Initializes an object from another object
Questions tagged [copy-initialization]
52 questions
21
votes
2 answers
When should you use direct initialization and when copy initialization?
Is it simply preference or are there specific instances where one is necessary over another? I'm refering to the following variants for initialization
T t(e); // direct initialization
T t = e; // copy initialization
Mike
- 219
- 2
- 3
14
votes
2 answers
Copy initialization of the form '= {}'
Given the following:
#include
class X;
class Y
{
public:
Y() { printf(" 1\n"); } // 1
// operator X(); // 2
};
class X
{
public:
X(int) {}
X(const Y& rhs) { printf(" 3\n"); } // 3
X(Y&& rhs) { printf(" 4\n"); } …
Rich
- 185
- 1
- 6
13
votes
1 answer
Which of these conversions should be ambiguous?
I have some code like the following:
class bar;
class foo
{
public:
operator bar() const;
};
class bar
{
public:
bar(const foo& foo);
};
void baz() {
foo f;
bar b = f; // [1]
const foo f2;
bar b2 = f2; // [2]
}
GCC…
Tavian Barnes
- 12,477
- 4
- 45
- 118
11
votes
2 answers
Why does copy initializaton require destructor in C++17 with guaranteed move/copy elision?
The following code compiles with MSVC (/permissive-) and fails to compile with GCC/Clang for m_ptr1 and m_ptr2.
#include
struct ForwardDeclared;
class A {
public:
explicit A();
~A();
private:
…
JVApen
- 11,008
- 5
- 31
- 67
10
votes
1 answer
Does copy list initialization invoke copy ctor conceptually?
Before C++11, we can do copy initialization by writing something like A a = 1; which is more or less equivalent to A a = A(1);. That is, a temporary is first created and then a copy ctor is invoked. Regardless of copy elision, this must be so…
Lingxi
- 14,579
- 2
- 37
- 93
9
votes
1 answer
Reference binding through ambiguous conversion operator
#include
using namespace std;
struct CL2
{
CL2(){}
CL2(const CL2&){}
};
CL2 cl2;
struct CL1
{
CL1(){}
operator CL2&(){cout<<"operator CL2&"; return cl2;}
operator const CL2&(){cout<<"operator const CL2&"; return…
Denis
- 2,786
- 1
- 14
- 29
8
votes
6 answers
Strange behavior of copy-initialization, doesn't call the copy-constructor!
I was reading the difference between direct-initialization and copy-initialization (§8.5/12):
T x(a); //direct-initialization
T y = a; //copy-initialization
What I understand from reading about copy-initialization is that it needs accessible &…
Nawaz
- 353,942
- 115
- 666
- 851
8
votes
1 answer
Why is copy initialization the way it is? Why require the copy constructor?
Possible Duplicate:
What’s the motivation behind having copy and direct initialization behave differently?
And by copy initialization, I mean like so:
struct MyStruct
{
MyStruct(int) {}
MyStruct(const MyStruct&) {}
};
MyStruct s = 5; //…
Cornstalks
- 37,137
- 18
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- 144
6
votes
1 answer
Can not-copyable class be caught by value in C++?
In the next program, struct B with deleted copy-constructor is thrown and caught by value:
struct B {
B() = default;
B(const B&) = delete;
};
int main() {
try {
throw B{};
}
catch( B ) {
}
}
Clang rejects the code…
Fedor
- 17,146
- 13
- 40
- 131
6
votes
2 answers
copy initialization - conversion from 'int' to non-scalar type
I would like to know how I should define the class my_int so that the cast from int to std::complex< my_int > is done by the compiler instead of manually by me.
The following program does not compile if 4 is not casted to "my_int"
// Example…
rual93
- 553
- 4
- 11
6
votes
1 answer
This is not copy-initializing, or is it?
In the following code I am not allowed to declare an explicit ctor because the compiler says I am using it in a copy-initializing context (clang 3.3 and gcc 4.8).
I try to prove the compilers wrong by making the ctor non explicit and then declaring…
Patrick Fromberg
- 1,313
- 11
- 37
6
votes
2 answers
Is it possible to infer template parameters of tuple from brace-type initialization?
In this example, is it possible to allow the deduction of the template parameters type of the tuple?
#include
#include
template
void fun(std::tuple t, std::string other){}
int main(){
…
alfC
- 14,261
- 4
- 67
- 118
4
votes
1 answer
Why smart pointer type member variable can't be initialized at the declaring place in a class?
When I want to add a member variable with smart pointer type to a class, I found that it can't be initialized at the declaring place:
class Foo {
public:
std::shared_ptr intSharedPtr = new int; // not ok
Foo() {}
};
But I can do…
Zhang Zheng
- 91
- 5
4
votes
1 answer
Initialization in return statements of functions that return by-value
My question originates from delving into std::move in return statements, such as in the following example:
struct A
{
A() { std::cout << "Constructed " << this << std::endl; }
A(A&&) noexcept { std::cout << "Moved " << this << std::endl; }
…
Ruperrrt
- 489
- 2
- 13
4
votes
1 answer
Why does copy initialization of my class not work with string_view using string literals?
I have the following code:
#include
class Foo
{
public:
Foo(std::string_view) {}
};
When I do this, everything compiles fine (using clang v8, C++17):
Foo f("testing");
However, if I use copy initialization it fails:
Foo f =…
void.pointer
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