函子编译时错误

Question

My code -

#include <iostream>
#include <vector>
#include <string>
#include <sstream>
using namespace std;

#include "boost\numeric\ublas\matrix.hpp"

typedef boost::numeric::ublas::matrix<float> matrix;


class FillMat{  
public:
    FillMat(float valIn) : val(valIn){}
    float operator()(float in) {
        val = in + 1;
        return val;
    }
private:
    float val;
};

typedef boost::numeric::ublas::matrix<float> matrix;
int main(){
    matrix m1(10, 20);
    float init = 22.2;
    FillMat myFiller(init);

    generate(m1.begin2(), m1.begin2() + m1.size1()*m1.size2(), myFiller);


    return 0;
}

When I try to compile the code, I get the following compile time error.

Error   3   error C2064: term does not evaluate to a function taking 0 arguments    

Can someone please tell me why?

PS I added the headers. I am using Boost matrix for 2D array.

Answer 1

The signature of the functor you pass to std::generate must take zero arguments.

This is stated in documentation .

Unfortunately, you didn't tell us what you are trying to do, so I can't suggest a fix for you.

Answer 2

A possible fix would be to change:

  float operator()(float in) {
        val = in + 1;
        return val;
    }

into:

   float operator()( void ) {
        float rv = val;
        val = val + 1.0;
        return rv;
    }

If that does what you want , that is the question ...

Answer 3

The function you're looking for is std::transform :

std::transform(m1.begin2(),
               m1.begin2() + m1.size1() * m1.size2(),
               m1.begin2(),
               myFiller);

Answer 4

Based on the clarification in the comment ("I am trying to fill the contents of my container such with incrementing values") what you really want is std::iota . I haven't quite gotten straight what you're trying to do with your matrix , and how you want the values to increment (row-wise or column-wise), so I'll give a demo with a normal vector, and let you figure out how to apply it in your actual situation:

std::vector<int> v(10);

std::iota(v.begin(), v.end(), 22.2);

for (auto i : v)
    std::cout << i << " ";

Should produce: 22.2 23.2 24.2 25.2 26.2 27.2 28.2 29.2 30.2 31.2