#ifndef STRVEC_H#define STRVEC_H#include<iostream>#include<string>#include<utility>#include<memory>using namespace std;class StrVec{public:    StrVec():elements(nullptr),first_free(nullptr),cap(nullptr){}    StrVec(const StrVec&);    StrVec& operator=(const StrVec&);    ~StrVec();    void push_back(const string&);    size_t size() const { return first_free-elements;}    size_t capacity() const { return cap-elements;}    string *begin() const  { return elements;}    string *end() const { return first_free;}    void reserve(size_t n);    void resize(size_t n,string s=string());    StrVec(initializer_list<string> il)    {        auto newcapacity=il.size();        auto newdata=alloc.allocate(newcapacity);        auto dest=newdata;        auto elem=il.begin();        while(elem!=il.end())            alloc.construct(dest++,*elem);        elements=newdata;        first_free=cap=dest;    }private:    static allocator<string> alloc;    string *elements;    string *first_free;    string *cap;    void chk_n_alloc()    {        if(size()==capacity()) reallocate();    }    pair<string*,string*> alloc_n_copy(const string*,const string*);    void free();    void reallocate();};#endif // STRVEC_H

#include"StrVec.h"allocator<string> StrVec::alloc;StrVec::StrVec(const StrVec &s){    auto newdata=alloc_n_copy(s.begin(),s.end());    elements=newdata.first;    first_free=newdata.second;    cap=newdata.second;}StrVec& StrVec::operator=(const StrVec &s){    auto data=alloc_n_copy(s.begin(),s.end());    free();    elements=data.first;    first_free=cap=data.second;    return *this;}StrVec::~StrVec(){    free();}void StrVec::push_back(const string &s){    chk_n_alloc();    alloc.construct(first_free++,s);}pair<string*,string*> StrVec::alloc_n_copy(const string *b, const string *e){    auto data=alloc.allocate(e-b);    return {data,uninitialized_copy(b,e,data)};}void StrVec::free(){    if(elements)    {
　　　　 //for_each(&first_free,&elements,[](string *p) { alloc.destroy(p);}); lambda式子        for(auto p=first_free;p!=elements;)            alloc.destroy(--p);        alloc.deallocate(elements,cap-elements);    }}void StrVec::reallocate(){    auto newcapacity=size()?2*size():1;    auto newdata=alloc.allocate(newcapacity);    auto dest=newdata;    auto elem=elements;    for(size_t i=0;i!=size();++i)        alloc.construct(dest++,std::move(*elem++));    elements=newdata;    first_free=dest;    cap=elements+newcapacity;}void StrVec::reserve(size_t n){    if(capacity()<n)        reallocate();}void StrVec::resize(size_t n,string s){    if(size()<n)        push_back(s);    else if(size()>n)    {        for(auto p=elements+n;p!=first_free;)            alloc.destroy(p++);        first_free=elements+n;    }}