do that with an array of classes because when declaring an array; the array size must be constant.
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Mar 20, 2013
Lets say we have a class that holds a pointer member to another object. If I delete that pointer in the destructor I get an error (and I understand why). My question is : is it possible to overcome that without memory leaks ?
1 #include<iostream>
2 using namespace std;
3
4 class A {
5 public:
6 ~A() {
7 cout<< "~A()" <<endl;
[Code] ....
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Feb 14, 2013
lets say I have a pointer p_unit of type c_unit* (c_unit is an a.b.c.)
I have a function that returns a pointer to a new c_unit object:
c_unit * man_add_unit() {
c_unit * local_p_unit;
unsigned short int local_run_code;
print_man_add_menu();
local_run_code = get_a_run_code(); // this bit just gets user input
switch (local_run_code)
[code]....
I assign that to p_unit, then add it to a vector v_units:
p_unit = man_add_unit();
v_units.push_back(p_unit);
cout << "New unit added.
";
The whole program runs on a loop, and another thing the user can do is to print out data on c_unit objects pointed to by v_units. The problem is, in that function up there ^ I give the user the option to go back to main menu without creating a unit.
Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.
I tried to make an if thing with p_unit == 0 but this always returns false and doesn't catch the "bad" unit that will subsequently cause a crash.
Btw, I have considered assigning a reference to a generic c_unit object to that there local_p_unit so it won't return null, then remove pointers to that object from v_units at the end of the loop.. But I know there's got to be a better way.
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Jan 14, 2015
Is there a way to copy a derived class object thru a pointer to base?
For example:
class Base { public: Base( int x ) : x( x ) {}
private: int x; };
class Derived1 : public Base { public: Derived( int z, float f ) : Base( z ), f( f ) {}
private: float f;};
class Derived2 : public Base { public: Derived( int z, string f ) : Base( z ), f( f ) {}
[Code] ....
The question is whether *B[0] would be a Derived1 object and *B[1] a Derived2 object?If not, how could I copy a derived class thru a pointer to the base class?
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Jul 24, 2013
class A (abstract)
class B : A
class C {
void add ( A(&*?) a )
std::vector<std::unique_ptr<A>> data; //unique_ptr<A> because A is abstract and therefore vector<A> isn't possible
}
upper situation. What is the best way to pass add an object of class B to C?
with C::add(A* a){ vector.push_back( unique_ptr<A>(a) ); }
and
int main() {
C c;
c.add( new B() );
}
This works, but i don't think it's very nice, because you could delete the pointer in main. What happens then with the unique_ptr? I could probably make C::add( std::unique_ptr<A> u_p ); but maybe it can be avoided that the "user" (in main() ) has to create the unique_ptr itself.
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Apr 12, 2013
i need to pass myboard.board (board is in the class Cboard and it is an array of int) to a function in a class called piece however this is troubling . i need to pass it as pointer os that i could change its value here under is my code.
main.cpp Code: #include<iostream>
#include"board.h"
#include "pieces.h"
[Code].....
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May 30, 2013
I'm making a code that uses a Function pointer. The problem is, when I try to compile appears an error like:
error: no matching function for call to 'rnVector::rnVector()'
Here's part of the code:
phiFunction::phiFunction(double (*f)(rnVector), rnVector (*df)(rnVector)) {
//... Here comes the code stuff...
}
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May 20, 2014
I have a Qt classes as follow:
Code:
class Vehicle {
public:
void AddData(QString str, Data* data) {
_myDataMap.insert(str,data);
} virtual void Init();
[code].....
My questions are:
After the main function called d1->Modify; the data stored in _myDataMap will get modified too.
What is the more appropriate way of passing the Data through AddData in such case?
If i do AddData(const Data & data), i will not be able to use inheritance of Data, i.e passing a subclass of Data to AddData.
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Feb 6, 2015
I create an instance of a base class (not derived class) and assign it to base class pointer. Then, I convert it to a pointer to a derived class and call methods on it.
why does it work, if there is a virtual table?
when will it fail?
// TestCastWin.cpp : Defines the entry point for the console application.//
#include "stdafx.h"
#include <iostream>
class B
{
public:
B(double x, double y) : x_(x), y_(y) {}
double x() const { return x_; }
[Code] ....
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Jul 29, 2014
I have found that when I dump a C++ object from memory to a file - it seems that there is a misplacement of the last Virtual-Function-Table pointer - in that appears at the beginning. The result is that the gdump information based on this object dump (using green hills) is incorrect. I copied the contents of the gdump information below. The executable is compiled in linux.
Basically MEIO::CameraStatus contains an item that relates to its parent class (line 188). Then it has 18 items that are all Diagnostics::EventsCounter items. Now for each Diagnostics::EventsCounter item there is a Virtual-Function-Table Info Pointer as its last item. All is fine and good except that the last item of MEIO::CameraStatus which is _selfReset is missing its last item of 4 bytes (which is the Virtual-Function-Table Info Pointer ). On the other hand - right before the first Diagnostics::EventsCounter item ("_vidErrors") - there is an extra 4 bytes which happens to be the Virtual-Function-Table Info Pointer. As I said the gdump information file does not see this.
Why the object memory "moves" the last Virtual-Function-Table Info Pointer to the beginning (right before _vidErrors) and is there a way to "fix" this?
///////////////////////////////////////////////////////////////////////////
"MEIO::CameraStatus" val:0x000002f0 ind208,-1) Struct-Begin Info
188: "" offset 0, Parent-Class Private Info C++ Struct ref = 114
189: "_vidErrors" offset 160, Member Info C++ Struct ref = 128
190: "_vdiErrors" offset 480, Member Info C++ Struct ref = 128
[Code] .....
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Feb 19, 2013
Is there a way to call a function whose name is defined in a file-stored-list?
In other words: The caller doesn't know in compile time the name of the function.
I'm not talking about polymorphism.
The problem is: I have a list of function names stored in a file, that may change every now and then, and I'd like to call them in the sequence they appear in that list.
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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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Nov 30, 2013
I have a class Calendar which has an attribute of priority queue, that accepts records of structure defined as:
typedef void (Calendar::*eventPointer)();
struct activationRecord {
double Time;
int Priority;
eventPointer activationEvent;
};
And here is the problem. Whole day I've been trying to fill the Calendar with some test entries by calling the method
void Calendar::calendarPush(double Time, int Priority, eventPointer event)
This is how I call it
calendar.calendarPush(Time, Priority, &Calendar::calendarEmpty);
But Visual Studio keeps to warn me with this error
argument of type "bool (Calendar::*)()" is incompatible with parameter of type "eventPointer *"
#include <iostream>
#include "Calendar.h"
using namespace std;
int main() {
cout << "Initializing ..." << endl;
double Time = 0.0;
int Priority = 0;
[Code] ....
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Mar 9, 2013
I need understanding this block of code, particularly this line : *getLeftChild() { return this - _child; }
Code:
public class UpperNode {
BOX _box;
int _child;
FORCEINLINE UpperNode *getLeftChild() { return this - _child; }
...
};
Here I have this function:
Code:
void
UpperNode::visulization(int level) {
if (isLeaf())
_box.visulization();
else
if ((level > 0)) {
[Code] .....
It also makes calls for "getLeftChild()";
But I see that getLeftChild expects function pointer, and I absolutely have no clue where "this" comes from inside function body.
(return this - _child) - "this" has to be integer.
Or, if we gave pointer, and "this" is referring to some UpperNode, then I can't understand to which one, I have no UpperNode array defined or something. So if this functions is actually scaling pointer address, then scaling where to? I could comprehend it, if I had some array of UpperNodes, but not just class. I have UpperNodes array defined in other friendly class, but don't think they are related .....
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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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Mar 16, 2013
Let's look at this simplified code, it gives compilation error
#include <iostream>
using namespace std;
class A {
public:
void showInfo() { cout << " This is an instance of A" << endl; }
[Code] ....
Without using pointer, how to make this works?
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Aug 15, 2012
I have in the past written code for templated functions where one function argument can be either a function pointer or a Functor. Works pretty straightforward.
Now I am in a situation where I am actually trying to pass a function pointer as template argument to a class. Unfortunately this does not work, I can pass the Functor class but not the function pointer. Below code illustrates the issue:
Code:
#include <string>
#include <iostream>
#include <sstream>
#include <cstdlib>
// For demonstration
const char * external_library_call() {
return "FFFF";
[Code] .....
The idea is to have the definition of the Record class simple and readable and have a maintainable way to add auto-conversion functions to the class. So the lines I commented out are the desirable way how I want my code to look. Unfortunately I could not come up with any way that was close to readable for solving this.
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Jul 24, 2013
im tasked with creating a linear search script using functions on a 10 element array. the elements are to be supplied by the user as is the search target.
I understand how to create the array and gather that information from the user as well as howto set a variable for "target", this is what im calling it. Those two parts are simple enough.
I am not fully understanding the calling of an array in a function as a pointer. i semi understand the use of a pointer and howto call a normal pointer in a function. i also understand that an array is nothing more then a "special" pointer with a set of consecutive address blocks for the size of the array.
My first user defined function is simple enough
Code:
ReadArray(int A[], int size){
int i;
printf("Please enter %d integer numbers separated by spaces:
", size);
for (i = 0; i < size; i++)
scanf("%d", &A[i]);
}
Sso nothing out of the ordinary there. that should be a standard for loop and use of scanf, sadly prof has not covered ssanf or any of the other options so i am stuck using scanf for now. maybe someday down the line in a other program or after this course ill get the chance to learn about better options for gathering data from the user.
I am confused as to my next function:
Code:
void SearchArray(int A[], int target, int size);
I've not written any code here yet as im not sure if i should call the A[], or *A for the first type of the function?
If i call *A do i then use something like this for my search:
Code:
for (*A = 0; *A < size; *A++)
if (*A < target) or use A[] insteadA?
Code:
for (i = 0; i < size; i++)
if (A[i] = target)
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May 10, 2014
class abc {
public:
int i;
abc * foooo;
};
How do you call * foooo? Say I create:
abc a;
* foooo would have some values for int i.
To get int i of *foooo, I tried a.foooo.i, which doesn't work. How do you call it?
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Feb 2, 2013
There are, or course, better ways to do this, but I need to stick to some rules:
(1) Use only pointer variables and not arrays or structs.
(2) Use the three functions shown--regardless of easier methods.
The program should ask for some input, operate on those numbers, and then display the results. I know I am confused over these things:
(1) All that syntax using '*' and '&' or neither.
(2) How to use the char type correctly.
(3) How to use a char type input as an operator (a + b).
(4) How to use the pointer of the operator variable (+,-,*,/) in an actual equation.
Code:
#include <stdio.h>
#include <stdlib.h>
// *** Prototype Functions ***
void Post_Results (float*);
void Calculate (float*, float*, char*, float*);
void Get_Numbers (float*, char*, float*);
[Code]......
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