Cracking the Coding Interview - Fooo

Solutions to Chapter 16 | Low Level
16 10 Write a function called my2DAlloc which allocates a two dimensional array Minimize
the number of calls to malloc and make sure that the memory is accessible by the
notation arr[i][j]
SOLUTION
We will use one call to malloc
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pg 82
Allocate one block of memory to hold the row vector and the array data The row vector will
reside in rows * sizeof(int*) bytes The integers in the array will take up another rows * cols *
sizeof(int) bytes
Constructing the array in a single malloc has the added benefit of allowing disposal of the
array with a single free call rather than using a special function to free the subsidiary data
blocks
1 #include
2
3 int** My2DAlloc(int rows, int cols) {
4 int header = rows * sizeof(int*);
5 int data = rows * cols * sizeof(int);
6 int** rowptr = (int**)malloc(header + data);
7 int* buf = (int*)(rowptr + rows);
8 int k;
9 for (k = 0; k < rows; ++k) {
10 rowptr[k] = buf + k*cols;
11 }
12 return rowptr;
13 }
2 4 8