move-semantics Questions
2
Are the move semantics used in Example A necessary, and which struct is superior?
Example A:
struct A
{
std::string a;
A( std::string a ) : a( std::move(a) ){ }
};
Example B:
struct B
{
std...
Madalene asked 4/4, 2017 at 1:24
4
Solved
In C++, is it OK to steal resources from a map that I do not need afterwards anymore? More precisely, assume I have a std::map with std::string keys and I want to construct a vector out of it by st...
Neophyte asked 22/2, 2020 at 7:15
3
Solved
Consider the code below
void foo(std::vector<int> v)
{
//do something here
}
//calling the function
vector<int> v1 = {1,2,3};
foo(std::move(v1));
My question is, isn't the function ...
Respiration asked 20/1, 2020 at 20:52
7
Solved
I'm a bit confused regarding the difference between push_back and emplace_back.
void emplace_back(Type&& _Val);
void push_back(const Type& _Val);
void push_back(Type&& _Val);
...
Monteria asked 29/11, 2010 at 12:4
3
Solved
http://www.drdobbs.com/cpp/practical-c-error-handling-in-hybrid-env/197003350?pgno=4
In this article Herb Sutter explains that throwing an exception requires a copy of the exception as it's create...
Plenty asked 25/8, 2012 at 13:18
2
Solved
I was reading a book about data structure implemented in C++, I dont understand a code snippet， it's part of vector class
void push_back(object &&x) {
//do something
objects[size++] = s...
Grubb asked 8/11, 2019 at 5:54
3
Solved
In C++11, value parameters (and other values) enjoy implicit move when returned:
A func(A a) {
return a; // uses A::A(A&&) if it exists
}
At least in MSVC 2010, rvalue reference paramet...
Pyromania asked 19/3, 2012 at 22:49
2
Solved
Removing the comment from following code gives a compile time error. It seems that defining the destructor in derived class is causing the copy constructor to be called in emplace_back
#include &l...
Tendril asked 9/10, 2019 at 22:30
1
Solved
As said by cppreference.com,
Maps are usually implemented as red-black trees.
So moving a std::map is just moving the pointer to the root node + other information such as size. Why is std::ma...
Larrisa asked 31/7, 2019 at 21:54
1
Solved
Taking as example
void f(B b, A&& a) {...}
B g(B b, A a) {...}
int main() {
B b;
A a;
f(g(b, a), std::move(a));
}
I presume this would be valid code seeing as an std::move() is merel...
Muslin asked 21/7, 2019 at 10:27
1
The standard mandates that the move assignment operator of optional ...
constexpr optional& operator=( optional&& other )
[...] shall not participate in overload resolution unless...
Sello asked 18/3, 2019 at 20:49
2
Solved
Consider the following class Buffer, which contains an std::vector object:
#include <vector>
#include <cstddef>
class Buffer {
std::vector<std::byte> buf_;
protected:
Buffer(s...
Wieland asked 14/7, 2019 at 14:44
2
Solved
Inspired by the post Why does destructor disable generation of implicit move methods?, I was wondering if the same is true for the default virtual destructor, e.g.
class WidgetBase // Base class o...
Extort asked 27/11, 2015 at 12:4
1
Solved
Standard specifies that STL containers, after begin moved (in this case we talk about std::move that enables move construction / assignment), are in valid, but unspecified state.
I belive th...
Winna asked 12/7, 2019 at 13:53
1
Solved
I have run into a problem that a move constructor of a superclass did not get invoked properly when its subclass has an explicitly defaulted destructor. The move constructor does get invoked when t...
Shopper asked 10/7, 2019 at 10:10
4
Solved
An unique_ptr cannot be pushed back into a std::vector since it is non-copyable, unless std::move is used. However, let F be a function that returns a unique_ptr, then the operation std::vector::pu...
Rheology asked 7/7, 2019 at 20:37
5
Solved
When implementing move constructors and move assignment operators, one often writes code like this:
p = other.p;
other.p = 0;
The implicitly defined move operations would be implemented with cod...
Shogunate asked 26/2, 2012 at 10:55
1
Solved
Let's consider the following code:
class X {
std::vector<int> _v;
public:
X(std::vector<int>&& v): _v(std::move(v)) {}
};
The compiler calls this constructor only for objec...
Popelka asked 30/6, 2019 at 18:24
1
I originally assumed that it is bad practice to move an l-value reference parameter. Is this indeed commonly agreed by the C++ developer community?
When I call a function that has an R-value refer...
Welterweight asked 24/6, 2019 at 13:20
1
Solved
The following code
using vptr = std::vector<std::unique_ptr<int>>;
auto m = std::unordered_map<int, std::any>{};
m.try_emplace(0, move(vptr{}));
Fails to compile, complaining a...
Pentacle asked 29/5, 2019 at 22:12
2
Solved
I'm trying to understand Item 17 from "Effective Modern C++" about special member function generation so I was trying some examples and am trying to reason about some behavior. In the book it says:...
Litchfield asked 21/5, 2019 at 15:48
2
I have a class in my C++ code which has its own move constructor. A simplified version is shown here:
class myClass {
//In this example, myClass must manually manage allocating
//and freeing a m...
Enchondroma asked 19/5, 2019 at 0:37
2
Solved
I am currently learning more about all the c++11/14 features and wondering when to use std::move in function calls.
I know I should not use it when returning local variables, because this bre...
Cornall asked 26/4, 2019 at 10:1
3
Solved
I have some code in which I want to make absolutely sure that a moved-from std::vector will not leave secret data around (think about crypto key management). In my class' move constructor, I do som...
Female asked 7/3, 2019 at 23:1
6
Solved
I'm trying to understand rvalue references and move semantics of C++11.
What is the difference between these examples, and which of them is going to do no vector copy?
First example:
std::vector<...
Heliacal asked 13/2, 2011 at 20:28
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