realloc array of structures

realloc array of structures

[J.]

Sunday, April 25 18:08:29

Hello, 

I am trying to put incomming data into an array of structures. For example
everytime a new line arrives, grow the array by one, and copy the line
into the newly allocated mem structure. 

Unfortunatly I am a bit lost in the pointer world. Could someone give me
some hints what to what goes wrong in the small example code below ?

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

struct node {
 char *str;
};

int main(void) {
 struct node **strarray = NULL;
 int i = 0, count = 0;
 char line[1024];
 
 while(fgets(line, 1024, stdin) != NULL) {
  /* grow the array with one element */
  strarray = (struct node **)realloc(strarray, (count + 1) * sizeof(struct node *));
  /* copy the line to member str of the new element (structure) */
  strarray[count++].str = strdup(line);
 }

 for(i = 0; i < count; i++)
  printf("[%d].str: %s", i, strarray[i].str);

 return 0;
}

/* any comments or suggestions are more then welcome.. Thnkx ! */
/* J. */

Re: realloc array of structures

[Jad Saklawi]

Quoting "J." <mailing-lists@xs4all.nl>:

> Sunday, April 25 18:08:29
> 
> Hello, 
> 
> I am trying to put incomming data into an array of structures. For example
> everytime a new line arrives, grow the array by one, and copy the line
> into the newly allocated mem structure. 
> 
> Unfortunatly I am a bit lost in the pointer world. Could someone give me
> some hints what to what goes wrong in the small example code below ?

Here is a fixed version of your code :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct node {
  char *str;
};

int main(void) {
  struct node **strarray = NULL;
  int i = 0, count = 0;
  char line[1024];

  while(fgets(line, 1024, stdin) != NULL) {
    /* grow the array with one element */
    strarray = (struct node **)realloc(strarray, (count + 1) * sizeof(struct
node *));
    strarray[count] = (struct node *)malloc(sizeof(struct node));
    /* copy the line to member str of the new element (structure) */
    strarray[count]->str =  strdup(line);
    count++;
  }

  for(i = 0; i < count; i++)
    printf("[%d].str: %s", i, strarray[i]->str);

  return 0;
}

  You needed to allocate memory for each struct, and you should use -> when
using struct pointers instead of .

Greets,
Jad Saklawi