std::valarray<T>:: operator=
From cppreference.com
|
valarray
<
T
>
&
operator
=
(
const
valarray
<
T
>
&
other
)
;
|
(1) | |
|
valarray
<
T
>
&
operator
=
(
valarray
<
T
>
&&
other
)
noexcept
;
|
(2) | (since C++11) |
|
valarray
<
T
>
&
operator
=
(
const
T
&
val
)
;
|
(3) | |
|
valarray
<
T
>
&
operator
=
(
const
std::
slice_array
<
T
>
&
other
)
;
|
(4) | |
|
valarray
<
T
>
&
operator
=
(
const
std::
gslice_array
<
T
>
&
other
)
;
|
(5) | |
|
valarray
<
T
>
&
operator
=
(
const
std::
mask_array
<
T
>
&
other
)
;
|
(6) | |
|
valarray
<
T
>
&
operator
=
(
const
std::
indirect_array
<
T
>
&
other
)
;
|
(7) | |
|
valarray
<
T
>
&
operator
=
(
std::
initializer_list
<
T
>
il
)
;
|
(8) | (since C++11) |
Replaces the contents of the numeric array.
1)
Copy assignment operator. If
size
(
)
!
=
other.
size
(
)
, first resizes
*
this
as if by
resize
(
other.
size
(
)
)
. Each element of
*
this
is assigned the value of the corresponding element of
other
.
2)
Move assignment operator. Replaces the contents of
*
this
with those of
other
. The value of
other
is unspecified after this operation. The complexity of this operation may be linear if T has non-trivial destructors, but is usually constant otherwise.
3)
Replaces each value in
*
this
with a copy of
val
.
4-7)
Replaces the contents of
*
this
with the result of a generalized subscripting operation. The behavior is undefined if
size()
does not equal the length of
other
or if any value on the left depends on the value on the right (e.g.
v
=
v
[
v
>
2
]
).
8)
Assigns the contents of initializer list
il
. Equivalent to
*
this
=
valarray
(
il
)
.
Parameters
| other | - | another numeric array (or a mask) to assign |
| val | - | the value to initialize each element with |
| il | - | initializer list to assign |
Return value
* this
Exceptions
1,3-8)
May throw implementation-defined exceptions.
Example
Run this code
#include <iomanip> #include <iostream> #include <valarray> void print(const char* rem, const std::valarray<int>& v) { std::cout << std::left << std::setw(36) << rem << std::right; for (int n : v) std::cout << std::setw(3) << n; std::cout << '\n'; } int main() { std::valarray<int> v1(3); v1 = -1; // (3) from a scalar print("assigned from scalar: ", v1); v1 = {1, 2, 3, 4, 5, 6}; // (8): from initializer list of different size print("assigned from initializer_list:", v1); std::valarray<int> v2(3); v2 = v1[std::slice(0, 3, 2)]; // (4): from slice array print("every 2nd element starting at pos 0:", v2); v2 = v1[v1 % 2 == 0]; // (6): from mask array print("values that are even:", v2); std::valarray<std::size_t> idx = {0, 1, 2, 4}; // index array v2.resize(4); // sizes must match when assigning from gen subscript v2 = v1[idx]; // (7): from indirect array print("values at positions 0, 1, 2, 4:", v2); }
Output:
assigned from scalar: -1 -1 -1 assigned from initializer_list: 1 2 3 4 5 6 every 2nd element starting at pos 0: 1 3 5 values that are even: 2 4 6 values at positions 0, 1, 2, 4: 1 2 3 5
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 624 | C++98 |
the behaviors of overloads
(4-7)
were
unclear if the length of other is not
size()
|
the behaviors are
undefined in this case |
| LWG 630 | C++98 |
the behavior of the copy assignment operator
was undefined if size ( ) ! = other. size ( ) |
resizes
*
this
first in this case |
| LWG 2071 | C++11 |
the move assignment operator resized
* this if size ( ) ! = other. size ( ) |
not required to
resize in this case |