Dynamically allocated 2D array of chars - unkwnown number of rows and columns

Dear All,

I am trying to solve a problem of dynamically allocated 2D array. My goal is to develop program that will scan at the input unknown number of sentences of unknown length in this format: "float number, colon, text" f.e:

30:How are you?
80:A dog is an animal.
35.5:I like ice cream and coke.
...

After the end of inputs, set of questions follows, user wants to find out whether there is matching pattern like:


Question:
> how
Found:
30:How are you?
Question:
> I like
Found:
35.5: I like ice cream and coke.
Question:
> Cat
Found:
nothing

At first I will have to probably save these sentences dynamically into 2D array with realloc function, but I do not know how to do that if I do not know the length of every sentence nor the number of sentences.

Thank you for your suggestions.

Quote:

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Originally Posted by arp35

At first I will have to probably save these sentences dynamically into 2D array with realloc function, but I do not know how to do that if I do not know the length of every sentence nor the number of sentences.

---

I suggest defining two structures like this:

Code:

---

struct sentence
{
    double number;
    char *text;
};

struct sentence_list
{
    struct sentence *sentences;
    size_t size;    // number of elements in use
    size_t capacity; // number of elements allocated
};

---

The idea is to read line by line, either using the non-standard (but POSIX standard) getline, or by defining your own version of getline with fgets in a loop to read the entire line of unknown length. You then parse this line (keeping in mind the colon) to get number and text, with which you then create a struct sentence object and insert it into the struct sentence_list object. If the size is about to exceed the capacity, you realloc the sentences for a new capacity (say 1.5 or 2 times the previous capacity).

If you are curious on how to allocate a bidimensional array, here's a tip:

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
  int i, j;
  int ( *ptr )[][20];  // ptr = pointer to bidimensional array of ints.
  size_t size;

  // Calc 10 rows needed space on heap.
  size = 10 * sizeof( int [20] );

  // Using calloc() to zero the entire array...
  ptr = calloc( 1, size );

  //...
  ( *ptr )[5][5] = 10;
  //...

  printf( "Allocated: %zu bytes @ %p\n", size, ptr );

  // show the array...
  for ( i = 0; i < 10; i++ )
  {
    printf( "row %-2d: ", i );

    for ( j = 0; j < 20; j++ )
      printf( "%3d ", ( *ptr )[i][j] );

    putchar( '\n' );
  }

  free( ptr );
}

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Thank you very much. 🙂