std::basic_string<CharT,Traits,Allocator>::substr
From cppreference.com
< cpp | string | basic string
(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. 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);.
Contents |
[edit] Parameters
pos | - | position of the first character to include |
count | - | length of the substring |
[edit] Return value
String containing the substring [
pos,
pos + count)
or [
pos,
size()
)
.
[edit] 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).
[edit] Complexity
Linear in count.
[edit] Notes
The allocator of the returned string is default-constructed: the new allocator might not be a copy of get_allocator()
.
[edit] 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)
[edit] Defect reports
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 |
[edit] See also
copies characters (public member function) | |
returns the number of characters (public member function) | |
finds the first occurrence of the given substring (public member function) | |
[static] |
special value. The exact meaning depends on the context (public static member constant) |
returns a substring (public member function of std::basic_string_view<CharT,Traits> )
|