A delegating constructor is a C++11 feature that allows a class constructor to delegate to another of its constructors in its initializer-list, much like it can call base class constructors.
Questions tagged [delegating-constructor]
24 questions
36
votes
3 answers
How to handle constructors that must acquire multiple resources in an exception safe manner
I've got a non-trivial type that owns multiple resources. How do I construct it in an exception safe manner?
For example, here is a demo class X that holds an array of A:
#include "A.h"
class X
{
unsigned size_ = 0;
A* data_ =…
Howard Hinnant
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11
votes
4 answers
Do C++11 delegated ctors perform worse than C++03 ctors calling init functions?
[this question has been highly edited; pardon that, I've moved the edits into an answer below]
From Wikipedia (subarticle included) on C++11:
This [new delegating constructors feature] comes with a caveat: C++03 considers an object to be…
okovko
- 1,851
- 14
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10
votes
2 answers
Delegating constructor gives segmentation fault when using class field for argument
Actually the segmentation fault happens in another program I tried to compile which happens because of this behaviour.
My question is:
This is a bug or my fault?
Reproducible in any way (even if the something field is private or protected) and…
Memos Electron
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8
votes
2 answers
Crash in constructor with using virtual inheritance and delegating constructors
struct D
{
virtual void m() const = 0;
};
struct D1 : public virtual D { };
struct D2 : public virtual D { };
struct B : public D2
{
B() { }
B(int val) : B() { }
void m() const { }
};
struct A : public B, public D1
{
A() :…
eXXXXXXXXXXX2
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8
votes
1 answer
MSVC direct constructor call extension
In this response, tloveless pointed out that it's possible in MSVC to use this->foo::foo(42); for constructor delegation to directly call a constructor:
#include
struct foo
{
int m;
foo(int p) : m(p) { std::cout <<…
dyp
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7
votes
4 answers
How to forward overloaded constructor call to another constructor in C++/CLI
I know that there is no way to do this in pure C++, but I was wondering if it is possible to call a constructor from another constructor's initialization list in C++/CLI, same way one can do it in C#.
Example:
ref class Foo {
Foo() {}
Foo(int i)…
Yuri Astrakhan
- 8,808
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6
votes
2 answers
Delegating copy constructor and const data initialization
I have a class A with lots of data members, some of which are constant. All data members have proper copy constructors, so I want to default a copy constructor of my class:
class A
{
public:
A() : a(1) {}
A(const A& op) =…
Sergey
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5
votes
3 answers
C++11 constructor delegation with aggregate initialization
Is it possible to invoke aggregate initialization within my own definition of the default ctor?
GCC complains "error: constructor delegates to itself" with the below code:
struct X {
int x, y, z, p, q, r;
X(): x{}, y{}, z{}, p{}, q{}, r{} { } …
nodakai
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5
votes
2 answers
argument's default value base on others
i want to achieve a class like this:
class A{
int a;
int b;
int c;
A():a(),b(),c(){};
A(int ia,int ib,int ic=ia+ib):a(ia),b(ib),c(ic){}; //this is what i need
};
I want the ic's default value is caculated based on the ia and…
Detective King
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4
votes
1 answer
constructor delegates to itself in g++ & clang++
Consider following program. I accidentally made a mistake in it.
struct T {
int s;
T() : T() {
s=9;
}
};
int main() {
T t;
}
The above code compiles & runs fine in some versions of g++ like g++ 4.8.1 (See live demo here ) &…
Destructor
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3
votes
1 answer
C++ delegating constructor with initialization list. Which inits happen?
I've looked at a very similar question, but I'm not quite sure I understand the answer. If I delegate a constructor, which initializations from initialization lists occur?
Example:
MyClass::MyClass(int a, int b)
:
MyClass(a, b,…
turbulencetoo
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2
votes
1 answer
C++ : can I do some processing before calling another constructor?
I have a class with two constructors.
class Foo {
Foo(B b) {... }
Foo(int n) : Foo(buildBFromInt(n)) {} ??
}
The first takes some object and I would like to have a second one that first creates the object from a simpler type. Is this possible…
ElefEnt
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2
votes
3 answers
re-initialise using delegating constructor
I have this class X, using delegating constructor I want to change only the value i and j as 0. Is it possible to do so?
class X{
public:
X() = default;
X(int ival, int jval) : i{ ival }, j{ jval } {}
X(int new_i) : i{ new_i }, X(i,…
abhimanyuaryan
- 3,882
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1
vote
1 answer
C++ Error checking before constructor delegation
I have a constructor that creates a matrix from size_t dimensions, I want to add support for int dimensions. However, before passing the ints to the size_t constructor I would like to make sure that they are positive.
Matrix(vector vals,…
NoamV
- 65
- 5
1
vote
2 answers
Why partially initializing a class and then invoking delegating ctor fails?
Following code does not initialize struct string members to same value.
#include
#include
struct S
{
std::string s1;
std::string s2;
S(std::string const& s) : s1{s}{}
S(int i) : S([&]{
s2 =…
user1832484
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