I want to initialize a vector like we do in case of an array.
Example
int vv[2] = {12, 43};
But when I do it like this,
vector<int> v(2) = {34, 23};
OR
vector<int> v(2);
v = {0, 9};
it gives an error:
expected primary-expression before ‘{’ token
AND
error: expected ‘,’ or ‘;’ before ‘=’ token
respectively.
This question is related to
c++
arrays
vector
declaration
With the new C++ standard (may need special flags to be enabled on your compiler) you can simply do:
std::vector<int> v { 34,23 };
// or
// std::vector<int> v = { 34,23 };
Or even:
std::vector<int> v(2);
v = { 34,23 };
On compilers that don't support this feature (initializer lists) yet you can emulate this with an array:
int vv[2] = { 12,43 };
std::vector<int> v(&vv[0], &vv[0]+2);
Or, for the case of assignment to an existing vector:
int vv[2] = { 12,43 };
v.assign(&vv[0], &vv[0]+2);
Like James Kanze suggested, it's more robust to have functions that give you the beginning and end of an array:
template <typename T, size_t N>
T* begin(T(&arr)[N]) { return &arr[0]; }
template <typename T, size_t N>
T* end(T(&arr)[N]) { return &arr[0]+N; }
And then you can do this without having to repeat the size all over:
int vv[] = { 12,43 };
std::vector<int> v(begin(vv), end(vv));
You can also do like this:
template <typename T>
class make_vector {
public:
typedef make_vector<T> my_type;
my_type& operator<< (const T& val) {
data_.push_back(val);
return *this;
}
operator std::vector<T>() const {
return data_;
}
private:
std::vector<T> data_;
};
And use it like this:
std::vector<int> v = make_vector<int>() << 1 << 2 << 3;
Source: Stackoverflow.com