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std::basic_string::substr(3) C++ Standard Libary std::basic_string::substr(3) NAME std::basic_string::substr - std::basic_string::substr Synopsis basic_string substr( size_type pos = 0, size_type (until C++23) count = npos ) const; (const- expr since C++20) constexpr basic_string substr( size_type pos = 0, size_type count = (1) (since C++23) npos ) const&; constexpr basic_string substr( size_type pos = 0, (2) (since C++23) size_type count = npos ) &&; Returns a substring [pos, pos + count). If the requested substring extends past the end of the string, i.e. the count is greater than size() - pos (e.g. if count == npos), the returned substring is [pos, size()). 1) Equivalent to return basic_string(*this, pos, count);. 2) Equivalent to return basic_string(std::move(*this), pos, count);. Parameters pos - position of the first character to include count - length of the substring Return value String containing the substring [pos, pos + count) or [pos, size()). Exceptions std::out_of_range if pos > size(). If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee). Complexity Linear in count. Notes The allocator of the returned string is default-constructed: the new allocator might not be a copy of get_allocator(). Example // Run this code #include <iostream> #include <string> int main() { std::string a = "0123456789abcdefghij"; // count is npos, returns [pos, size()) std::string sub1 = a.substr(10); std::cout << sub1 << '\n'; // both pos and pos + count are within bounds, returns [pos, pos + count) std::string sub2 = a.substr(5, 3); std::cout << sub2 << '\n'; // pos is within bounds, pos + count is not, returns [pos, size()) std::string sub4 = a.substr(a.size() - 3, 50); // this is effectively equivalent to // std::string sub4 = a.substr(17, 3); // since a.size() == 20, pos == a.size() - 3 == 17, and a.size() - pos == 3 std::cout << sub4 << '\n'; try { // pos is out of bounds, throws std::string sub5 = a.substr(a.size() + 3, 50); std::cout << sub5 << '\n'; } catch (const std::out_of_range& ex) { std::cout << ex.what() << '\n'; } } Possible output: abcdefghij 567 hij basic_string::substr: __pos (which is 23) > this->size() (which is 20) Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 847 C++98 there was no exception safety added strong exception safety guarantee guarantee See also copy copies characters (public member function) size returns the number of characters length (public member function) find finds the first occurrence of the given substring (public member function) npos special value. The exact meaning depends on the context [static] (public static member constant) substr returns a substring (public member function of std::ba- sic_string_view<CharT,Traits>) http://cppreference.com 2024.06.10 std::basic_string::substr(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Complexity | Notes | Example | Possible output: | See also
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