realloc and Segmentation Fault

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realloc and Segmentation Fault
\ Jonathan Shan (19 Jul 2006)
. \ Vladimir Vassilev (19 Jul 2006)
. . \ Jonathan Shan (19 Jul 2006)
. . . \ Andrew Haley (19 Jul 2006)
. . . . \ Jonathan Shan (19 Jul 2006)
. . . . . \ Rupert Wood (20 Jul 2006)
. . . . . . \ Jonathan Shan (20 Jul 2006)
. . . . . . . \ Rupert Wood (21 Jul 2006)
. . . . . . . . \ Jonathan Shan (21 Jul 2006)

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Subject:	realloc and Segmentation Fault
Group:	Gcc-help
From:	Jonathan Shan
Date:	19 Jul 2006

Hello all,

The goal of my program is to create a dynamic array of a struct type. The
struct type has two strings inside it. From time to time I want to copy
strings into the strings in the dynamic array. Then increase the size of
the dynamic array. I have narrowed the problem down to the realloc
function but I still don't know why it says segmentation fault or hangs
(sometimes).

Here is the simplified code which exhibits the problem:

/*libraries here */

#define SIZEOF_BUCKETSTRUCT 70
#define SIZEOF_HOSTNAME 20
#define SIZEOF_DESCRIPTION 50

int bucketsize = 1;
struct bucket
{
char *hostname;
char *description;
};
void function1(struct bucket *valid)
{
valid[bucketsize - 1].hostname = malloc (sizeof(char) * 20);
strncpy(valid[bucketsize - 1].hostname, "test hostname", 20);
valid[bucketsize - 1].hostname[19] = '\0';
printf("hostname is %s \n", valid[bucketsize - 1].hostname);

valid[bucketsize - 1].description = malloc (sizeof(char) * 50);
strncpy(valid[bucketsize - 1].description, "test buf", 50);
valid[bucketsize - 1].description[49] = '\0';
printf("description is %s \n", valid[bucketsize - 1].description);
/* problem is here */
valid = (struct bucket *) realloc (valid, 70 * ((bucketsize) +
1));
bucketsize++;
}
int main()
{
struct bucket *valid;
valid = (struct bucket *) malloc (SIZEOF_BUCKETSTRUCT);
if (valid == NULL)
{
printf("error in allocating memory \n");
exit(1);
}

function1(valid);
function1(valid);

return 0;
}

Thank you,

Jonathan Shan