C++ :: Map Container - Calling Overloaded Virtual Method
Oct 7, 2013
Im trying to create a map container with the key being an ID number and the value being a pointer to a class object. Currently Im creating objects and storing their address in the container. I am getting a runtime error when calling the virtual method with this pointer. I believe that the problem is being called because they aren't being called pointer/reference. let me know if you need more.
I've got the following code with output. I can't figure out myself why it's what printed out there. I believe, it has something to deal with overloading/overriding/virtual functions implementations in C++:
class Base{ public: virtual void f(int); virtual void f(double); }
[Code].....
Thus here're my conclusions: 1) in line d.f(1.0); for some reason compiler preferred casting double->int of the argument and then call to 'Derived::f(int)'.
2)in line pb->f(1.0); for some reason compiler preferred call to 'Base::f(double);'. 'Base' is static type of pb, but the dynamic type is 'Derived'.
I believe the answer has to deal with the fact whether virtual table contains in addition to functions' names also the types of arguments they accept. AFAIK, vTable doesn't include such info.
I believe I have the syntax correct but I'm having difficulty calling my overloaded == operator in main (last snip-it of code). Below are several files explaining the code.
Commission.h here is where the friend bool operator == exists and I believe I have it initialized correctly.
#ifndef COMMISSION_H_INCLUDED #define COMMISSION_H_INCLUDED using namespace std; class Commission {
#include <iostream> using namespace std; struct A { virtual void f() { cout<<"A "; } };
[code]...
I would expect that both examples 2 & 3 will give me the same result.I tried to figure it out but I could not. Both are references of a base class type, that get a derived object.
Q1 : why is the difference between them ?
As I see it, its kind of a mix between pointer - which in case of virtual method that was override in derived class - would give me the derived method (e.g. "B") and between regular object - which in case of virtual method that was override - would give me the specific method (Still "B"). So, example 2 "use" it as a regular object and example 3, "use" it as pointer.
Q2 : How should I refer to it ? I am using VS2008.
A quick clarification on virtual methods after reading Jumping int C++ by Alex Allain. If a user wanted to extend a class from someone elses library and override its methods that do not contain virtual methods; how would one call the overridden class if it is referred to by its super type
in other words how would someone override a method from someone elses library that does not have virtual keywords.
Allow users to enter their name and favorite saying in a single method that gets invoked two times. If I can only return one value at a time, how am I suppose to get name and favorite saying out of UserInput()?
I'm still working on my process API, as in my previous posts. Right now I'm trying get my class portable so I can use it for any language/compiler by using a factory design pattern. I'm having problems figuring out how to call the methods properly from my interface pointer in my factory class without causing a segmentation fault.
Code: main.cpp Code: #include "exports.h" #include <iostream> using namespace std;
I would like to avoid throwing things in constructors as much as possible.
Is this good design to have a static class method that checks arguments the caller will give to the constructor. The documentation of the class will say, thou shall call this method to validate thine arguments before calling the constructor, or else segfault may befall thoust.
class Base{ public: int getNum(); private: int numToGet; } class Derived: public Base { public: friend ostream& operator<<(ostream& output, const Derived &B);
I have a program which when a button is clicked on Form1 it runs a vision system operation on an image in a window on a Form1. There are also other buttons on the Form1 which can change things like threshold levels so the inspection can be run again with different settings. It all works fine but I want to change it to remove the buttons from Form1 so that when the user clicks on a button on Form1 it opens up another form, Form2, and all the buttons which were on Form1 are now on Form2 and the image analysis should run on Form1 when the buttons are used on Form2. I have taken over all the code from Form1 to Form2 and I'm trying to make this happen by creating a new oject on Form1 which calls a method on Form2 which contains the code which was in Form1 and called when the button was clicked on Form1 - not working!! I have a constructor in Form2 but I think I have become monumentally confused.
This was the code which was on Form1 when the inspection button was clicked.
I've been trying for more than one month to access a method found in a library called libcocosnas_static.a. I'm using Cocos2d-X version 2.0.4. The library has been used many times by my company to make games using cocos2d-1.0.1-x-0.12.0 without any problem.
This is what I've done: 1- I added the include paths of the library to both eclipse and Android.mk 2- Included the .h file using #include "NASPlatformUtil.h" 3- Added the libcocosnas_static.a file to the proj.androidobjlocalarmeabi folder 4- Added "LOCAL_WHOLE_STATIC_LIBRARIES += cocosnas_static" to the Android.mk file 5- Called the function using: NASPlatformUtil:: openUrl("http://xxx.xxx.com/");
I can right click on the function, click Open Declaration and get it without any problem, but the compiler keeps on giving me that dreaded error...
I have a question similar to the one here: [URL] .....
The main difference is I would like to pass a method of derived class as a parameter to some other method in its template base class.
template <typename BaseType> class Base { public: typedef void (Base::*Callback)(int A);
[Code] .....
The above is an example which does not compile. My compiler complains that the two BaseMethod() calls in DerivedMethod() are invalid uses of non-static member function.
Is this not possible to do, or is my syntax simply wrong? All I want is to be able to pass as an an argument to a method in the base class from the derived class some callback as a variable for the base class to invoke later.
I am currently having trouble to have getline to read line from the file. Error is: "no instance of overloaded function "getline" matches the argument list"
code is as follows:
std::ifstream config("config.txt"); string process[4]; int linecount = 1; if (config.is_open) { while (config.peek() !=EOF) { getline(config, process); linecount++; } }
What I'm trying to do is create a class for constructing an 'op tree' for parsing infix notation.
I started with a base class that uses a map of lambdas to actually calculate the operations (since they are mostly 1 line functions) of passed in integer or float values.
This base class just uses a templated T type as the lvalue and rvalue. I realized though that if I overload the math operators, +, -, etc.. I could also use the class itself as a type for the lvalue and rvalue. This lead me to think I could easily create the op tree by using Operation class members themselves as operands, which I think makes sense but I'm having some trouble expressing the code.
Example, if you look at the main() function I create normal operations easily with integer values. I then try to create a "tree" operation that includes 2 sub-operations as it's rvalue and lvalue, that is where I'm having some conceptual problems as far as implementing the code to do that.
why can't << operator be overloaded as a member function is it because that is the way c++ is written and you just can't or is there another reason because I'm confused.
I'm having an issue with output, luckily everything else works!! I'm working with Mixed Numbers and operations on them. So, here's the code I'm testing with:
I keep getting this error in my code. I believe it is because to use pow(x,y) both x and y have to be double, but how do i put that into my formula under calculations?
#include <iostream> #include <cmath> #include <iomanip> #include <string> #include <fstream> using namespace std; int main() { // Declaration section: Declaring all variables.
I have two possible questions; can you use a ternary operator to initialize objects with overloaded constructors like
class thing { int x; int y;
[Code].....
I can get around it if I need to but I'd like to learn more about the ternary operator if I can, since I couldn't find anything online that addressed this particular issue, at least in a way I could detect.
I have 2 header files one contains my personType class which works independently as I created it for a previous lab and a binarySearchTree<Type> which allows you to create and do various functions with binary search tree's like inserting, searching,and deleting. Which also works independently usings numbers and strings. But when I have combined the 2 trying to make a binary tree of type personType I am running into this problem I can't seem to figure how to fix. The entirety of my code is provided for these 2 header files.
Error1error C2678: binary '==' : no operator found which takes a left-hand operand of type 'std::istream' (or there is no acceptable conversion)
