std::generate not working on an std::vector

Question

#include <iostream>
#include <random>
#include <algorithm>

int main()
{
  std::mt19937 mt;
  std::uniform_int_distribution<int> d(0, 255);
  int l = 500;
  std::vector<int> k(l);
  std::generate(k.begin(), k.end(), d(mt));
  return(0);
}

trying to compile with both g++ 4.7.2 and g++ 4.8.1 like so

g++ -std=c++11 main.cpp

the reported error is

In file included from /usr/include/c++/4.7/algorithm:63:0,
                 from main.cpp:3:
/usr/include/c++/4.7/bits/stl_algo.h: In instantiation of ‘void std::generate(_FIter, _FIter, _Generator) [with _FIter = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; _Generator = int]’:
main.cpp:11:42:   required from here
/usr/include/c++/4.7/bits/stl_algo.h:5083:2: error: ‘__gen’ cannot be used as a function

I don't have any clue or idea about what can be possibly wrong in this case.

Answer 1

std::generate takes a function object and applies its return value to the sequence container. But std::uniform_int_distribution<T>::operator () doesn't return a function object, it actually generates the random value and returns it. If you want to pass a functor, use a lambda:

std::generate(k.begin(), k.end(), [&] { return d(mt); });
//                                ^^^^^^^^^^^^^^^^^^^^^

Here is a working example of your program.