|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
void shrink_to_fit(); | (constexpr since C++20) | |
Requests the removal of unused capacity.
It is a non-binding request to reducecapacity() tosize(). It depends on the implementation if the request is fulfilled.
If (and only if) reallocation takes place, all pointers, references, and iterators are invalidated.
Contents |
Linear in the size of the string.
In libstdc++,shrink_to_fit() isnot available in C++98 mode.
#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 bytesDefault-constructed capacity is 15 and size 0Capacity after 42 appends is 240 and size 168Capacity after clear() is 240 and size 0Capacity after shrink_to_fit() is 15 and size 0 clang output (with -stdlib=libc++):Size of std::string is 24 bytesDefault-constructed capacity is 22 and size is 0Capacity after 42 appends is 191 and size is 168Capacity after clear() is 191 and size is 0Capacity after shrink_to_fit() is 22 and size is 0
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 operations | provided |
| LWG 2223 | C++98 | 1. references, pointers, and iterators were not invalidated 2. there was no complexity requirement | 1. they may be invalidated 2. required to be linear |
| returns the number of characters (public member function)[edit] | |
| returns the number of characters that can be held in currently allocated storage (public member function)[edit] | |
| changes the number of characters stored (public member function)[edit] |
