c++ - string::insert produces a runtime error -

i have string b, want reverse it, append result string a. tried gives me runtime error

a.insert(a.end(), b.rbegin(), b.rend()) 

which is

terminate called after throwing instance of 'std::length_error'   what():  basic_string::_m_create 

what's problem line of code ?

update : here short program throws same exception :

#include <iostream> #include <string>   using namespace std;       int main (int argc, const char* argv[]) {         string result="bbb";         string tail="aaa";         result.insert(result.end(), tail.rend(), tail.rbegin());         cout << result << endl;         return 0;      } 

i using gcc 5.4.0 on ubuntu 16.0.4

the "insert" you're using doesn't work because:

inserts characters range [first, last) before element pointed pos. overload not participate in overload resolution if inputit not satisfy inputiterator. (since c++11)

the begin() of can't valid pos. case, can use append instead:

a.append(b.rbegin(), b.rend());