All Questions
Tagged with c++ inheritance
10,402
questions
1259
votes
17
answers
777k
views
What is the difference between public, private, and protected inheritance?
What is the difference between public, private, and protected inheritance in C++?
user106599
915
votes
17
answers
266k
views
893
votes
17
answers
604k
views
How do you declare an interface in C++?
How do I setup a class that represents an interface? Is this just an abstract base class?
- 21.1k
865
votes
10
answers
1.1m
views
What are the rules for calling the base class constructor?
What are the C++ rules for calling the base class constructor from a derived class?
For example, I know in Java, you must do it as the first line of the subclass constructor (and if you don't, an ...
- 116k
790
votes
9
answers
977k
views
How to call a parent class function from derived class function?
How do I call the parent function from a derived class using C++? For example, I have a class called parent, and a class called child which is derived from parent. Within
each class there is a print ...
- 12.6k
328
votes
8
answers
385k
views
Inheriting constructors
Why does this code:
class A
{
public:
explicit A(int x) {}
};
class B: public A
{
};
int main(void)
{
B *b = new B(5);
delete b;
}
Result in these errors:
main.cpp: In ...
- 13.9k
264
votes
3
answers
32k
views
Why do I have to access template base class members through the this pointer?
If the classes below were not templates I could simply have x in the derived class. However, with the code below, I have to use this->x. Why?
template <typename T>
class base {
protected:
...
- 57.5k
247
votes
6
answers
235k
views
243
votes
13
answers
79k
views
Thou shalt not inherit from std::vector
Ok, this is really difficult to confess, but I do have a strong temptation at the moment to inherit from std::vector.
I need about 10 customized algorithms for vector and I want them to be directly ...
- 132k
198
votes
2
answers
127k
views
C++ inheritance - inaccessible base?
I seem to be unable to use a base class as a function parameter, have I messed up my inheritance?
I have the following in my main:
int some_ftn(Foo *f) { /* some code */ };
Bar b;
some_ftn(&b);
...
- 2,015
184
votes
7
answers
221k
views
How can I initialize base class member variables in derived class constructor?
Why can't I do this?
class A
{
public:
int a, b;
};
class B : public A
{
B() : A(), a(0), b(0)
{
}
};
- 2,385
181
votes
7
answers
93k
views
Why should I declare a virtual destructor for an abstract class in C++?
I know it is a good practice to declare virtual destructors for base classes in C++, but is it always important to declare virtual destructors even for abstract classes that function as interfaces? ...
- 7,926
163
votes
12
answers
101k
views
Is there a way to instantiate objects from a string holding their class name?
I have a file: Base.h
class Base;
class DerivedA : public Base;
class DerivedB : public Base;
/*etc...*/
and another file: BaseFactory.h
#include "Base.h"
class BaseFactory
{
public:
...
- 8,769
157
votes
5
answers
63k
views
Initialize parent's protected members with initialization list (C++)
Is it possible to use the initialization list of a child class' constructor to initialize data members declared as protected in the parent class? I can't get it to work. I can work around it, but it ...
- 3,545
153
votes
6
answers
56k
views
What is the point of a private pure virtual function?
I came across the following code in a header file:
class Engine
{
public:
void SetState( int var, bool val );
{ SetStateBool( int var, bool val ); }
void SetState( int var, int val );
...
- 11.3k
143
votes
6
answers
237k
views
Inheriting from a template class in c++
Let's say we have a template class Area, which has a member variable T area, a T getArea() and a void setArea(T) member functions.
I can create an Area object of a specific type by typing Area<int&...
- 1
124
votes
5
answers
102k
views
How does virtual inheritance solve the "diamond" (multiple inheritance) ambiguity?
class A { public: void eat(){ cout<<"A";} };
class B: virtual public A { public: void eat(){ cout<<"B";} };
class C: virtual public A { public: void eat(){ cout&...
- 10.6k
122
votes
5
answers
103k
views
Do ALL virtual functions need to be implemented in derived classes?
This may seem like a simple question, but I can't find the answer anywhere else.
Suppose I have the following:
class Abstract {
public:
virtual void foo() = 0;
virtual void bar();
}
class ...
- 2,164
115
votes
5
answers
89k
views
How to use base class's constructors and assignment operator in C++?
I have a class B with a set of constructors and an assignment operator.
Here it is:
class B
{
public:
B();
B(const string& s);
B(const B& b) { (*this) = b; }
B& operator=(const ...
- 27k
110
votes
3
answers
36k
views
Does Qt support virtual pure slots?
My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget.
Recently, I realized that all these classes share 2 commons slots (loadSettings() and ...
- 54.8k
107
votes
7
answers
69k
views
Are static fields inherited?
When static members are inherited, are they static for the entire hierarchy, or just that class, i.e.:
class SomeClass
{
public:
SomeClass(){total++;}
static int total;
};
class ...
user98188
102
votes
2
answers
50k
views
Function with same name but different signature in derived class not found
I have a function with the same name, but with different signature in a base and derived classes. When I am trying to use the base class's function in another class that inherits from the derived, I ...
- 27k
102
votes
9
answers
69k
views
Why does C++ not allow inherited friendship?
Why is friendship not at least optionally inheritable in C++? I understand transitivity and reflexivity being forbidden for obvious reasons (I say this only to head off simple FAQ quote answers), but ...
99
votes
4
answers
24k
views
`std::variant` vs. inheritance vs. other ways (performance)
I'm wondering about std::variant performance. When should I not use it? It seems like virtual functions are still much better than using std::visit which surprised me!
In "A Tour of C++" ...
- 1,967
98
votes
1
answer
36k
views
conversion from derived * to base * exists but is inaccessible
Why does the follwing code produce this error even though c is a struct and has a public inheritance by default??
struct c
{
protected:
int i;
public:
c(int ii=0):i(ii){}
virtual c *fun()...
- 5,491
97
votes
7
answers
93k
views
Inheritance: 'A' is an inaccessible base of 'B'
$ cat inheritance.cpp
#include <iostream>
using namespace std;
class A { };
class B : private A { };
int main() {
A* ab = new B;
}
$
$ g++ inheritance.cpp
inheritance.cpp: In function '...
- 92.6k
93
votes
3
answers
67k
views
C++ virtual function return type
Is it possible for an inherited class to implement a virtual function with a different return type (not using a template as return)?
- 10k
92
votes
5
answers
55k
views
In C++, is it possible to forward declare a class as inheriting from another class?
I know that I can do:
class Foo;
but can I forward declare a class as inheriting from another, like:
class Bar {};
class Foo: public Bar;
An example use case would be co-variant reference return ...
- 41.8k
91
votes
9
answers
45k
views
Default inheritance access specifier
If I have for example two classes A and B, such that class B inherits A as follows:
class B: public A
In this case, I'm doing public inheritance.
If I write the previous code as follows:
class B: ...
- 48.3k
91
votes
3
answers
60k
views
Derived template-class access to base-class member-data
This question is a furtherance of the one asked in this thread.
Using the following class definitions:
template <class T>
class Foo {
public:
Foo (const foo_arg_t foo_arg) : _foo_arg(...
- 2,172
90
votes
5
answers
32k
views
Are virtual destructors inherited?
If I have a base class with a virtual destructor. Has a derived class to declare a virtual destructor too?
class base {
public:
virtual ~base () {}
};
class derived : base {
public:
virtual ~...
- 8,693
89
votes
6
answers
155k
views
Using C++ base class constructors?
While working with templates I ran into a need to make a base class constructors accessible from inherited classes for object creation to decrease copy/paste operations.
I was thinking to do this ...
- 1,027
88
votes
1
answer
21k
views
Why is Default constructor called in virtual inheritance?
I don't understand why in the following code, when I instanciate an object of type daughter, the default grandmother() constructor is called ?
I thought that either the grandmother(int) constructor ...
- 982
85
votes
20
answers
30k
views
Why can't I inherit from int in C++?
I'd love to be able to do this:
class myInt : public int
{
};
Why can't I?
Why would I want to? Stronger typing. For example, I could define two classes intA and intB, which let me do intA + intA ...
- 5,829
84
votes
9
answers
52k
views
C++: Can a struct inherit from a class?
I am looking at the implementation of an API that I am using.
I noticed that a struct is inheriting from a class and I paused to ponder on it...
First, I didn't see in the C++ manual I studied ...
- 14.6k
81
votes
5
answers
17k
views
C++ static polymorphism (CRTP) and using typedefs from derived classes
I read the Wikipedia article about the curiously recurring template pattern in C++ for doing static (read: compile-time) polymorphism. I wanted to generalize it so that I could change the return types ...
- 1,136
80
votes
5
answers
51k
views
Why should I use the "using" keyword to access my base class method?
I wrote the below code in order to explain my issue. If I comment the line 11 (with the keyword "using"), the compiler does not compile the file and displays this error: invalid conversion from 'char' ...
- 1,804
79
votes
7
answers
110k
views
C++ Constructor/Destructor inheritance
EDIT : Summary of answers
In the following, B is a subclass of A.
It's a matter of terminology; ctors and dtors are not inherited, in the sense that the ctor/dtor of B will not be borrowed from A's ...
- 7,761
78
votes
4
answers
201k
views
C++ cast to derived class
How can i cast to a derived class? The below approaches all give the following error:
Cannot convert from BaseType to DerivedType. No constructor could take
the source type, or constructor ...
- 4,772
75
votes
8
answers
54k
views
Prevent class inheritance in C++
Recently one of my friend asked me how to prevent class inheritance in C++. He wanted the compilation to fail.
I was thinking about it and found 3 answers. Not sure which is the best one.
1) Private ...
- 811
75
votes
1
answer
77k
views
virtual inheritance [duplicate]
What is the meaning of "virtual" inheritance?
I saw the following code, and didn't understand the meaning of the keyword virtual in the following context:
class A {};
class B : public virtual A;
- 8,769
74
votes
11
answers
30k
views
What's the point of a final virtual function?
Wikipedia has the following example on the C++11 final modifier:
struct Base2 {
virtual void f() final;
};
struct Derived2 : Base2 {
void f(); // ill-formed because the virtual function ...
- 260k
73
votes
7
answers
34k
views
Propagating 'typedef' from based to derived class for 'template'
I'm trying to define base class, which contains typedef's only.
template<typename T>
class A
{
public:
typedef std::vector<T> Vec_t;
};
template<typename T>
class B : public A&...
- 27.2k
73
votes
7
answers
63k
views
Are static variables in a base class shared by all derived classes?
If I have something like
class Base {
static int staticVar;
}
class DerivedA : public Base {}
class DerivedB : public Base {}
Will both DerivedA and DerivedB share the same staticVar or will ...
- 278k
71
votes
1
answer
29k
views
What is constructor inheritance?
In C++11, what is meant by inheriting the constructor? If it is what i think it is (Base class constructor is brought in the scope of the derived class), what are its implications on my code? What are ...
- 4,805
70
votes
8
answers
45k
views
Why do we actually need Private or Protected inheritance in C++?
In C++, I can't think of a case in which I would like to inherit private/protected from a
base class:
class Base;
class Derived1 : private Base;
class Derived2 : protected Base;
Is it really useful?...
- 8,769
70
votes
8
answers
25k
views
Why should one not derive from c++ std string class?
I wanted to ask about a specific point made in Effective C++.
It says:
A destructor should be made virtual if a class needs to act like a polymorphic class. It further adds that since std::string ...
- 2,673
67
votes
6
answers
160k
views
Why does the base class constructor of a derived type get called?
#include <iostream>
#include <stdio.h>
using namespace std;
// Base class
class Shape
{
public:
void setWidth(int w)
{
width = w;
}
void setHeight(...
- 14.7k
63
votes
6
answers
34k
views
62
votes
5
answers
50k
views
Can't downcast because class is not polymorphic?
Is it possible to have inheritance with no virtual methods? The compiler is saying that the following code is not polymorphic.
Example:
class A {
public:
int a;
int getA(){return a;};
}
class ...
- 7,546