How to define a 2D array in C++ and STL without memory manipulation?

Question

There are several ways to define a 2D array in C++ and STL without memory manipulation, and the following codes illustrate two different methods:

int main () 
{
         


        

Answer 1

To declare a 2D array using std::vector, you can use this kind of construction:

vector >  matrix( n, vector(m, -1) );

This creates a 2D array matrix of size n by m, with all elements initialised to -1.

It's basically a nesting of the "initialise with n items of value val" constructor:

vector (size_type n, const value_type& val,
                 const allocator_type& alloc = allocator_type());

(constructor definition copied from here)