在循环中声明变量是否有任何开销?(C++)

2021-12-08 00:00:00 loops c++ variable-declaration

我只是想知道如果你做这样的事情是否会降低速度或效率:

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++;
}

声明 int var 一百次.在我看来好像会有，但我不确定.这样做会更实用/更快吗:

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++;
}

或者它们在速度和效率方面是否相同?

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

推荐答案

局部变量的栈空间通常在函数作用域内分配.所以循环内部不会发生堆栈指针调整，只是将 4 分配给 var.因此，这两个代码段具有相同的开销.

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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