iota increment vector of a class c++

问题

I recently have been taking advantage of the <numeric> iota statement for incrementing a vector of type int. But now I am trying to use the statement for incrementing an explicit class with 2 members.

So here is the usage with a vector of integers:

vector<int> n(6);
iota(n.begin(), n.end(), 1);

Given that Obj class has an integer member called m. The constructor initializes m to its corresponding integer argument. Here is what I am trying to do now:

vector<Obj> o(6);
iota(o.begin(), o.end(), {m(1)});

I've attempted making a class increment overload somewhat like this:

Obj& operator ++() {
    *this.m++;
    return *this;
}

But I think either my constructor is not designed for this overload or vice versa. How can I modify my constructor and overload to increment an object member with iota? Thanks in advance!

回答1:

I am not sure I understand your question. Does the following code match what you want?

#include <algorithm>
#include <iostream>
#include <vector>

class Object {
 public:
  Object(int value = 0)
      : m_value(value) { }
  Object& operator++() {
    m_value++;
    return *this;
  }
  int value() const {
    return m_value;
  }
 private:
  int m_value;
};

int main() {
  std::vector<Object> os(10);
  std::iota(os.begin(), os.end(), 0);
  for(const auto & o : os) {
    std::cout << o.value() << std::endl;
  }
}

Compiled with gcc 4.8 on OS X 10.7.4 I get:

$ g++ iota-custom.cpp -std=c++11
$ ./a.out 
0
1
2
3
4
5
6
7
8
9

回答2:

Updated: I changed the answer to provide the functionality requested in the comments: namely, to be able to update multiple fields.

Format your class in a manner similar to the following. You will need to overload the ++ operator to increment both _m and _c.

class Obj {
    private:
        int _m;
        char _c;

    public:
        Obj(int m, char c) : _m(m), _c(c)
        {
        }

        MyClass operator++()
        {
            _m++;
            _n++;

            return *this;
        }
};

The following code will initialize the vector o with 6 Obj's, each containing ascending values for _m and _c starting from 1.

vector<Obj> o(6);
iota(o.begin(), o.end(), Obj(1, 1));

回答3:

#include <numeric>      // std::iota
#include <vector>
using namespace std;

class Obj
{
private:
    int m_;
public:
    auto value() const -> int { return m_; }
    Obj( int m = 0 ): m_( m ) {}
};

auto main() -> int
{
    vector<Obj> v(6);
    iota( v.begin(), v.end(), 1 );
}

来源：https://stackoverflow.com/questions/26579703/iota-increment-vector-of-a-class-c

标签

c++

c++11

vector

overloading

increment