是否象这种2D病媒(在5x4 2D vectro中的所有数值均已初步确定为3)?
std::vector<std::vector<int> > foo(5, std::vector<int>(4, 3));
这似乎有oka,但是,在任何地方,我看着网络的人似乎都建议把这种媒介引入 lo和推回。 起初,我担心,这里的所有各行都将指同一种病媒,但情况似乎并非如此。 我失踪了吗?
这完全是有效的——你获得2D矢量([5,4]元素,每个元素都初始到3。
在其他大多数情况下(例如,在你想要不同要素的不同价值观的地方),你不能使用任何一行——因此需要假体。
守则是有效的,确实是你想要做到的(假定我正确理解你的意图)。
然而,这样做一般效率不高(至少在目前语言/图书馆版本中)。 以上初始化形成一种临时病媒,然后将单个子主推为copying。 这可能相当低的效率。 由于这一原因,在许多情况下,最好自行建造顶级病媒。
std::vector<std::vector<int> > foo(5);
之后,通过做像样的事情,在本地建造自己的小子。
foo[i].resize(4, 3);
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