Visual C++ :: Const Member Functions
Jan 24, 2013
Code:
class Editor {
// c'tors etc
Gtk::EventBox canvas_event_box;
void functionA();
void functionB() const;
[Code] ....
When I try to compile functionB in Visual C++ it gives me this error:-
glibmm/refptr.h(199) : error C2440: 'initializing' : cannot convert from 'const Gdk::Window *' to 'Gdk::Window *'
Conversion loses qualifiers
And this is the code from glibmm/refptr.h
Code:
// The templated ctor allows copy construction from any object that's castable. Thus, it does downcasts:
// base_ref = derived_ref
template <class T_CppObject>
template <class T_CastFrom>
[Code] .....
I don't actually want to change anything in the member variable canvas_event_box. I just want to be able to call one of its functions from my 'const' member function. Is there any syntax I can use to tell VC++ that I'm not actually changing the variable - just using it.
View 11 Replies
ADVERTISEMENT
May 13, 2013
What is the programmers responsibility with respect to const char * returned by various functions, like the C++ string class c_str() function which returns a const char * to an c style string array? In VC++ I cannot delete a const char * which holds a string literal. Take the following code for example:
Code:
void func() //a useless function with illustrative code {
string s1("abcd");
string s2("efgh");
const char * cc1 = s1.c_str(); //c_str() returns a const char * c style string pointer
s2.c_str(); //this returns a const char *, which must be allocated on the heap right?
delete cc1; //produces run time error in Release mode in VC++
}
The problem with the above code snip is that space is allocated on the heap (or so I believe) for the const char *'s returned by the 2 calls to c_str(). The delete attempt fails and there is no opportunity to delete the space allocated by const char * because its not assigned to anything (however I see c_str() used this way extensively)
So, if I cannot delete a const char *, how does the memory get recovered? Perhaps the string objects s1 and s2 themselves have pointers to the items on the heap made by c_str() calls and they get deleted by the destructors of s1 and s2 when the function ends?
View 3 Replies
View Related
Apr 11, 2014
What I need to know is how I can pass an argument to the Book constructor so I can change the const data member Category (with cascading capacity if possible. I also posted some of my set functions for further comprehension.
class Book
{
friend void CompPrice(Book &,Book&); //friend function that has access to the member functions of this class
//The arguments sent to it are by address, and of type the class Book, so that it can have access to its member functions
private: //private data members
[Code].....
View 2 Replies
View Related
Sep 27, 2014
i am trying to describe the unusual situation where you declare a class member function with this format:
bool class::function_name(void) const
Specifically where the 'const' follows the parameter list. It is my understanding this is a very useful way of ensuring that whatever code you put in the function definition cannot change any data members of its class.
However I have recently read that this form of declaration should not be used as it leads to less optimized and slower code. Is this correct?
View 3 Replies
View Related
Apr 18, 2013
class Tracker {
public:
static const int type;
typedef cv_types::CvType<type>::type_t type_t;
};
const int Tracker::type = 1;
gives me the error:
'I' : invalid template argument for 'cv_types::CvType', expected compile-time constant expression
Shouldn't the static const int be a compile time constant?
How would I specify it, so that it works?
PS.: The code works with #define type 1 at the top of the file and without the static const int.
View 3 Replies
View Related
Jan 23, 2015
I have a class that defines a window (a popup dialog of sorts), and I want the name of that window to be constant. The only problem is that the name of the popup needs to match the title of the parent window, and I get the name of the parent in the constructor. So how do I go about defining this member variable to be constant and initializing it with a value in the constructor?
I want to do something like this, but I know this isn't allowed:
/* class.h */
class foo {
public:
foo(*parentWindowPtr);
[Code] .....
I should mention that yes the name of the parent window is const char *, and I would like to keep it this way.
View 4 Replies
View Related
May 27, 2014
i want to store reference to a const object in my class as a member variable, as follow:
I basically want a readonly reference to |Data| in Device object.
Code:
class Device {
Device(const QList<QSharedPointer<Data>> & dataList) : _listRef(dataList) {
} protected:
const QList<QSharedPointer<Data>> & _listRef;
}
This does not allow me to initialize _listRef as something like NULL when it is not applicable.Also, i must change all my constructors and its child class to include an initialization of _listRef!!
What is the alternative? Is pointer the nearest? which of the following should be used?
Code:
const QList<QSharedPointer<Data>> * _listRef;
or
const QList<QSharedPointer<Data>> *const _listRef;
or
const QSharedPointer<QList<QSharedPointer<Data>>> _listRef; ????
View 7 Replies
View Related
Oct 17, 2014
My code is here [URL]
void Player::Display() const
{
cout << "
Player Name: " << GetName() <<
"
Grade: " << GetGrade() << "
G.P.A. " << GetGPA() << endl;
}
The problem occurs in here, I get access violations, is there a way to this while keeping Display const or is this code valid and my problem is somewhere else and not being caught in the debugger? I tried to make the return types const - but that didn't work .....
//Getters need const twice for this to work?
const char* Player::GetName() const {return m_name;}
const int Player::GetGrade() const {return m_grade;}
const double Player::GetGPA() const {return m_gpa;}
[Code].....
View 2 Replies
View Related
Sep 27, 2013
If you are doing some big program, usually, how do you organize the files? Put the class and its member in head file, but where to declare non member functions and where to define them? I don't want to put them all in one cpp file. If not, how to make them visible to the main cpp file?
View 4 Replies
View Related
Aug 31, 2014
So I have a class object that contains the private member variable spot and the public member function MoveLock. Within MoveLock, is a member variable called numbers that holds the place where a user is on a "lock knob". Now, what I'm trying to accomplish is that whenever the user turns the "knob" in the wrong direction, the position is updated with that current numbers so that the clicks needed to unlock the first state is also updated. But I get these errors:
Error E2096 C:Users...switchtest.cpp 34: Illegal structure operation in function main()
Error E2294 C:Users...switchtest.cpp 39: Structure required on left side of . or .* in function main()
Ultimately, what I have in main() is a piece of what I'm going to implement in a class member function. I'm also thinking about moving the if else statements out of the for and creating a second one for the else portion.
#include <iostream>
#include <windows.h>
#include <iomanip>
using namespace std;
HANDLE inKeys = GetStdHandle(STD_INPUT_HANDLE);
HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE);
[code]....
View 10 Replies
View Related
Mar 5, 2014
Assume a class named Dollars exists. Write the headers for member functions that overload the prefix and postfix ++ operators for that class.
View 1 Replies
View Related
Oct 5, 2013
Are there other ways of calling a const/non-const override? I want to defined some functions in terms of others, particularly accessors which might or might not require constness- in order to not copy & paste code. This is my current solution:
struct dumbArray {
dumbArray(unsigned int size):
m_array(new int[size]){
}
~dumbArray(){
delete m_array;
[Code] .....
View 10 Replies
View Related
Dec 7, 2013
difference between const and static const, more effectively. I know the basic concept of const and static but I need clear explanation of declaring "const" and "static const"
Ex:
const int a;
static const int a;
View 5 Replies
View Related
Jun 19, 2013
Is there any way to cast a non-const variable to const one?
I want to read variable n from file and then use it to declare array "int arr[n]", but because n is non-const, the compiler doesn't allow me to do that.
View 6 Replies
View Related
Jan 3, 2014
#include "stdafx.h"
#include <iostream>
#include <math.h>
using namespace std;
class Calc {
[Code] ....
when i built it, it showed the following errors:
1>------ Build started: Project: rough, Configuration: Debug Win32 ------
1> rough.cpp
1>e:c programs
ough
ough
ough.cpp(17): error C3872: '0xa0': this character is not allowed in an identifier
1>e:c programs
[Code] ....
Need sorting out the errors!!!
View 3 Replies
View Related
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?
View 5 Replies
View Related
Feb 28, 2014
Suppose I make a class, something like having the constructor being invoked first makes sense, I don't have a problem with that. But, how could I limit access to functions until certain functions are called? Perhaps this isn't built into the language so you can't. And maybe this problem never comes up. For example if you have a set() and get() functions, if they are both public functions, there doesn't seem to be a way for the compiler at least now if set() never gets called you shouldn't call get(). I just see this as error prone if you need to use libraries, you have to know not to do it from documentation instead of something the compiler can check.
View 11 Replies
View Related
Mar 30, 2013
how to access the private and protected member functions of the class.....
View 5 Replies
View Related
Nov 1, 2014
I was able to get this program running. Now I working on taking one of my member functions and turning it into a standalone function. I choose the create_board() function. Yet, if I declare it in my header file or my main.cpp it cant access any info from the original member functions?
main.cpp
#include "ticTacToe.h"
#include <iostream>
#include <limits>
[Code]....
View 2 Replies
View Related
Sep 27, 2014
This week we are learning to use templates, and I don't understand how to call my member functions with my template based class. I tried the standard convention of calling member functions, but I keep getting an error saying name following"::" must be a class or namespace name. I'm thinking my problem lies with my typename T, but I am unsure. Line 16 is where I am getting tripped up.
#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
template<class T>
T Set
{
public:
[Code]...
View 2 Replies
View Related
Sep 30, 2013
I am a newbie to C++ and VS ++. I have created a windows form application by dragging and dropping button, label..etc. i wish label text to be appeared as return value from a function. The function returns ' const char* '.how this returned string pointer can be used to display label text.?
View 9 Replies
View Related
Oct 17, 2012
I have a basic vector/point class where I've overloaded a bunch of arithmetical operators:
Code:
#pragma once
class point {
public:
point() {
}
point(float p_x, float p_y, float p_z) : x(p_x), y(p_y), z(p_z)
[Code] ...
I can use it fine like
Code:
point p(50,50,50);
point q(50,50,50);
point t = p * q + q;
However when I put this point type into a struct and try to access the members after passing it through by const reference:
Code:
struct sextic {
point a,b,c,d,e,f,g;
};
inline static sextic sexticDifference(const sextic &p_sextic1, c
[Code] ....
This gives me an "operator not defined" error for compilation.
View 2 Replies
View Related
Aug 17, 2013
I am supposed to implement the member functions of class Person.
class Person {
public:
Person();
Person(string pname, int page);
void get_name() const;
void get_age() const;
[Code] ....
The code I wrote is below. Where I am struggling is the program does not allow me to input age. Therefore, I cannot test if my temp for age works. It automatically defaults to 0 because it hasn't taken input. Here is my code:
// Program Title: Person function
// Program Description: The program prompts the user for first and last name and age.
// It then prints the output that was provided by the user.
#include<iostream>
#include<string>
using namespace std;
class Person {
[Code] .....
View 13 Replies
View Related
Dec 16, 2012
In my MFC, CMyPorpertyPageDlg is derived from CPropertyPage. How to access its member function from a nonmember function in the same CPP file?.
void Non_Member_Get_PorpertyPage()
{
CMyPorpertyPageDlg* pPageDlg = ....
}
View 4 Replies
View Related
Jul 13, 2013
So I start thinking about what's the difference between this 2 code
map<const int, float> map_data;
map<int, float> map_data;
But it seems I can't find the difference, is there any difference between this 2 code ?
View 1 Replies
View Related
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?
View 7 Replies
View Related
