Question

I have a piece of performance critical code written with pointers and dynamic memory. I would like to rewrite it with STL containers, but I m a bit concerned with performance. Is there a way to increase the size of a container without initializing the data?

例如,不这样做

ptr = new BYTE[x];

我想做的是这样的事情。

vec.insert(vec.begin(), x, 0);

However this initializes every byte to 0. Isn t there a way to just make the vector grow? I know about reserve() but it just allocates memory, it doesn t change the size of the vector, and doesn t allows me to access it until I have inserted valid data.

谢谢大家。

Answer 1

<代码>vec.resize (newsize )的定义是,其效果与

vec.insert( vec.end(), newsize - vec.size(), T() )

如果newsize > vec.size(......,但汇编者可能难以确定其正在增长,而不是缩小,而且其数量如何。你可以尝试对两者进行定性分析。

如果你确信违约的初始阶段需要时间,就会与你自己的建筑商明确消除。 (即使含蓄的构造者被罚款,也能够显示意图。)

struct BYTE {
    char v;
    BYTE() {} // no default initialization!
    BYTE( char x ) : v(x) {}
    operator char&() { return v; }
    operator char const&() const { return v; }
    char *operator&() { return &v; } // not sure about operator&...
    char const *operator&() const { return &v; } // probably good in this case
};

Answer 2

vector.resize(......) 或许会有帮助? 你可以具体说明你想要达到(规模更大或较小)的面积,也使你想要成为新内容的人感到气愤。

Answer 3

转()

它可能或不能做任何与您的(a)项不同的事情。价值是设定的。

友情链接