在循环中声明变量是否有开销？ （C ++）

问题描述

我只是想知道如果你这样做会有任何的速度或效率的损失：

I am just wondering if there would be any loss of speed or efficiency if you did something like this:

int i = 0;
while(i < 100)
{
    int var = 4;
    i++;
}

它声明 int var 一百次。在我看来，似乎会有，但我不知道。这将是更实际/更快的做到这一点：

which declares int var one hundred times. It seems to me like there would be, but I'm not sure. would it be more practical/faster to do this instead:

int i = 0;
int var;
while(i < 100)
{
    var = 4;
    i++;
}

或者他们是相同的，速度和效率吗？

or are they the same, speedwise and efficiency-wise?

推荐答案

局部变量的堆栈空间通常在函数范围内分配。因此，在循环中不会发生堆栈指针调整，只需将4赋值给 var 。因此，这两个片段具有相同的开销。

Stack space for local variables is usually allocated in function scope. So no stack pointer adjustment happens inside the loop, just assigning 4 to var. Therefore these two snippets have the same overhead.

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