dynamic memory for 2D char array

Question

I have declared an array char **arr; How to initialize the memory for the 2D char array.

Answer 1

There are two options for allocating an array of type char **

I've transcribed these 2 code samples from the comp.lang.c FAQ (which also contains a nice illustration of these two array types)

Option 1 - Do one allocation per row plus one for the row pointers.

char **array1 = malloc(nrows * sizeof(char *)); // Allocate row pointers
for(i = 0; i < nrows; i++)
  array1[i] = malloc(ncolumns * sizeof(char));  // Allocate each row separately

Option 2 - Allocate all the elements together and allocate the row pointers:

char **array2 = malloc(nrows * sizeof(char *));      // Allocate the row pointers
array2[0] = malloc(nrows * ncolumns * sizeof(char)); // Allocate all the elements
for(i = 1; i < nrows; i++)
  array2[i] = array2[0] + i * ncolumns;

You can also allocate only one memory block and use some arithmetic to get at element [i,j]. But then you'd use a char* not a char** and the code gets complicated. e.g. arr[3*ncolumns + 2] instead of arr[3][2]