valarray
类看起来与array
类相同,你能解释一下我在哪里更喜欢valarray
不是array
,反之亦然?
valarray
was already in C++03, array
is new in C++11 valarray
is variable length, array
is not. valarray
is designed for numeric computations and provides plenty of operations including +
, -
, *
, cos
, sin
, etc... array
does not. valarray
has an interface to retrieve slices of the array (sub arrays), array
does not. The class templates related to std::valarray<T>
are intended to support optimizations techniques known as expression templates . I haven't tried to do this but my understanding is that the specification doesn't quite require this and also doesn't really support this sufficiently. In general std::valarray<T>
is a fairly specialized class and it isn't really broadly used. Also, I think the template arguments support for std::valarray<T>
are a limited set (eg the numeric built-in types).
On the other std::array<T, n>
is a fixed size array supporting, as far as possible while being fixed size, the normal container interface. Essentially, std::array<T>
is a more convenient to use version of T[n]
.
valarray
is a dynamic data structure, whose size can change at runtime and which performs dynamic allocation. array
is a static data structure whose size is determined at compile time (and it is also an aggregate).
Don't use valarray
, though; just use a vector
instead.
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