A 2D array reallocation in C - c

Question

I know this has been discussed here plenty of times, but I simply cannot see what I'm doing wrong. Here's the snippet.
#include <stdio.h>
#include <stdlib.h>
double** SEG = NULL;
void main ()
{
int i;
int seg_counter = 0;
SEG = (double**) malloc(1 * sizeof(double *));
for(i=0; i < 1; i++)
{
*(SEG + i) = (double*) malloc(9 * sizeof(double));
}
while (1)
{
SEG = (double**) realloc(SEG, seg_counter+1 * sizeof(double *));
for(i=seg_counter; i < seg_counter+1; ++i)
{
*(SEG + i) = (double*) malloc(9 * sizeof(double));
}
printf ("%d\n", seg_counter);
seg_counter++;
}
}
The goal is to add one row each time the loop is executed. I'm getting a memory error instead.
Thnx for any help here!

Answer 1

You do not have a 2D array only an array of pointers. You can have real 2D if you use array pointers.
Do not use types only objects in the sizeof
void *addRow(size_t *rows, const size_t cols, double (*array)[cols])
{
array = realloc(array, (*rows + 1) * sizeof(*array));
if(array) *rows += 1;
return array;
}
int main(void)
{
size_t cols = 10, rows = 0;
double (*array)[cols] = NULL;
for(size_t i = 0; i < 10; i ++)
{
void *tmp;
tmp = addRow(&rows, cols, array);
if(tmp)
{
array = tmp;
printf("Added another row!!!!! Rows = %zu\n", rows);
}
}
free(array);
}
You can also add some checks.
void *addRow(size_t *rows, const size_t cols, double (*array)[*rows])
{
if(rows && cols)
{
array = realloc(array, (*rows + 1) * sizeof(*array));
if(array) *rows += 1;
}
return array;
}

Answer 2

For starters you should set the variable seg_counter to 1 after this memory allocation
int seg_counter = 0;
SEG = (double**) malloc(1 * sizeof(double *));
++seg_counter;
Or you could write
int seg_counter = 1;
SEG = (double**) malloc( seg_counter * sizeof(double *));
Then the following for loop (that is in fact redundant) will look like
for(i=0; i < seg_counter; i++)
{
*(SEG + i) = (double*) malloc(9 * sizeof(double));
}
This statement
SEG = (double**) realloc(SEG, seg_counter+1 * sizeof(double *));
has a typo, You need to write
SEG = (double**) realloc(SEG, ( seg_counter+1 ) * sizeof(double *));
Again the next for loop is redundant. You could just write
*(SEG + seg_counter) = (double*) malloc(9 * sizeof(double));
and then
seg_counter++;
printf ("%d\n", seg_counter);
As you have an infinite while loop then your program will be aborted when memory can not be allocated.