c++ - Generate matrix with std::generate -

using reference. behavior of std::generate should equivalent to:

template <class forwarditerator, class generator>   void generate ( forwarditerator first, forwarditerator last, generator gen ) {   while (first != last) {     *first = gen();     ++first;   } } 

but when try fill matrix 0-99 numbers. instead 10 rows of 0-9. why that?

std::vector< std::vector<int> > m;  #ifdef generate     struct generator{         int seq;         generator():seq(0){};         int operator()(){return seq++;};     } generator; #elif defined for_each     int = 0;     auto increment = [&i](int &a){a = i++;}; #endif  int x = 10, y = 10; m.resize(x); for(auto &v : m) {     v.resize(y);     #ifdef generate         generate(begin(v), end(v), generator);     #elif defined for_each         for_each(begin(v),end(v), increment);     #endif } 

you may use std::ref prevent copying of generator object:

generate(begin(v), end(v), std::ref(generator));