std::basic_string<CharT,Traits,Allocator>::substr
basic_string substr( size_type pos = 0, size_type count = npos ) const; |
(until C++20) | |
constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const; |
(since C++20) |
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()).
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().
Complexity
Linear in count.
Notes
The returned string is constructed as if by basic_string(data()+pos, count), which implies that the returned string's allocator will be default-constructed — the new allocator might not be a copy of this->get_allocator().
Example
#include <string>
#include <iostream>
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& e) {
std::cout << "pos exceeds string size\n";
}
}
Output:
abcdefghij 567 hij pos exceeds string size
See also
| copies characters (public member function) |
|
| returns the number of characters (public member function) |
|
| find characters in the string (public member function) |
|
|
[static]
|
special value. The exact meaning depends on the context (public static member constant) |
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