Difference between two methods of creating of 2d array

What is the difference between two arrays definitions? Are they realized different in memo开发者_如何学Pythonry?

 int var = 5;
 int (*p4)[2] = new int [var][2]; // first 2d array

 int** p5 = new int*[var];  // second 2d array
 for(int i = 0; i < var; ++i){
     p5[i] = new int[2];
 }   

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Yes, they're very different. The first is really a single array; the second is actually var+1 arrays, potentially scattered all over your RAM. var arrays hold the data, and one holds pointers to the var data arrays.

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The first is an ordinary, fully contiguous array, the second is also known as jagged array or lliffe vector and can e.g. be used to represent triangular structures.