From cppreference.com
size_typemax_size()constnoexcept;(since C++23)Returns the maximum number of elements the container is able to hold due to system or library implementation limitations. Equivalent to std::min<size_type>(c.keys.max_size(),c.values.max_size()).
Return value
Maximum number of elements.
Complexity
Constant.
Notes
This value typically reflects the theoretical limit on the size of the container, at most std::numeric_limits<difference_type>::max(). At runtime, the size of the container may be limited to a value smaller than max_size() by the amount of RAM available.
Example
Run this code
#include<iostream>#include<flat_map>#include<locale>intmain(){std::flat_multimap<char,char>q;std::cout.imbue(std::locale("en_US.UTF-8"));std::cout<<"Maximum size of a std::flat_multimap is "<<q.max_size()<<'\n';}Possible output:
Maximum size of a std::flat_multimap is 9,223,372,036,854,775,807 See also
returns the number of elements
(public member function)