Custom string class and add custom types to STL containers

13.44 compile a simplified version of the string class in the standard library and name it string. Your class should have at least one default constructor and one constructor that accepts the C-style string pointer parameters. Use allocator to allocate the required memory for your string class.

13.47 Add a copy constructor and a copy value assignment operator, and add a print statement. A message is printed every time the function is executed.

13.48 define a vector <string> and call push_back multiple times on it. Run the program and observe how many times the string has been copied.

#include<iostream>#include<string>#include<memory>#include<utility>#include<cstring>#include<vector>using namespace std;class String{public:    String()=default;    String(char *c);    String(const String&);    String& operator=(const String&);    string* begin() const { return elements;}    string* end() const { return first_free;}private:    static allocator<string> alloc;    string *elements;    string *first_free;};allocator<string> String::alloc;String::String(char *c){    size_t capacity=strlen(c);    auto data=alloc.allocate(capacity);    auto dest=data;    string s;    s.copy(c,strlen(c));    alloc.construct(dest++,s);    elements=data;    first_free=dest;}String::String(const String &s){    cout<<"copy construct"<<endl;    auto capacity=s.end()-s.begin();    auto data=alloc.allocate(capacity);    uninitialized_copy(s.begin(),s.end(),data);    elements=data;    first_free=data+capacity;}String& String::operator=(const String &s){    cout<<"copy = construct"<<endl;    auto capacity=s.end()-s.begin();    auto data=alloc.allocate(capacity);    uninitialized_copy(s.begin(),s.end(),data);    if(elements)    {        auto begin=elements;        auto end=first_free;        while(begin!=end)            alloc.destroy(begin++);        alloc.deallocate(elements,first_free-elements);    }    elements=data;    first_free=data+capacity;    return *this;}int main(){    vector<String> vec;    char ch[]="hello";    char ch1[]="world!";    cout<<vec.capacity()<<endl;     cout<<endl;    vec.push_back(String(ch));    cout<<vec.capacity()<<endl;    cout<<endl;    vec.push_back(String(ch1));    cout<<vec.capacity()<<endl;    cout<<endl;    vec.push_back(String(ch));    cout<<vec.capacity()<<endl;    cout<<endl;    vec.push_back(String(ch1));    cout<<vec.capacity()<<endl;    cout<<endl;    vec.push_back(String(ch1));    cout<<vec.capacity()<<endl;    cout<<endl;    vec.push_back(String(ch1));    cout<<vec.capacity()<<endl;    return 0;}

Running result:

Explanation: http://blog.csdn.net/HEYUTAO007/article/details/6702626

Custom string class and add custom types to STL containers