c 2b 2b substring

1s.substr(pos,len);

1// string::substr
2#include <iostream>
3#include <string>
4
5int main ()
6{
7  std::string str="We think in generalities, but we live in details.";
8                                           // (quoting Alfred N. Whitehead)
9
10  std::string str2 = str.substr (3,5);     // "think"
11
12  std::size_t pos = str.find("live");      // position of "live" in str
13
14  std::string str3 = str.substr (pos);     // get from "live" to the end
15
16  std::cout << str2 << ' ' << str3 << '\n';
17
18  return 0;
19}

1#include <string>
2#include <iostream>
3 
4int main()
5{
6    std::string a = "0123456789abcdefghij";
7 
8    // count is npos, returns [pos, size())
9    std::string sub1 = a.substr(10);
10    std::cout << sub1 << '\n';
11 
12    // both pos and pos+count are within bounds, returns [pos, pos+count)
13    std::string sub2 = a.substr(5, 3);
14    std::cout << sub2 << '\n';
15 
16    // pos is within bounds, pos+count is not, returns [pos, size()) 
17    std::string sub4 = a.substr(a.size()-3, 50);
18    // this is effectively equivalent to
19    // std::string sub4 = a.substr(17, 3);
20    // since a.size() == 20, pos == a.size()-3 == 17, and a.size()-pos == 3
21 
22    std::cout << sub4 << '\n';
23 
24    try {
25        // pos is out of bounds, throws
26        std::string sub5 = a.substr(a.size()+3, 50);
27        std::cout << sub5 << '\n';
28    } catch(const std::out_of_range& e) {
29        std::cout << "pos exceeds string size\n";
30    }
31}

1string sub_string=main_string.substr(first_pos_of_the_substring_from_main_string,length_of_the_substring_from_main_string_starting_from_the_first_position