在C＃中，它是慢引用数组变量？ [英] In C#, Is it slower to reference an array variable?

问题描述

我有一个整数数组，而我通过他们的循环：

I've got an array of integers, and I'm looping through them:

for (int i = 0; i < data.Length; i++)
{
  // do a lot of stuff here using data[i]
}

如果我做的：

for (int i = 0; i < data.Length; i++)
{
  int value = data[i];
  // do a lot of stuff with value instead of data[i]
}

有任何性能收益/损失？

Is there any performance gain/loss?

这是我的理解，C / C ++数组元素直接访问，即整数n元素数组的长度为n * sizeof的（INT）一个连续的内存块，并且该程序访问元素我做的东西像*数据[I] = *数据[0] +（I *的sizeof（int）的）。 （请原谅我滥用的符号，但你明白我的意思。）

From my understanding, C/C++ array elements are accessed directly, i.e. an n-element array of integers has a contiguous memory block of length n * sizeof(int), and the program access element i by doing something like *data[i] = *data[0] + (i * sizeof(int)). (Please excuse my abuse of notation, but you get what I mean.)

因此​​，这意味着C / C ++应该没有业绩收益/损失引用数组变量。

So this means C/C++ should have no performance gain/loss for referencing array variables.

那么C＃？ C＃有一堆像data.Length，data.IsSynchronized，data.GetLowerBound（），data.GetEnumerator（）。

What about C#? C# has a bunch of extra overhead like data.Length, data.IsSynchronized, data.GetLowerBound(), data.GetEnumerator().

显然，一个C＃阵列是不一样的一个C / C ++数组

Clearly, a C# array is not the same as a C/C++ array.

那么，有什么评价呢？如果我存储int值=数据[i]和与价值的工作，或者是有没有性能影响？

So what's the verdict? Should I store int value = data[i] and work with value, or is there no performance impact?

推荐答案

是，还有一个性能损失，由于边界检查每个访问阵列。

Yes, there is a performance loss due to the bounds check for every access to the array.

否，您很可能并不需要担心。

No, you most likely don't need to worry about it.

是的，你可以应存储的价值，并与价值的工作。不，这不是因为性能问题，而是因为它使code更具有可读性（恕我直言）。

Yes, you can should store the value and work with the value. No, this isn't because of the performance issue, but rather because it makes the code more readable (IMHO).

顺便说一句，JIT编译器的也许的优化了多余的检查，所以它并不意味着你就会得到在每次调用检查。无论哪种方式，它可能不是值得你花时间担心;只是用它，如果它原来是一个瓶颈，你可以随时回去，并使用不安全块。

By the way, the JIT compiler might optimize out redundant checks, so it doesn't mean you'll actually get a check on every call. Either way, it's probably not worth your time to worry about it; just use it, and if it turns out to be a bottleneck you can always go back and use unsafe blocks.

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