how is it working?

[sanketbarot]

Hello friends

suppose i want to defined a 2 dimensional array using pointer. for that i follow the following procedure(given in book). it is working perfactly but i am not getting it.

suppose row =2 and coloum =3
int **p;


p = new int*[2]; //Line 1

*p = new int[3]; /// line2
++*p = new int[3]; //line 3
++*p = new int[3; // Line 4



Now what exactly it is doing?

[Banfa]

p = new int*[2]; // 1 Allocates an array of integer pointers

*p = new int[3]; /// Allocates an array of integers and assigns it to the first entry in p

++*p = new int[3]; // Increment p to point to the second array entry allocated in 1, allocate an array of integers and assign it to this new location

++*p = new int[3]; // Increment p to point to the third array entry allocated in 1, however 1 only allocated 2 array entries so we are now pointing at unallocated data. Allocate an array of integers and assign it to this new location. Additionally since we haven't saved p we no longer and a reference to the originally allocated data so a memory leak may happen

It is equivilent to this

p = new int*[2];
p[0] = new int[3];
p[1] = new int[3];
p[2] = new int[3];

Just using pointer arithmatic rather than array notation.