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

In C++0x you will be able to do it in the same way that you did with an array, but not in the current standard.

With only language support you can use:

int tmp[] = { 10, 20, 30 };
std::vector<int> v( tmp, tmp+3 ); // use some utility to avoid hardcoding the size here

If you can add other libraries you could try boost::assignment:

vector<int> v = list_of(10)(20)(30);

To avoid hardcoding the size of an array:

// option 1, typesafe, not a compile time constant
template <typename T, std::size_t N>
inline std::size_t size_of_array( T (&)[N] ) {
   return N;
}
// option 2, not typesafe, compile time constant
#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))

// option 3, typesafe, compile time constant
template <typename T, std::size_t N>
char (&sizeof_array( T(&)[N] ))[N];    // declared, undefined
#define ARRAY_SIZE(x) sizeof(sizeof_array(x))

Answer 2

The easiest way to do it is:

vector<int> ints = {10, 20, 30};

Answer 3

In C++11:

static const int a[] = {10, 20, 30};
vector<int> vec (begin(a), end(a));

Answer 4

you can do that using boost::assign.

vector<int> values;  
values += 1,2,3,4,5,6,7,8,9;

detail here

Answer 5

Related, you can use the following if you want to have a vector completely ready to go in a quick statement (e.g. immediately passing to another function):

#define VECTOR(first,...) \
   ([](){ \
   static const decltype(first) arr[] = { first,__VA_ARGS__ }; \
   std::vector<decltype(first)> ret(arr, arr + sizeof(arr) / sizeof(*arr)); \
   return ret;})()

example function

template<typename T>
void test(std::vector<T>& values)
{
    for(T value : values)
        std::cout<<value<<std::endl;
}

example use

test(VECTOR(1.2f,2,3,4,5,6));

though be careful about the decltype, make sure the first value is clearly what you want.

Answer 6

Before C++ 11 :

Method 1=>

vector<int> v(arr, arr + sizeof(arr)/sizeof(arr[0]));
vector<int>v;

Method 2 =>

 v.push_back(SomeValue);

C++ 11 onward below is also possible

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