CODEWITHSUNDEEP
c++generatoridioms
okman
okman

Reputation:

How can I implement a generator in C++?

I want to know how to implement a generator , like Python, in C++? Python can use keyword "yield" to do so. But how to do it in C++?

Upvotes: 17

Views: 10328

Answers (4)

artificialidiot
artificialidiot

Reputation: 5369

Calling a coroutine multiple times and getting different answers means you keep some state. The way to keep a state is objects. The way to make them look like function call is operator overloading. For some examples see the function object article in Wikipedia.

Upvotes: 3

xtofl
xtofl

Reputation: 41509

To elaborate on the iterator implementation: this is an example. It can be used as a loop variable, or in std algorithms.

#include <iterator>

template< typename T, typename TDiff = T >
struct TGenerator : public std::iterator<std::forward_iterator_tag,T,TDiff> {
  T from,to;
  T value;
  TDiff step;
  bool issentinel;

  TGenerator( T from, T to, TDiff step, bool sentinel = false )
    : from(from),to(to),step(step),issentinel(sentinel), value(from)
  {}

  void operator++(){ value += step; }

  const T& operator*()const { return value; }

  bool operator!=( const TGenerator& other ) const {
    return value<to;
  }

  TGenerator sentinel()const { return TGenerator(0,0,0,true); }

};


#include <algorithm>
#include <iostream>

int main()
{
  TGenerator<int> i(0,10,3);
  std::copy( i, i.sentinel(), std::ostream_iterator<int>( std::cout, " " ) );

    return 0;
}

Upvotes: 7

lurscher
lurscher

Reputation: 26953

you can use boost.context (sorry, not on boost distribution yet, you'll have to get it from boost vault).

A typical example code would be like this:

#include <iostream>
#include <boost/context.hpp>

using namespace std;

struct Parameters {
  int par1;
  float par2;
};

boost::context c1;
boost::context c2;

void F(void* parameters) {
  Parameters& pars = *(Parameters*)parameters;
  cout << pars.par1 << endl;
  c2.jump_to(c1);
  cout << pars.par2 << endl;
};

int main() {
  c1 = boost::context::current();
  Parameters p;
  p.par1 = 8;
  c2 = boost::context::create_context( F , c1 , p );
  c1.jump_to(c2);
  p.par2 = 1.3;
  c1.jump_to(c2);
}

Upvotes: 1

dave4420
dave4420

Reputation: 47052

You can't do it, really, but you can fake it. Here's a way you can fake it in C, which you can use in C++ as well.

Upvotes: 6

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