Questions tagged [stdmove]
117 questions
1071
votes
9 answers
What is std::move(), and when should it be used and does it actually move anything?
What is it?
What does it do?
When should it be used?
Good links are appreciated.
Basilevs
- 22,440
- 15
- 57
- 102
26
votes
5 answers
Using an object after std::move doesn't result in a compilation error
After std::move is called on an object, why doesn't the language cause a compilation error if the object is used after?
Is it because it is not possible for compiler to detect this condition?
Jubin Chheda
- 534
- 4
- 11
21
votes
4 answers
What lasts after using std::move c++11
After using std::move in a variable that might be a field in a class like:
class A {
public:
vector&& stealVector() {
return std::move(myVector);
}
void recreateMyVector() {
}
private:
vector myVector; …
Nezquick
- 455
- 4
- 11
19
votes
2 answers
Where to use std::move for strings?
I was reading this post.
And I reached to the following code.
I was wondering:
Is std::move useful for strings (assuming the string is long enough)?
Does it invalidate the previous string?
Where should I use it and where I should not?
.
class…
ar2015
- 5,558
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18
votes
1 answer
Is the front address of std::vector move invariant?
In the following snippet:
std::vector a(100, 4.2);
auto* a_ptr = a.data();
auto b = std::move(a);
auto* b_ptr = b.data();
std::cout << ((b_ptr == a_ptr) ? "TRUE" : "FALSE") << '\n';
does the C++ standard guarantee that b_ptr is always…
Teodor Nikolov
- 783
- 7
- 14
18
votes
4 answers
Should I return an rvalue reference (by std::move'ing)?
A C++Next blog post said that
A compute(…)
{
A v;
…
return v;
}
If A has an accessible copy or move constructor, the compiler may choose to elide the copy. Otherwise, if A has a move constructor, v is moved. Otherwise, if A has a copy…
StereoMatching
- 4,971
- 6
- 38
- 70
16
votes
1 answer
Why to use std::move despite the parameter is an r-value reference
I am confused about using std::move() in below code:
If I uncomment line at (2) the output would be: 1 2 3 but if I uncomment line at (1) output would be nothing which means that move constructor of std::vector was called!
Why do we have to make…
Islam Abdeen
- 539
- 3
- 10
13
votes
1 answer
Why is a std::move of a value from a const std::optional possible?
Why is the following snippet legal C++ code? This is a purely theoretical question - there is no usecase that I have in mind:
#include
#include
#include
int main() {
std::vector v{1, 2, 3};
const…
Markus Moll
- 163
- 8
12
votes
1 answer
Why doesn't C++ move construct rvalue references by default?
Say I have the following function
void doWork(Widget && param) // param is an LVALUE of RRef type
{
Widget store = std::move(param);
}
Why do I need to cast param back to an rvalue with std::move()? Shouldn't it be obvious that the type of…
barney
- 2,172
- 1
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- 25
11
votes
2 answers
Could it be possible to have types with move operations that throw in containers?
While explaining move operations on objects with a colleague, I basically said that move operations should not throw exceptions in a container because if the move operation fails, then there is no way to bring back the original object reliably. …
Adrian
- 10,246
- 4
- 44
- 110
10
votes
1 answer
Why is my code printing rvalue 2 times instead of rvalue & lvalue?
So I wanted to practice the usage of std::forward and created a Test class with 2 constructors. 1 with T& and the other with T&& as overload. T& prints lvalue, and T&& prints rvalue so I know which one of the constructors is being used. I create 2…
3l4x
- 103
- 4
10
votes
3 answers
Using std::move to pass in a temp lambda, or to "pull" out a temp parameter and what is the difference?
I have the following (contrived) code where I have a printer class with a single print function in it and a working class that processes a string and then calls a callback function to the print function:
#include
#include…
code_fodder
- 15,263
- 17
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- 167
7
votes
0 answers
why I can't bind function with rvalue args like this?
#include
#include
#include
#include
using namespace std;
template
void do_task(Func &func, Args &&...args)
{
auto f = bind(func, forward(args)...);
…
Xuan Lin
- 81
- 3
6
votes
3 answers
Assign std::vector to std::vector WITHOUT copying memory
I have a function that returns a std::vector
I am aware that std::byte is not a character type nor an integral type, and that converting it to char is only possible through a typecast. So far so good.
So I would like (in cases where I…
matt
- 95
- 5
6
votes
1 answer
Why does the std::move() work in c++?
Following is the code snippet:
int i=0;
int&&k=std::move(i);
In c++ primer the move is
template
typename remove_reference::type &&move(T&& t)
{return static_cast::type&&>(t);}
As far as i know,this…
user9396941