如何使用glibc的字符串实现在堆栈上分配std :: string? [英] How do I allocate a std::string on the stack using glibc's string implementation?
问题描述
int main(void)
{
std::string foo("foo");
}
我的理解是，上面的代码使用默认的分配器来调用new.因此，即使std :: string foo分配在堆栈上，foo内部的内部缓冲区也分配在堆上.
My understanding is that the above code uses the default allocator to call new. So even though the std::string foo is allocated on the stack the internal buffer inside of foo is allocated on the heap.
如何创建一个完全在堆栈上分配的字符串?
How can I create a string that is allocated entirely on the stack?
推荐答案
我最近想自己做一下，发现下面的代码可以说明问题:
I wanted to do just this myself recently and found the following code illuminating:
它定义了一个新的std::allocator，它可以为基于STL容器的存储的初始分配提供基于堆栈的分配.我最终想找到一种解决我特定问题的方法，所以我实际上并未亲自使用该代码，但也许对您有用.请务必阅读代码中有关用法和注意事项的注释.
It defines a new std::allocator which can provide stack-based allocation for the initial allocation of storage for STL containers. I wound up finding a different way to solve my particular problem, so I didn't actually use the code myself, but perhaps it will be useful to you. Do be sure to read the comments in the code regarding usage and caveats.
对于那些质疑这样做的实用性和合理性的人，请考虑:
To those who have questioned the utility and sanity of doing this, consider:
- 通常您会先验地知道您的字符串具有合理的最大大小.例如，如果字符串将存储一个十进制格式的32位整数，则您知道不需要多于11个字符.在这种情况下，不需要可以动态增长为无限大小的字符串.
- 在许多情况下，从堆栈分配比从堆分配更快.
- 如果频繁创建和销毁字符串(假设它是常用的实用程序函数中的局部变量)，则从堆栈而不是堆进行分配将避免在堆分配器中产生碎片.对于使用大量内存的应用程序，这可能会改变游戏规则.
有人评论说，使用基于堆栈的分配的字符串将不是std::string，就好像这在某种程度上削弱了它的效用.的确，您不能将两者互换使用，因此您将无法将stackstring传递给需要std::string的函数.但是(如果操作正确)，您将可以在stackstring上使用现在在std::string上使用的所有相同成员函数，例如find_first_of()，append()等.begin()和end()仍然可以正常工作，因此您将能够使用许多STL算法.当然，从最严格的意义上讲，它不是std::string，但从实际意义上讲，它仍然是字符串"，并且仍然会非常有用.
Some people have commented that a string that uses stack-based allocation will not be a std::string as if this somehow diminishes its utility. True, you can't use the two interchangeably, so you won't be able to pass your stackstring to functions expecting a std::string. But (if you do it right), you will be able to use all the same member functions on your stackstring that you use now on std::string, like find_first_of(), append(), etc. begin() and end() will still work fine, so you'll be able to use many of the STL algorithms. Sure, it won't be std::string in the strictest sense, but it will still be a "string" in the practical sense, and it will still be quite useful.
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