Questions tagged [copy-assignment]
146 questions
4
votes
2 answers
Implementing valuelike copy-assignment operator
In C++ Primer there is an example of using the copy-control members to make a class act "valuelike"; that is, when copying the object, the copies are independent. It proposes the following code:
class HasPtrValue
{
public:
HasPtrValue(const…
JamesLens
- 447
- 6
- 14
4
votes
2 answers
Will objects be copied in assignment in D?
When I assign an object in D, will it be copied?
void main() {
auto test = new Test(new Object());
tset.obj;
}
class Test {
public Object obj;
public this(Object ref origObj) {
obj = origObj; // Will this copy origObj into…
Jeroen
- 15,257
- 12
- 59
- 102
4
votes
1 answer
In C++, does a constructor that takes the base class count as a copy constructor?
For example:
class Derived : public Base
{
Derived(const Base &rhs)
{
// Is this a copy constructor?
}
const Derived &operator=(const Base &rhs)
{
// Is this a copy assignment operator?
}
};
Does the…
Matt
- 21,026
- 18
- 63
- 115
3
votes
3 answers
parameter pack templated constructor deletes copy assignment
Trying to understand why having a parameter pack templated constructor for a class apparently causes both the copy constructor and the copy assignment operator to be optimized out. (Actually I can see how the compiler wouldn't be able to discern…
user1470475
- 71
- 4
3
votes
1 answer
Effect of user deleted auto constructors on implicit generation of copy constructors
How does user deleted auto constructors affect implicit generation of copy constructors?
For eg:
struct Foo {
Foo(X) = delete;
auto operator=(X) = delete;
};
int main() {
Foo a;
Foo b(a);
b = a;
}
In the above struct, if X is…
Sourav Kannantha B
- 2,860
- 1
- 11
- 35
3
votes
0 answers
In C++, placement new and copy constructor implementing copy assignment operator, is it a good practice?
Given the code
struct Foo{
Foo(const Foo &other){
i = other.i;
};
Foo &operator=(const Foo &other){
if(this == &other){
return (*this);
}
new (this) Foo(other);
return (*this);
};
int i = 0;
};
struct Bar{
…
Theo Mars
- 41
- 4
3
votes
3 answers
Why does the address of the assigned object not change in C++?
In this C++ example, a class C has a default constructor, a copy constructor and an assignment operator:
struct C {
C();
C(const C& c);
C& operator=(const C& c);
};
The implementation is as follows with some output for tracking the…
TMOTTM
- 3,286
- 6
- 32
- 63
3
votes
2 answers
How to explicitely make a deep copy of an array in MATLAB?
For example, I want to do a deep copy of a to b:
>> a=zeros(2,3);
>> b=a;
So here = creates only a shallow copy. My question is, how to generate a deep copy in this case? I know that I can add a command like
b(1,1)=b(1,1)
to make it a deep copy.…
f. c.
- 1,095
- 11
- 26
3
votes
2 answers
Is assiging a shared_ptr to itself safe?
Is it safe to self-assign a std::shared_ptr? So here is an example:
std::shared_ptr> pVec = std::make_shared>();
std::cout << pVec.use_count() << std::endl; // 1
pVec = pVec;
I know that assigning…
Itachi Uchiwa
- 3,044
- 12
- 26
3
votes
3 answers
C++ declare a move/copy operation will suppress generation of related operations?
I saw a sentence in The C++ programing language which I'm confused with:
• If the programmer declares a copy operation, a move operation, or a destructor for a class,no copy operation, move operation, or destructor is generated for that class.
I…
Frank
- 107
- 6
3
votes
1 answer
fill insert() - copy constructor and copy assignment noexcept status?
Are STL container elements required to have noexcept copy-constructors and copy-assignment operators? Please provide a reference if possible.
If not, what is the state of a STL container when an exception happens during a multi-insert, e.g. during…
dhke
- 15,008
- 2
- 39
- 56
3
votes
5 answers
Why should the parameter to a copy assignment operator should be a reference?
"opperator= should takes a parametor of the (of course,const best) ref of src obj",i see this in many books,but i try to use non-ref instead,it also works!so,whats the purpose of using ref?is it just to avoid copy from the param? my test code…
aishuishou
- 83
- 7
3
votes
1 answer
Assigning array carrying a reference to a new array permits writing to the reference without accessing the original variable assigned to the reference
$a = [1 => "A"];
$b = &$a[1];
$c = $a;
$c[1] = "C";
echo $a[1];
Output : C (But I am expecting the output to be A)
Apparently, array is not referenced by = sign.
$c = $a; <- this should make a copy of $a and assign it to $c, but why does reference…
user2816220
- 43
- 1
- 3
3
votes
1 answer
Automation between containers of different objects with copy assign
I have a sparse vector of type std::vector> where SparseElement is:
template
struct SparseElement
{
I index;
T value;
//............
SparseElement &operator=(const…
Chameleon
- 1,804
- 2
- 15
- 21
2
votes
2 answers
C++ How to store object in arrays without them deleted
I want to seek help on this issue I encountered when learning C++. I tried to store objects into an array directly, but realize the objects gets deconstructed right away. I could not figure out why exactly is this so.
#include
class…
Kay.Z
- 43
- 4