Problem
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.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.
int** My2DAlloc(int rows, int cols) { int header = rows * sizeof(int*); int data = rows * cols * sizeof(int); int** rowptr = (int**)malloc(header + data); int* buf = (int*)(rowptr + rows); int k; for (k = 0; k < rows; ++k) { rowptr[k] = buf + k*cols; } return rowptr; }
Here is a demo:
References
http://tianrunhe.wordpress.com/2012/04/23/allocate-a-two-dimensional-array-using-one-call-of-malloc-in-c/
0 comments:
Post a Comment