当编译 StrVec 中的 reserve、resize、reallocate 函数时 gcc 报了如下错误？

[linux40]

more undefined references to `StrVec::alloc' follow，而且这三个函数当中只出现一个函数的定义的话，则无错误，下面贴代码：

	#ifndef STRVEC_H
	#define STRVEC_H
	#include <memory>
	#include <string>
	#include <utility>
	#include <initializer_list>
	class StrVec
	{
	public:
	StrVec():
	elements(nullptr), first_free(nullptr), cap(nullptr) {}
	StrVec(std::initializer_list<std::string> sl)
	{
	auto ptr_pair = alloc_n_copy(sl.begin(), sl.end());
	elements = ptr_pair.first;
	first_free = cap = ptr_pair.second;
	}
	StrVec(const StrVec &sv)
	{
	auto ptr_pair = alloc_n_copy(sv.begin(), sv.end());
	elements = ptr_pair.first;
	first_free = cap = ptr_pair.second;
	}
	StrVec &operator=(const StrVec &sv)
	{
	auto ptr_pair = alloc_n_copy(sv.begin(), sv.end());
	free();
	elements = ptr_pair.first;
	first_free = cap = ptr_pair.second;
	return *this;
	}
	~StrVec()
	{
	free();
	}
	void push_back(const std::string &s)
	{
	chk_n_alloc();
	alloc.construct(first_free++, s);
	}
	std::string *begin() const
	{
	return elements;
	}
	std::string *end() const
	{
	return first_free;
	}
	std::size_t size() const
	{
	return first_free - elements;
	}
	std::size_t capacity() const
	{
	return cap - elements;
	}
	void reserve(const std::size_t &sz);
	void resize(const std::size_t &sz, const std::string &s);
	private:
	static std::allocator<std::string> alloc;
	void chk_n_alloc()
	{
	if (first_free == cap)
	reallocate();
	}
	std::pair<std::string *, std::string *> alloc_n_copy
	(const std::string *b, const std::string *e)
	{
	auto new_elem = alloc.allocate(e - b);
	return {new_elem, std::uninitialized_copy(b, e, new_elem)};
	}
	void free();
	void reallocate();
	std::string *elements;
	std::string *first_free;
	std::string *cap;
	};
	#endif // STRVEC_H

view raw StrVec.h hosted with ❤ by GitHub

	#include "StrVec.h"
	void StrVec::reserve(const std::size_t &sz)
	{
	if (sz > capacity())
	{
	auto new_elem = alloc.allocate(sz);
	auto new_p = new_elem, p = elements;
	while (p != first_free)
	alloc.construct(new_p++, std::move(*p++));
	free();
	elements = new_elem;
	first_free = new_p;
	cap = new_elem + sz;
	}
	}
	void StrVec::resize(const std::size_t &sz, const std::string &s = "")
	{
	if (sz > capacity())
	{
	auto new_elem = alloc.allocate(sz * 2);
	auto new_p = new_elem, p = elements;
	while (p != first_free)
	alloc.construct(new_p++, std::move(*p++));
	std::uninitialized_fill_n(new_p, sz - size(), s);
	free();
	elements = new_elem;
	first_free = new_elem + sz;
	cap = new_elem + sz * 2;
	}
	else if (sz > size())
	{
	std::uninitialized_fill_n(first_free, sz - size(), s);
	first_free = elements + sz;
	}
	else
	{
	std::string *new_ff = elements + sz;
	for (auto p = new_ff; p != first_free; ++p)
	alloc.destroy(p);
	}
	}
	void StrVec::free()
	{
	if (elements)
	{
	for (auto p = elements; p != first_free; ++p)
	alloc.destroy(p);
	alloc.deallocate(elements, capacity());
	}
	}
	void StrVec::reallocate()
	{
	std::size_t new_cap = (elements == cap) ? 1 : 2 * size();
	auto new_elem = alloc.allocate(new_cap);
	auto new_p = new_elem, p = elements;
	while (p != first_free)
	alloc.construct(new_p++, std::move(*p++));
	free();
	elements = new_elem;
	first_free = new_p;
	cap = new_elem + new_cap;
	}

view raw wrong code hosted with ❤ by GitHub

第二个是StrVec.cc
顺便求吐槽其他可以改进或改正的地方。

手机端看不了代码啊。。。

呃，能看

问题解决了