Warning C26800
Use of a moved from object: 'object'.
Remarks
Warning C26800 is triggered when a variable is used after it has been moved from. A variable is considered moved from after it's passed to a function as rvalue reference. There are some exceptions for assignment, destruction, and some state resetting functions such as std::vector::clear
. After using a state resetting function, we're free to use the variable. This check only reasons about the local variables.
The following methods are considered state resetting methods:
- Functions with the following case-insensitive substring in their name:
clear
,clean
,reset
,free
,destroy
,release
,dealloc
,assign
- Overloaded assignment operators, destructor
This check respects the std::swap
operation:
void f() {
Y y1, y2;
consume(std::move(y1));
std::swap(y1, y2);
y1.method(); // OK, valid after swap.
y2.method(); // warning C26800
}
The check also supports the try_emplace
operations in STL that conditionally move its argument:
int g() {
std::map<int, Y> m;
Y val;
auto emplRes = m.try_emplace(1, std::move(val));
if (!emplRes.second) {
val.method(); // No C26800, val was not moved because the insertion did not happen.
}
}
Code analysis name: USE_OF_A_MOVED_FROM_OBJECT
Examples
The following code generates C26800.
#include <utility>
struct X {
X();
X(const X&);
X(X&&);
X &operator=(X&);
X &operator=(X&&);
~X();
};
template<typename T>
void use_cref(const T&);
void test() {
X x1;
X x2 = std::move(x1);
use_cref(x1); // warning C26800
}
The following code doesn't generate C26800.
#include <utility>
struct MoveOnly {
MoveOnly();
MoveOnly(MoveOnly&) = delete;
MoveOnly(MoveOnly&&);
MoveOnly &operator=(MoveOnly&) = delete;
MoveOnly &operator=(MoveOnly&&);
~MoveOnly();
};
template<typename T>
void use(T);
void test() {
MoveOnly x;
use(std::move(x)); // no 26800
}
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