std::basic_string::shrink_to_fit(3)

NAME
std::basic_string::shrink_to_fit - std::basic_string::shrink_to_fit

Synopsis
   void shrink_to_fit(); (constexpr since C++20)
   Requests the removal of unused capacity.
   It is a non-binding request to reduce capacity() to size(). It depends on the
   implementation if the request is fulfilled.
   If (and only if) reallocation takes place, all pointers, references, and iterators
   are invalidated.

Parameters
   (none)

Return value
   (none)

Complexity
   (unspecified) (until C++17)
   Linear in the size of the string. (since C++17)

Notes
   In libstdc++, shrink_to_fit() is not available in C++98 mode.

Example
// Run this code
 #include <iostream>
 #include <string>
 int main()
 {
     std::string s;
     std::cout << "Size of std::string is " << sizeof s << " bytes\n"
         << "Default-constructed capacity is " << s.capacity()
         << " and size is " << s.size() << '\n';
     for (int i = 0; i < 42; i++)
         s.append(" 42 ");
     std::cout << "Capacity after 42 appends is " << s.capacity()
         << " and size is " << s.size() << '\n';
     s.clear();
     std::cout << "Capacity after clear() is " << s.capacity()
         << " and size is " << s.size() << '\n';
     s.shrink_to_fit();
     std::cout << "Capacity after shrink_to_fit() is " << s.capacity()
         << " and size is " << s.size() << '\n';
 }

Possible output:
 GCC output:
 Size of std::string is 32 bytes
 Default-constructed capacity is 15 and size 0
 Capacity after 42 appends is 240 and size 168
 Capacity after clear() is 240 and size 0
 Capacity after shrink_to_fit() is 15 and size 0
 clang output (with -stdlib=libc++):
 Size of std::string is 24 bytes
 Default-constructed capacity is 22 and size is 0
 Capacity after 42 appends is 191 and size is 168
 Capacity after clear() is 191 and size is 0
 Capacity after shrink_to_fit() is 22 and size is 0
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
   LWG 755 C++98 std::string lacked explicit shrink-to-fit provided
                      operations

See also
   size returns the number of characters
   length (public member function)
            returns the number of characters that can be held in currently allocated
   capacity storage
            (public member function)
   resize changes the number of characters stored
            (public member function)