【足迹C++primer】47、Moving Objects(2)

Moving Objects(2)

Rvalue References and Member Functions

StrVec.h

#ifndef STRVEC_H#define STRVEC_H#include <iostream>#include <memory>#include <utility>// simplified implementation of the memory allocation strategy for a vector-like classclass StrVec {public:// copy control members    StrVec():  elements(0), first_free(0), cap(0) { }StrVec(const StrVec&);            // copy constructorStrVec &operator=(const StrVec&); // copy assignment~StrVec();                            // destructor// additional constructorStrVec(const std::string*, const std::string*);    void push_back(const std::string&);  // copy the element    void push_back(std::string&&);       //move the element// add elements    size_t size() const { return first_free - elements; }    size_t capacity() const { return cap - elements; }// iterator interfacestd::string *begin() const { return elements; }std::string *end() const { return first_free; }// operator functions covered in chapter 14std::string& operator[](std::size_t n){ return elements[n]; }const std::string& operator[](std::size_t n) const{ return elements[n]; }private:    static std::allocator<std::string> alloc; // allocates the elements// utility functions://  used by members that add elements to the StrVecvoid chk_n_alloc(){ if (size() == capacity()) reallocate(); }    // used by the copy constructor, assignment operator, and destructorstd::pair<std::string*, std::string*> alloc_n_copy    (const std::string*, const std::string*);void free();             // destroy the elements and free the space    void reallocate();       // get more space and copy the existing elements    std::string *elements;   // pointer to the first element in the array    std::string *first_free; // pointer to the first free element in the array    std::string *cap;        // pointer to one past the end of the array};#include <algorithm>inlineStrVec::~StrVec() { free(); }inlinestd::pair<std::string*, std::string*>StrVec::alloc_n_copy(const std::string *b, const std::string *e){// allocate space to hold as many elements as are in the rangestd::string *data = alloc.allocate(e - b);// initialize and return a pair constructed from data and// the value returned by uninitialized_copyreturn std::make_pair(data, uninitialized_copy(b, e, data));}inlineStrVec::StrVec(const StrVec &s){// call alloc_n_copy to allocate exactly as many elements as in sstd::pair<std::string*, std::string*> newdata =alloc_n_copy(s.begin(), s.end());elements = newdata.first;first_free = cap = newdata.second;}inlinevoid StrVec::free(){    // may not pass deallocate a 0 pointer; if elements is 0, there's no work to doif (elements) {    // destroy the old elements in reverse orderfor (std::string *p = first_free; p != elements; /* empty */)alloc.destroy(--p);alloc.deallocate(elements, cap - elements);}}inlineStrVec &StrVec::operator=(const StrVec &rhs){// call alloc_n_copy to allocate exactly as many elements as in rhsstd::pair<std::string*, std::string*> data =alloc_n_copy(rhs.begin(), rhs.end());free();elements = data.first;first_free = cap = data.second;return *this;}inlinevoid StrVec::reallocate(){    // we'll allocate space for twice as many elements as the current size    size_t newcapacity = size() ? 2 * size() : 1;// allocate new memorystd::string *newdata = alloc.allocate(newcapacity);// copy the data from the old memory to the newstd::string *dest = newdata;  // points to the next free position in the new array    std::string *elem = elements; // points to the next element in the old arrayfor (size_t i = 0; i != size(); ++i)alloc.construct(dest++, *elem++);free();  // free the old space once we've moved the elements    // update our data structure to point to the new elements    elements = newdata;    first_free = dest;    cap = elements + newcapacity;}inlineStrVec::StrVec(const std::string *b, const std::string *e){// call alloc_n_copy to allocate exactly as many elements as in ilstd::pair<std::string*, std::string*> newdata = alloc_n_copy(b, e);elements = newdata.first;first_free = cap = newdata.second;}#endif

StrVec.cc

#include "StrVec.h"#include <string>#include <utility>// errata fixed in second printing -- // StrVec's allocator should be a static member not an ordinary member// definition for static data memberstd::allocator<std::string> StrVec::alloc;  // all other StrVec members are inline and defined inside StrVec.h

inlinevoid StrVec::push_back(const string& s){    chk_n_alloc(); // ensure that there is room for another element    // construct a copy of s in the element to which first_free points    alloc.construct(first_free++, s);}inlinevoid StrVec::push_back(string&& s){    chk_n_alloc();    alloc.construct(first_free++, std::move(s));}void fun1(){    StrVec vec;    string s="my name is cutter_point!";    vec.push_back(s);   //调用const string&这个    vec.push_back("China!");    //调用string&&}

class Foo{public:    Foo()=default;    Foo(const Foo&);    //copy构造函数    Foo &operator=(const Foo&) &;   //返回一个左值&&表示返回右值//    Foo someMem() & const;          //错误，const应放第一位    Foo anotherMem() const &;       //正确};Foo &Foo::operator=(const Foo &rhs) &{    return *this;}Foo::Foo(const Foo &f){}void fun2(){    Foo &retFoo();  //返回一个引用，是一个左值    Foo retVal();      //返回一个值，右值调用    Foo i, j;       //i,j是左值    i=j;            //i是左值//    retFoo()=j;     //OK这个返回的是一个左值//    retVal()=j;     //错误。retVal是一个右值}

Overloading and Reference Functions

class Foo{public:    Foo()=default;//    Foo(const Foo&);    //copy构造函数//    Foo(Foo&&);    Foo &operator=(const Foo&) &;   //返回一个左值&&表示返回右值//    Foo someMem() & const;          //错误，const应放第一位    Foo anotherMem() const &;       //正确    Foo sorted() &&;        //返回右值    Foo sorted() const &;   //返回左值private:    vector<int> data;};Foo Foo::sorted() &&{    sort(data.begin(), data.end());    return *this;}Foo Foo::sorted() const &{    Foo ret(*this);    sort(ret.data.begin(), ret.data.end());    return ret;}

int main(){    string s1="a value", s2="this is a pig.";    auto n=(s1+s2).find('e');    cout<<n<<endl;    return 0;}

PS:现在的感觉是很不爽，不知道学这玩意什么时候才能去找工作，不知道去那好，还是耐心点，耐着性子，只要默默地向自己的目标前进就好，未来有我的机遇等着我，我现在要做的就是在机遇来的时候我可以狠狠的抓住！！！以免后悔一生