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std::basic_...ng::capacity(3) C++ Standard Libarystd::basic_...ng::capacity(3) NAME std::basic_string::capacity - std::basic_string::capacity Synopsis size_type capacity() const; (until C++11) size_type capacity() const noexcept; (since C++11) (until C++20) constexpr size_type capacity() const noexcept; (since C++20) Returns the number of characters that the string has currently allo- cated space for. Parameters (none) Return value Capacity of the currently allocated storage, i.e. the storage avail- able for storing elements. Complexity Constant Notes Memory locations obtained from the allocator but not available for storing any element are not counted in the allocated storage. Note that the null terminator is not an element of the std::basic_string. Example // Run this code #include <iostream> #include <iomanip> #include <string> void show_capacity(std::string const& s) { std::cout << std::quoted(s) << " has capacity " << s.capacity() << ".\n"; } int main() { std::string s{"Exemplar"}; show_capacity(s); s += " is an example string."; show_capacity(s); s.clear(); show_capacity(s); std::cout << "\nDemonstrate the capacity's growth policy." "\nSize: Capacity: Ratio:\n" << std::left; std::string g; auto old_cap {g.capacity()}; for(int mark{}; mark != 5; ++mark) { while (old_cap == g.capacity()) g.push_back('.'); std::cout << std::setw( 7) << g.size() << std::setw(11) << g.capacity() << std::setw(10) << g.capacity() / sta- tic_cast<float>(old_cap) << '\n'; old_cap = g.capacity(); } } Possible output: "Exemplar" has capacity 15. "Exemplar is an example string." has capacity 30. "" has capacity 30. Demonstrate the capacity's growth policy. Size: Capacity: Ratio: 16 30 2 31 60 2 61 120 2 121 240 2 241 480 2 See also size returns the number of characters length (public member function) reserve reserves storage (public member function) http://cppreference.com 2022.07.31 std::basic_...ng::capacity(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Example | Possible output: | See also
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