Thanks your explanation of realloc helped.
I made a simple test program which worked, then I made a program which
passed 'valid' pointer around some functions and it did not compile with
error: conflicting types.
This is the simplest code which exhibits the error:
struct bucket
{
char *hostname;
char *description;
};
int bucketsize = 1;
void func1(struct bucket *valid)
{
func2(valid);
}
void func2(struct bucket *valid)
{
/*this code causes errors*/
valid = insert_to_bucket(valid);
}
struct bucket *insert_to_bucket(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);
valid = (struct bucket *) realloc (valid, 70 * ((bucketsize) +
1));
bucketsize++;
return valid;
}
int main()
{
struct bucket *valid;
valid = (struct bucket *) malloc (70);
if (valid == NULL)
{
printf("error in allocating memory \n");
exit(1);
}
struct bucket *insert_to_bucket();
/*the line directly below works*/
// valid = insert_to_bucket(valid);
/*the line directly below causes errors*/
func1(valid);
return 0;
}
On Wed, 19 Jul 2006, Vladimir Vassilev wrote:
Hello Jonathan,
There is bug in your program. The 'valid' pointer in 'main' has the same
value before and after the call to function1. The realloc call in function1
deallocates this memory allocates new one and returns the new address.
However in main you continue to use the now invalid address and use it in the
next call.
Probably you assume realloc just extends the already allocated memory and the
ptr remains the same which is not the case.
Regards,
Vladimir
Jonathan Shan wrote:
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
--
=========================================================================================
Vladimir Vassilev |
Logicom Consult EOOD | E-mail:
Mladost 1A, bl. 501, apt. 68 | vladimir@xxxxxxxxxxxxxx
Sofia, Bulgaria | Web:
Tel:+359 886979158 | http://www.logicom-bg.com
