StringBuilder如何决定其容量应为多少？ [英] How does the StringBuilder decide how large its capacity should be?

问题描述

我知道，当sb已满时，当您使用sb.Append（..）时，StringBuilder对象会分配更多的内存。但是该容量增加了多少？

I know that the StringBuilder object allocates more memory when you use sb.Append(..) when the sb is already at capacity. But how much does that capacity increase?

    StringBuilder sb = new StringBuilder(5);
    sb.Append("0123456789");

现在sb的容量是什么，为什么？什么是乘数？

Now what is the capacity of sb and why? What is the multiplier?

为清楚起见。我问的是容量而不是长度。

Just for clarity. I am asking about capacity and not length.

谢谢！

推荐答案

除某些特殊情况外，每次容量都会翻倍：

The capacity doubles each time apart from some special cases:

• 如果加倍不够，那么容量会进一步增加到确切的数量是必需的。


• 有一个上限-0x7fffffff。

您可以看到该算法通过使用.NET Reflector或下载参考源。

You can see the algorithm by using .NET Reflector or downloading the reference source.

我无法发布官方.NET实现的源代码，但这是Mono实现的代码：

I can't post the source code for the official .NET implementation but here's the code for the Mono implementation:

// Try double buffer, if that doesn't work, set the length as capacity
if (size > capacity) {

    // The first time a string is appended, we just set _cached_str
    // and _str to it. This allows us to do some optimizations.
    // Below, we take this into account.
    if ((object) _cached_str == (object) _str && capacity < constDefaultCapacity)
        capacity = constDefaultCapacity;

    capacity = capacity << 1;  // This means "capacity *= 2;"

    if (size > capacity)
        capacity = size;

    if (capacity >= Int32.MaxValue || capacity < 0)
        capacity = Int32.MaxValue;

    if (capacity > _maxCapacity && size <= _maxCapacity)
        capacity = _maxCapacity;
}

我也建议您不要编写依赖于此特定代码的代码算法，因为它是实现细节，而不是接口所不能保证的。

I would also recommend that you don't write code that relies on this specific algorithm as it is an implementation detail, and not something that is guaranteed by the interface.

这篇关于StringBuilder如何决定其容量应为多少？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！