In C++ if no user defined constructor is provided for a class the compiler automatically provides a implicit default constructor.
An implicit default constructor is equivalent to a default constructor with no parameters and no body ?
So what is the use of a implicit default constructor provided by the compiler, if it is not going to do anything ?
Implicit default ctor does not initialize the built-in data members, so what is it needed for?
View 5 Replies View RelatedFirst I wrote a Binary-tree class to draw a binary tree on the window. The nodes were small circles. Then I become wanted to change the shape of the nodes from circles to triangles by another class, Binary-tree-derived which is derived from Binary-tree class. I wrote the below code to do the job but I get two errors about constructors. First, code:
/* The binary-tree class, one of the topics that has been said in Programming Principles and Practice using C++ book by Biarne Stroustrup.
This code is written by R Abbasi (s.rabbasi@yahoo.com) */
#include <Simple_window.h>
[Code].....
Errors are:
Error12error C2512: 'Binary_tree' : no appropriate default constructor availablec:userscsdocumentsvisual studio 2012projects est_1 est_1 est_1.cpp91
13IntelliSense: no default constructor exists for class "Binary_tree"c:UsersCSDocumentsVisual Studio 2012Projects est_1 est_1 est_1.cpp91
How do you write a default constructor?I need to use a default constructor that will initialize the data members:
- salesPerson to “Unknown”
- noOfWeek to 13
- amount to point to an array of thirteen 0.00s.
This is my weeklysales class
class WeeklySales {
char* salesPerson;
double* amount; // Pointer to an array
int noOfWeek; // Size of the array
};
Here's my attempted code:
//default constructor
WeeklySales (){
salesPerson="Unknown";
noOfWeek = 13;
amount = 0.00;
}
A compiler auto created default constructor is called a synthesized default constructor. It will initialize the built-in members to 0 or not depends on where the class object is defined? if I define a class
class point{
public:
double x, y;
};
if I define point point1; in global scope then point1.x and point1.y will be initialized to 0, if I define point point2; in a local scope, then its x and y won't be initialized? If it is like this, then I believe if there are built-in type members in a class, then the synthesized default constructor is almost useless!
Code:
activity = new Idle(this, NULL);
class Idle : public Activity {
private:
float mTimeInIdle;
public:
Idle() : mTimeInIdle(0) { }
Idle(Objects *actor, Goods *target) : Activity(actor, target)
{
}
Error 1 error C2514: 'Idle' : class has no constructors d:jackydocumentsvisual studio 2010projectsperfectsimperfectsimperfectsimObjectsObjects.h 43 1 PerfectSim
The activity = new Idle(this, NULL) line is located inside the Objects::Objects(...) constructor.
Would it be caused by some cyclic dependencies? How do I go about resolving it?
I have a question about the default constructor.
To my best understanding, the compiler will provide me with a deafult constructor only if there are no any user defined constructors, at all. Now consider the following code:
Code: class MyClass
{
private:
int m_data;
public:
MyClass(int init):m_data(init){cout<<"Ctr called"<<endl;}
[Code] ....
How is it that suddenly, there is a default constructor?
trying to practice the object-oriented part of it by converting my java programs into c++. I believe I understand the concepts of a header file and declaring the functions in the .cpp files. I keep getting this "Undefined reference to NamedStorm::NamedStorm()" error.
NamedStorm.h
#ifndef NAMEDSTORM_H
#define NAMEDSTORM_H
#include <string>
#include <iostream>
// NEVER use using namespce in header, use std instead.
using std::string;
[code]....
Im trying to create two box in this program using the default constructor. When i call to try and display the info, it says that x, y, and z are not declared in this scope. i wanted to have the user cin the length, height, and width using the void setBox function.
#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
class Box{
public:
[code]....
i tried running my code and i keep getting the error "call to implicitly-deleted default constructor of 'node'. My code is as follows
//.h file
typedef struct node * point
struct node{
string data;
node *next
}
[code]....
I get the error at the line "ptr1 = new node;" I tried putting a default constructor for my node struct and that fixed the problem but a new problem arises. It states that i have a linker error after i compile it with a default constructor.
class Date
Date(int=1, int=1, int=1990);
class Person
Person(string="", string="", Date=NULL);
class RealEstateAgent:Public Person
RealEstateAgent(string="",string="",Date=NULL,Date=NULL,int=NULL, double=0.0);
}
[code]....
how can I assign default values with Customer object and RealEstateAgent?
I was making a template list class, and using it to make list of objects of my own class.It works fine with integers, but not with other classses.
template <typename T>
class CList {
public:
struct Node {
T data;
Node* next;
[code]....
While in AddElement(), it gives error - Default constructor not available.
template<typename T>
bool CList<T>::AddElement(T t) {
bool result = true;
if (head == NULL) {
[code]....
what is wrong here.
For my default constructor I need to set an array of strings to null and the size variable to 0. Here is my code for that
DynamicStringArray::DynamicStringArray() {
*DynamicArray[]=NULL;
size=0;
}
When I try and compile it I get an "expected primary expression before ']' token" error.
I'm not understanding why the string provided for initialization is too long?
Code:
int main()
{
char array[1] = "A";
return 0;
}
So I'm trying to sort an array of 10 elements provided by the user. For Example:
Person 1: 5
Person 2: 3
Person 3: 9
etc etc...
I want it to also pair the value with the person. So it should read:
person 3: 9
Person 1: 5
Person 2: 3
Sort the values in descending order.
I can sort the array, but I cant get the Person number to pair with the value...
1. I designed two classes: Processor and Data.
2. Data represents some data object the user can pass to Processor's public methods.
3. Internally, Processor needs to use InternalData type which is based on the content of Data (I can use Data's public interface to get the required information from it, or construct a Data object using its public constructor when needed, and that's how I have done it so far).
4. To avoid repeating code and localize changes required when Data's interface would change someday, I made conversion functions from Data to InternalData and back inside Processor, as private methods.
Now here comes the kicker:
5. But I'd like these conversions to be implicit inside Processor's methods instead of explicit. And only there.
6. These conversion functions are only for Processor implementation's use. They shouldn't be visible nor accessible from the outside world.
Where the problem lays:
7. InternalData is a library type. I don't have control over it and I cannot modify its interface.
That is, I cannot just add converting constructors or conversion operator member functions to them.You can consider it to be built-in type if you wish.
8. I don't want to put those converters inside Data class either, since it's not its business and it shouldn't know that Processor converts it to something else internally.
Long story short, I'd like to teach the Processor's implementation how to make type conversions between Data and InternalData implicitly, but no one else except Processor should be affected by it. Outside world shouldn't be able to do these conversions or even know about them being done inside Processor's implementation.Is there any way to do it in C++?
The core of the problem seems to be the fact that in C++ defining implicit conversions is possible only from/to a user-defined type when defining this type. I don't know of any way to define such conversions for some other type's internal use only. (Especially when I don't have control about one of these converted types.)
I realize that implicit int rule was removed in C99 but gcc still takes this approach by default. I wonder why this happens:
bbb = 5; // legal
int main(void) {
aaa = 10; // illegal
auto aaa = 10 // legal
Inside function a specifier is needed. Error message with no specifier used is:
error: ‘aaa’ undeclared (first use in this function)
Is this because of linkage - bbb variable has an external linkage so compiler knows that we are defining a variable here while inside mean() we need to show compiler that aaa is defined right here, it does not come from external functions?
i am writing this bank accounts program using structures. i haven't implemented the function before that i want to check if the data is being read and printed. When i build and run the program in visual studio it gives me the following error. "No constructor could take the source type, or constructor overload resolution was ambiguous". Now whats wrong in this program?
/* Bank Accounts Program */
#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>//needed to use system() function
using namespace std;
const int MAX_NUM = 50;
struct Name{
[code]....
Ok, so I'm writing this code and when I build it keeps saying cannot implicitely convert type int to string even though I declared my variables as string. Why is it giving me this error?
private static string Repair()
{
string result="";
string beep;
string spin;
Console.WriteLine("Does your computer beep on startup?:(y,n)");
[Code]...
VS 2012 / Windows 7 64 bit
class
class myclass {
public:
myclass(){/*stuff here*/}
myclass(int* p) {MyPointer = p; myclass()}
[Code] ....
it works until the myclass(int* p) calls myclass()
then the MyPointer will become CCCCCCCC (NULL value)!
is there a way to stop the second constructor from resetting the pointer value to null?
I am trying to write my files to another subfolder . Below is my program.
Code:
cat th6.c
#include <pthread.h>
#include <stdio.h>
#include <string.h>
#define SIZE 8
#define NUMELM 8
[Code] ....
I observe my filename along with directory as text in the new file created in sublfolder. This is output.
[cporgs/apue/threads]: mkdir first
[cporgs/apue/threads]: ./a.out test.txt first
test.txt -- first/test.txt
dfdfdfdfdfdfdf-14
dfdfdfdfdfdfdf-14
in thread test.txt first
[cporgs/apue/threads]: cat first/test.txt
dfdfdfdfdfdfdffirst/test.txt
[cporgs/apue/threads]: cat test.txt
dfdfdfdfdfdfdf
I could not able to get from where this filename and folder is getting added.
I am trying to use constructor within constructor in the same class. Is that possible. I have tried something and it shows me a error message:
error: type "mainClass" is not a direct base of "glavna"
This is the program I tried:
Code:
class mainClass {
private:
int x,y;
Code] ......
Is this example correct? This example from a book
Constructor of the Base Class
Person::Person(char* n="", char* nat="U.S.A", int s=1)
{
name = n;
nationality = nat;
sex = s;
}
Constructor of the Derived Class (inherited from the base class)
Student(char* n, int s=0, char* i=""):
Person(n, s)
Why the initialized list of the base class constructor doesn't match the initialized list of the derived class constructor? I know this book is a little bit old, I'm not sure if this wrong in VC++ 2010?
Following is the code snippet
Code:
[COLOR=white !important]?
1
2
3
4
5 char str1[]="Bombay";
char str2[]="Pune";
char *s1=str,*s2=str2;
while(*s1++=*s2=str2);
printf("%s",str1);
Output of this code comes out to be Pune
But according to me output should be puneay.
Pune should be copied in place of Bomb.and rest should be as it is.
[/COLOR]
I have a problem. I want to set pointers to a default value for both 32 bit and 64 bit compiles. The 32-bit version works as:
enum constants { UNDEFINED = 0xDeadBeef }
if ((unsigned long)ptr == UNDEFINED)
but I can't seem to extend this to 64-bits. I've tried
#if __SIZEOF_POINTER__ == 4
enum constants { UNDEFDATA = 0xDeadBeef };
}; // enum constants
#elif __SIZEOF_POINTER__ == 8
enum constants { UNDEFDATA = 0xDeadBeefDeadBeef };
#endif
with:
if (ptr == UNDEFINED)
but get a message saying the '==' is undefined (I understand this)
Is there any way to setup so that I can change the size of my constants so that the comparisons will always work correctly? I've tried a 'typedef' but the compiler complains at
'typedef unsigned long long ADDR' // won't accept, and
static const SlipCellBase * const TEMPORARY = (SlipCellBase&)0xFFFFFFFFFFFFFFFF; // illegal conversion
enum doesn't work (because it's an int?)
How to create default arguments in C? Is there any way to make default arguments ( i mean any alternative for them).
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