Re: std::vector construction

From:

ZikO <zebik@op.pl>

Newsgroups:

comp.lang.c++

Date:

Fri, 13 Feb 2009 15:04:12 +0000

Message-ID:

<gn425e$u5f$1@news.onet.pl>

mlt wrote:

Is there someway to create a std::vector from a sequence of numbers? On this
page:

http://www.cppreference.com/wiki/stl/vector/vector_constructors

there are 4 different constructors, but none of them supports something
like:

std::vector<int> v = {1,2,3};

Its only possible to do it like:

std::vector<int> v;

v.push_back(1,2,3);

AFAIK you can't do that by constructor. You could however use generate()
or generate_n() algorythm in <algorithm> head file and fill empty vector
with values generated by Generator. You however, need, generator :P

Something like this

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

using namespace std;

class Gen { // generator
private:
    int value;
    int step;
public:
    Gen(int bb = 0, int ss = 1) : value(bb), step(ss) {}
    int operator()() {
        int old = value;
        value += step;
        return old;
    }
};

int main() {
    vector<int> v1;
    generate_n(back_inserter(v1), 50, Gen(1,1));

    vector<int> v2(50);
    generate(v2.begin(), v2.end(), Gen(0,5));

    for(int i=0; i<v1.size(); i++) {
        cout << v1[i] << " ";
    }
    cout << endl;

    for(int i=0; i<v2.size(); i++) {
        cout << v2[i] << " ";
    }
    cout << endl;
}

Hopefuly it helped.