What is the easiest way to initialize a std::vector with hardcoded elements?

Question

I can create an array and initialize it like this:

int a[] = {10, 20, 30};

How do I create a std::vector and initialize it sim

Answer 1

Below methods can be used to initialize the vector in c++.

1. int arr[] = {1, 3, 5, 6}; vector<int> v(arr, arr + sizeof(arr)/sizeof(arr[0]));

2. vector<int>v; v.push_back(1); v.push_back(2); v.push_back(3); and so on

3. vector<int>v = {1, 3, 5, 7};

The third one is allowed only in C++11 onwards.

Answer 2

One method would be to use the array to initialize the vector

static const int arr[] = {16,2,77,29};
vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

Answer 3

In case you want to have it in your own class:

#include <initializer_list>
Vector<Type>::Vector(std::initializer_list<Type> init_list) : _size(init_list.size()),
_capacity(_size),
_data(new Type[_size])
{
    int idx = 0;
    for (auto it = init_list.begin(); it != init_list.end(); ++it)
        _data[idx++] = *it;
}

Answer 4

In C++11:

#include <vector>
using std::vector;
...
vector<int> vec1 { 10, 20, 30 };
// or
vector<int> vec2 = { 10, 20, 30 };

Using boost list_of:

#include <vector>
#include <boost/assign/list_of.hpp>
using std::vector;
...
vector<int> vec = boost::assign::list_of(10)(20)(30);

Using boost assign:

#include <vector>
#include <boost/assign/std/vector.hpp>
using std::vector;
...
vector<int> vec;
vec += 10, 20, 30;

Conventional STL:

#include <vector>
using std::vector;
...
static const int arr[] = {10,20,30};
vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

Conventional STL with generic macros:

#include <vector>
#define ARRAY_SIZE(ar) (sizeof(ar) / sizeof(ar[0])
#define ARRAY_END(ar) (ar + ARRAY_SIZE(ar))
using std::vector;
...
static const int arr[] = {10,20,30};
vector<int> vec (arr, ARRAY_END(arr));

Conventional STL with a vector initializer macro:

#include <vector>
#define INIT_FROM_ARRAY(ar) (ar, ar + sizeof(ar) / sizeof(ar[0])
using std::vector;
...
static const int arr[] = {10,20,30};
vector<int> vec INIT_FROM_ARRAY(arr);

Answer 5

typedef std::vector<int> arr;

arr a {10, 20, 30};       // This would be how you initialize while defining

To compile use:

clang++ -std=c++11 -stdlib=libc++  <filename.cpp>

Answer 6

If you don't want to use boost, but want to enjoy syntax like

std::vector<int> v;
v+=1,2,3,4,5;

just include this chunk of code

template <class T> class vector_inserter{
public:
    std::vector<T>& v;
    vector_inserter(std::vector<T>& v):v(v){}
    vector_inserter& operator,(const T& val){v.push_back(val);return *this;}
};
template <class T> vector_inserter<T> operator+=(std::vector<T>& v,const T& x){
    return vector_inserter<T>(v),x;
}