重載運算符 ==和!=的重載 問題:假如有一個類似於vector的類,這個類只能存放string,當有2個這個類的對象時,如何比較這2個對象。 自己重載==和!= 代碼(重載==,!=) c++ include include include class string_vector{ friend ...
重載運算符 ==和!=的重載
問題:假如有一個類似於vector的類,這個類只能存放string,當有2個這個類的對象時,如何比較這2個對象。
自己重載==和!=
代碼(重載==,!=)
#include <iostream>
#include <memory>
#include <string>
class string_vector{
friend bool operator==(const string_vector&, const string_vector&);
friend bool operator!=(const string_vector&, const string_vector&);
public:
string_vector():
elements(nullptr), first_free(nullptr), cap(nullptr){}
string_vector(const string_vector&);
string_vector& operator=(const string_vector&);
string_vector(std::initializer_list<std::string>);
~string_vector();
void push_back(const std::string&);
size_t size() const {
return first_free - elements;
};
size_t capacity() const {
return cap - elements;
}
void resize(size_t, std::string&);
void resize(size_t);
void reserve(size_t);
std::string* begin() const{return elements;}
std::string* end() const{return first_free;}
private:
static std::allocator<std::string> alloc;
//static const int a = 10;
void chk_n_alloc(){
if(size() == capacity())
reallocate();
}
std::pair<std::string*, std::string*> alloc_n_copy
(const std::string* b, const std::string* e);
void free();
void reallocate();
void reallocate(size_t);
std::string* elements;//指向第一個元素的指針
std::string* first_free;//指向最後一個元素的下一個位置的指針
std::string* cap;//指向vector空間最後一個位置的下一個位置的指針
};
//必須在類的外面再定義一次,否則後面使用alloc的地方,編譯不過
std::allocator<std::string> string_vector::alloc;
std::pair<std::string*, std::string*> string_vector::alloc_n_copy
(const std::string* b, const std::string* e){
auto data = alloc.allocate(e - b);
return {data, std::uninitialized_copy(b, e, data)};
}
void string_vector::push_back(const std::string& s){
chk_n_alloc();
alloc.construct(first_free++, s);
}
void string_vector::free(){
if(elements){
for(auto p = first_free; p != elements;)
alloc.destroy(--p);
alloc.deallocate(elements, cap - elements);
}
}
string_vector::string_vector(const string_vector& s){
auto newdata = alloc_n_copy(s.begin(), s.end());
elements = newdata.first;
first_free = cap = newdata.second;
}
string_vector::string_vector(std::initializer_list<std::string> sl){
auto newdata = alloc_n_copy(sl.begin(), sl.end());
elements = newdata.first;
first_free = cap = newdata.second;
}
string_vector::~string_vector(){
free();
}
string_vector& string_vector::operator=(const string_vector& rhs){
auto newdata = alloc_n_copy(rhs.begin(), rhs.end());
free();
elements = newdata.first;
first_free = cap = newdata.second;
return *this;
}
void string_vector::reallocate(){
auto newcap = size() ? size() * 2 : 1;
auto newdata = alloc.allocate(newcap);
auto dest = newdata;
auto elem = elements;
for(size_t i = 0; i != size(); ++i){
alloc.construct(dest++, std::move(*elem++));
}
free();
elements = newdata;
first_free = dest;
cap = elements + newcap;
}
void string_vector::reallocate(size_t sz){
auto newcap = sz * 2;
auto newdata = alloc.allocate(newcap);
auto dest = newdata;
auto elem = elements;
for(size_t i = 0; i != size(); ++i){
alloc.construct(dest++, std::move(*elem++));
}
free();
elements = newdata;
first_free = dest;
cap = elements + newcap;
}
void string_vector::reserve(size_t sz){
if(sz > capacity()){
reallocate(sz);
}
}
void string_vector::resize(size_t sz){
size_t cap = capacity();
if(sz > cap){
reallocate(sz);
for(size_t i = size();i != sz; ++i){
//調用string的預設構造方法
alloc.construct(first_free++);
}
}
else if(sz < size()){
for(size_t i = sz;i != size(); ++i){
//調用string的西溝函數
alloc.destroy(--first_free);
}
}
}
void string_vector::resize(size_t sz, std::string& s){
size_t cap = capacity();
if(sz > cap){
reallocate(sz);
for(size_t i = size();i != sz; ++i){
//調用string的非預設構造方法
alloc.construct(first_free++, s);
}
}
else if(sz < size()){
for(size_t i = sz;i != size(); ++i){
//調用string的西溝函數
alloc.destroy(--first_free);
}
}
}
bool operator==(const string_vector& lhs, const string_vector& rhs){
if(lhs.size() == rhs.size()){
auto *p1 = lhs.elements;
auto *p2 = rhs.elements;
while(p1 != lhs.first_free){
if(*p1++ != *p2++){
return false;
}
}
return true;
}else{
return false;
}
}
bool operator!=(const string_vector& lhs, const string_vector& rhs){
return !operator==(lhs, rhs);
}
int main(){
string_vector sv1{"112"};
string_vector sv2{"11"};
if(sv1 != sv2){
std::cout << "!=" << std::endl;
}
else{
std::cout << "==" << std::endl;
}
}