capacity | 易学教程

StringBuilder capacity()

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问题 I noticed that the capacity method returns StringBuilder capacity without a logic way ... sometime its value is equals to the string length other time it's greater... is there an equation for know which is its logic? 回答1: When you append to the StringBuilder , the following logic happens: if (newCount > value.length) { expandCapacity(newCount); } where newCount is the number of characters needed, and value.length is the current size of the buffer. expandCapacity simply increases the size of

std::vector capacity after copying

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问题 Does vector::operator= change vector capacity? If so, how? Does vector's copy constructor copy capacity? I looked through documentation but could not find a specific answer. Is it implementation dependent? 回答1: All you're guaranteed is that: The vector has enough capacity to store its elements. (Obviously.) The vector won't get a new capacity until it's current capacity is full.* So how much extra or little an implementation wants to put is up to the implementation. I think most will make

Does clearing a vector affect its capacity?

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问题 I instantiate an std::vector foo(1000) . foo.size() is now 1000 and foo.capacity() is also 1000. If I clear the vector with foo.clear() , the size() is now 0, but what is the capacity() ? Does the standard say anything about that? 回答1: No, it doesn't. The capacity of a vector never decreases. That isn't mandated by the standard but it's so both in standard library implementations of VC++ and g++. In order to set the capacity just enough to fit the size, use the famous swap trick vector<T>()

Why start an ArrayList with an initial capacity?

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The usual constructor of ArrayList is: ArrayList<?> list = new ArrayList<>(); But there is also an overloaded constructor with a parameter for its initial capacity: ArrayList<?> list = new ArrayList<>(20); Why is it useful to create an ArrayList with an initial capacity when we can append to it as we please? If you know in advance what the size of the ArrayList is going to be, it is more efficient to specify the initial capacity. If you don't do this, the internal array will have to be repeatedly reallocated as the list grows. The larger the final list, the more time you save by avoiding the

Calculating usage of localStorage space

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问题 I am creating an app using the Bespin editor and HTML5\'s localStorage. It stores all files locally and helps with grammar, uses JSLint and some other parsers for CSS and HTML to aid the user. I want to calculate how much of the localStorage limit has been used and how much there actually is. Is this possible today? I was thinking for not to simply calculate the bits that are stored. But then again I\'m not sure what more is there that I can\'t measure myself. 回答1: You may be able to get an

Why start an ArrayList with an initial capacity?

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问题 The usual constructor of ArrayList is: ArrayList<?> list = new ArrayList<>(); But there is also an overloaded constructor with a parameter for its initial capacity: ArrayList<?> list = new ArrayList<>(20); Why is it useful to create an ArrayList with an initial capacity when we can append to it as we please? 回答1: If you know in advance what the size of the ArrayList is going to be, it is more efficient to specify the initial capacity. If you don't do this, the internal array will have to be