how to use variables in C++ in the gnuplot-iostream

I am using gnuplot-iostream for c++,my problem is like below:

 gp << "set object 1 rect from 3,1 to 3.2,4 fc lt 1 \n";

In the numbers of above, can we use some variables in c++ to replace them? and how to do that? Adding one rectangle is easy, but when I want to add more, that will be very intractable. I try several ways ,but it does not work. Thanks ahead!

Never used gnuplot-iostream, but maybe some vanilla C++ will help you, iostream is just a pipe to console, so you cant interrupt the buffer but concatenate information, you could do something like this:

 gp << "set object " << 1 << " rect from "
 << 3,1 << " to " << 3.2 << "," << 4 << " fc lt 1 \n";

But i suppose you don't want to do that.

I'd create a struct and overload the << operator to return whatever you need.

struct Rect {
  float from[2];
  float to[2];
}
std::ostream& operator<<(std::ostream& os, const Rect& obj)
{
    std::string formated = "from "
      + std::to_string(obj.from[0]) + ","
      + std::to_string(obj.from[1]) + " to "
      + std::to_string(obj.to[0])   + ","
      + std::to_string(obj.to[1]);

    os << formated;
    return os;
}

So you can just define rectangles and pass them to the stream

Rect r1 = {{2,41},{63,1.4}};
std::cout << r1; // "from 2,41 to 63,1.4"