[英]Code blocks & lambdas c++11
please, can any one explain me, how conditionalVariable will be stored in this case, to be used while check_calls_on_current_floor calling outside the condition block? 请问谁能解释我,在这种情况下将如何存储conditionalVariable,以便在condition_block外部调用check_calls_on_current_floor时使用?
std::function<bool()> check_calls_on_current_floor;
if (/*Some condition*/)
{
const int conditionalVariable = /*some value*/;
check_calls_on_current_floor = [&](){
return conditionalVariable == 10; };
}
check_calls_on_current_floor();
It seems like in this case we, can access this variable outside the condition block, in case we got lambda from there. 似乎在这种情况下,我们可以在条件块之外访问此变量,以防我们从那里获取lambda。
It's a dangling reference. 这是一个悬而未决的参考。 It's undefined behavior to make that call after the
if
block. 在
if
块之后进行调用是未定义的行为。 It's very similar to returning a reference to a local variable from a function. 这与从函数返回对局部变量的引用非常相似。 It's even more similar to this:
与此类似:
struct ref_holder
{
ref_holder(const int & r) :ref(r) {}
const int & ref;
};
int main()
{
std::unique_ptr<ref_holder> ptr;
if (true)
{
const int conditionalVariable = 10;
ptr.reset(new ref_holder(conditionalVariable));
}
ptr->ref == 10; // undefined behavior
}
It's somewhat analogous to this: 这有点类似于:
int x = 0;
int* z = &x;
if (condition)
{
int y = 1;
z = &y;
}
If the condition holds, then z
will be pointing to y
which has gone out of scope. 如果条件成立,则
z
将指向超出范围的y
。
This conditionalVariable out of it's scope but in extent. 此conditionalVariable超出其范围,但在一定程度上。
I think this will help you. 我认为这会对您有所帮助。 http://en.wikipedia.org/wiki/Variable_(computer_science)#Scope_and_extent
http://en.wikipedia.org/wiki/Variable_(computer_science)#Scope_and_extent
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