C++ std::vector Initializing a std::vector
Example
A std::vector can be initialized in several ways while declaring it:
C++11
std::vector<int> v{ 1, 2, 3 }; // v becomes {1, 2, 3}
// Different from std::vector<int> v(3, 6)
std::vector<int> v{ 3, 6 }; // v becomes {3, 6}
// Different from std::vector<int> v{3, 6} in C++11
std::vector<int> v(3, 6); // v becomes {6, 6, 6}
std::vector<int> v(4); // v becomes {0, 0, 0, 0}
A vector can be initialized from another container in several ways:
Copy construction (from another vector only), which copies data from v2:
std::vector<int> v(v2);
std::vector<int> v = v2;
C++11
Move construction (from another vector only), which moves data from v2:
std::vector<int> v(std::move(v2));
std::vector<int> v = std::move(v2);
Iterator (range) copy-construction, which copies elements into v:
// from another vector
std::vector<int> v(v2.begin(), v2.begin() + 3); // v becomes {v2[0], v2[1], v2[2]}
// from an array
int z[] = { 1, 2, 3, 4 };
std::vector<int> v(z, z + 3); // v becomes {1, 2, 3}
// from a list
std::list<int> list1{ 1, 2, 3 };
std::vector<int> v(list1.begin(), list1.end()); // v becomes {1, 2, 3}
C++11
Iterator move-construction, using std::make_move_iterator, which moves elements into v:
// from another vector
std::vector<int> v(std::make_move_iterator(v2.begin()),
std::make_move_iterator(v2.end());
// from a list
std::list<int> list1{ 1, 2, 3 };
std::vector<int> v(std::make_move_iterator(list1.begin()),
std::make_move_iterator(list1.end()));
With the help of the assign() member function, a std::vector can be reinitialized after its construction:
v.assign(4, 100); // v becomes {100, 100, 100, 100}
v.assign(v2.begin(), v2.begin() + 3); // v becomes {v2[0], v2[1], v2[2]}
int z[] = { 1, 2, 3, 4 };
v.assign(z + 1, z + 4); // v becomes {2, 3, 4}
