std::basic_string<CharT,Traits,Allocator>::substr (3) - Linux Man Pages

std::basic_string<CharT,Traits,Allocator>::substr: std::basic_string<CharT,Traits,Allocator>::substr


std::basic_string<CharT,Traits,Allocator>::substr - std::basic_string<CharT,Traits,Allocator>::substr


basic_string substr( size_type pos = 0,
size_type count = npos ) const;

Returns a substring [pos, pos+count). If the requested substring extends past the end of the string, or if count == npos, the returned substring is [pos,size()).


pos - position of the first character to include
count - length of the substring

Return value

String containing the substring [pos, pos+count).


std::out_of_range if pos >size()


Linear in count


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 will not be a copy of this->get_allocator().


// Run this code

  #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);
      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";


  pos exceeds string size

See also

       copies characters
copy (public member function)
       returns the number of characters
size (public member function)
       find characters in the string
find (public member function)