在类外部定义类成员记得加类作用域！切记

  1 #include<iostream>
  2 #include<algorithm>
  3 #include<memory>//the hearder file of shared_ptr
  4 #include <vector>
  5 #include <list>
  6 #include <map>
  7 #include <string>
  8 #include <set>
  9 #include <utility>
 10 
 11 using namespace std;
 12 
 13 
 14 class StrVec {
 15 public:
 16     StrVec() ://allocator成员进行默认初始化
 17         elements(0), first_free(0), cap(0) {}
 18     StrVec(const StrVec&);
 19     StrVec& operator=(const StrVec&);
 20     ~StrVec();
 21 
 22     void push_back(const std::string&);
 23     size_t size()const { return first_free - elements; }
 24     size_t capacity()const { return cap - elements; }
 25     std::string *begin()const { return elements; }
 26     std::string *end()const { return first_free; }
 27 private:
 28     static std::allocator<std::string> alloc;
 29     void chk_n_alloc() {
 30         if (size() == capacity())reallocate();
 31     }
 32     std::pair<std::string*, std::string*> alloc_n_copy(const std::string*, const std::string*);
 33     void free();
 34     void reallocate();
 35 
 36     std::string *elements;
 37     std::string *first_free;
 38     std::string *cap;
 39 };
 40 
 41 allocator<string> StrVec::alloc;
 42 
 43 void StrVec::push_back(const string& s) {
 44     chk_n_alloc();//检查是否有可用空间
 45     alloc.construct(first_free++, s);
 46 }
 47 
 48 pair<string*, string*> StrVec::alloc_n_copy(const string*b, const string*e) {
 49     string* newdata = alloc.allocate(e - b);
 50     return make_pair(newdata, uninitialized_copy(b, e, newdata));
 51 }
 52 
 53 void StrVec::free() {//销毁元素并且释放内存
 54     if (elements) {//检查所要释放的内存非空
 55         for (string* p = first_free;p != elements;/*空哦*/)
 56             alloc.destroy(--p);//逆序销毁
 57         alloc.deallocate(elements, cap - elements);
 58     }
 59 }
 60 
 61 StrVec::StrVec(const StrVec& v) {
 62     auto newdata = alloc_n_copy(v.begin(), v.end());
 63     elements = newdata.first;
 64     cap = first_free = newdata.second;
 65 }
 66 
 67 StrVec& StrVec::operator=(const StrVec& v) {
 68     auto newdata = alloc_n_copy(v.begin(), v.end());
 69 
 70     free();
 71     elements = newdata.first;
 72     cap = first_free = newdata.second;
 73     return *this;
 74 }
 75 
 76 StrVec::~StrVec() { free(); }
 77 
 78 void StrVec::reallocate() {
 79     auto newcapacity = size() ? size() * 2 : 1;
 80 
 81     auto newdata = alloc.allocate(newcapacity);
 82     auto dest = newdata;
 83     auto ele = elements;//elements不可改变，下面size()和free()都将用到
 84 
 85     for (size_t i = 0;i != size();i++)
 86         alloc.construct(dest++, *ele++);
 87     free();
 88 
 89     elements = newdata;
 90     first_free = dest;
 91     cap = elements + newcapacity;
 92 }
 93 
 94 int main(void) {
 95     StrVec xi;
 96     for (int i = 0;i < 10;i++)xi.push_back("xixi");
 97     for (const auto& mem : xi)cout << mem << " ";
 98 
 99     cout << endl;
100     return 0;
101 }
静态成员alloc前面没加StrVec::导致报错，无法解析的外部命令，大概长这个样子：
想起来以前也碰到过，那时候没弄清楚，只是把成员函数的实现拉进类内了，受教（抱拳