Std :: string the capacity remains the same after deleting the elements, is it true while holding some memory?

Question

The following code snippet:

string a = "abc";
cout << a.capacity();
a.erase(a.begin() + 1, a.end());
cout << a.capacity();

... Outputs:

33

Even if I remove some elements from the row, the capacity will remain the same. So my questions are:

• Is any memory stored due to capacity? What if I don't explicitly reserve()'d?

• If I use reserve()and do not use the full capacity, am I losing memory?

• Should this extra memory (which I do not use) be allocated for something else, if necessary?

EDIT: Suppose y <

 string a= "something";
 a = "ab";

Now I know that athere will be no more than two characters. So is it wise to invoke reserve(2)so that memory is not wasted?

Answer 1

1) - - ? , () 'd?

, std::string - ¹ ( ) std::string. std::string ,

2) std:: reserve() ?

, , ; std::string , . , Short String Optimized std::string . .

3) , , - , ?

. std::string ² . .

EDIT: ,

string a= "something";

, . a.reserve(2) , ?

a , a.size(), , 2, ² .

, . std::string::reserve . . std::string::reserve(new_capacity_intended) new_capacity_intended , size() , , , std::string::shrink_to_fit.

( shrink_to_fit) :

string a= "something";
//resize it first
a.resize(2);  //or by some assignment such as a = "so";

//then
a.reserve(2); // or better still a.shrink_to_fit();

---

¹:

²: std::string::reserve std::string::shrink_to_fit .

Answer 2

:

• , . , . , .

• .

• 1): . . . .

string::reserve.

: , , . , , ( ). .

---

: reserve . reserve(n), , n. , reserve n n (. reserve ).

: reserve, . , . ( ++ 11, shrink_to_fit).

( ) gcc/clang, a 2. 100%, , :

auto a = string{"something"};
a = "ab";
cout << a << " " << a.capacity() << endl;
a.reserve(2);
cout << a << " " << a.capacity() << endl;

:

ab 9
ab 2