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| (1) | ||
basic_string substr( size_type pos=0, size_type count= npos)const; | (until C++23) (constexpr since C++20) | |
constexpr basic_string substr( size_type pos=0, size_type count= npos)const&; | (since C++23) | |
constexpr basic_string substr( size_type pos=0, size_type count= npos)&&; | (2) | (since C++23) |
Returns a substring[pos, pos+ count). If the requested substring extends past the end of the string, i.e. thecount is greater thansize()- pos (e.g. ifcount== npos), the returned substring is[pos, size()).
Contents |
| pos | - | position of the first character to include |
| count | - | length of the substring |
String containing the substring[pos, pos+ count) or[pos, size()).
std::out_of_range ifpos> size().
If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee).
Linear incount.
The allocator of the returned string is default-constructed: the new allocator mightnot be a copy ofget_allocator().
#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, throwsstd::string sub5= a.substr(a.size()+3,50);std::cout<< sub5<<'\n';}catch(conststd::out_of_range& ex){std::cout<< ex.what()<<'\n';}}
Possible output:
abcdefghij567hijbasic_string::substr: __pos (which is 23) > this->size() (which is 20)
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 847 | C++98 | there was no exception safety guarantee | added strong exception safety guarantee |
| copies characters (public member function)[edit] | |
| returns the number of characters (public member function)[edit] | |
| finds the first occurrence of the given substring (public member function)[edit] | |
constexpr size_typenpos[static] | the special valuesize_type(-1), its exact meaning depends on the context[edit] |
| returns a substring (public member function of std::basic_string_view<CharT,Traits>)[edit] |
