Allocate a 2d array in C with one dimension fixed

Question

I want to dynamically allocate 1 dimension of a 2D array (the other dimension is given). Does this work:

int NCOLS = 20;

// nrows = user input...

double *a         


        

Answer 1

You have to allocate a new array for each element (each element is a pointer to an array) on the first dimension. You can use a loop for that:

for(i = 0; i < NCOLS; i++)
   arr[i] = (double *)malloc(sizeof(double)*nrows);

Do the same to free.