Question

In my program, I have a vector of vector of ints. Now I want to take one vector from the vector of vectors and have it manipulated in another vector container, but I get the error…

|error: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >' to non-scalar type 'std::vector<int, std::allocator<int> >' requested|

An example of what I am trying to do is as follows….

#include <vector>
using namespace std;

vector<vector<int> > k (13,5);

void some_funct() {
    vector<int> new_v (k[2].begin(), k[2].end());  //This line is what throws the error
    //here I do some stuff with new_v (e.g. sort it)
}

I’m not sure what I am doing wrong. I tried a couple of things like assigning the begin() and end() iterators to const iterator types… vector<int>::const_iterator it = k[2].begin(); but that didn’t work either.

This should work (because k[x] would be a vector) but I don’t know what is going wrong. Any help is appreciated!

EDIT:

After revision of my code, I noticed that there actually was an error. Instead of doing vector<int> new_v (k[2].begin(),k[2].end()); I did vector<int> new_v = (k[2].begin(),k[2].end());.

I would like to thank Rob for giving me the initiative to copy and paste my code into SO, where I noticed my mistake.

Thank you for your help!

Answer 1

It is hard to know, because you haven’t posted your actual code into the question. I suspect that you mis-copied the code from your project into Stack Overflow.

The offending line in your project looks something like this:

vector<int> new_v = (k[2].begin(), k[2].end()); 

Note the extra =.

You are initializing new_v with an expression of type vector::iterator, which won’t work. The statement you typed into SO, however, will work:

vector<int> new_v (k[2].begin(), k[2].end()); 

As will this:

vector<int> new_v = vector(k[2].begin(), k[2].end());

Or either of these:

vector<int> new_v(k[2]);
vector<int> new_v = k[2];

See https://ideone.com/uK8Xg and the corresponding error message.