linked list doubt

[mallik]

Hi,

I hav one structure like this

struct linked_list {
struct linked_list *next;
char *data;
};

struct linked_list *tmp = NULL;
char *test_string = "some data";
tmp = malloc(sizeof(*tmp));


strncpy(tmp->data,test_string,strlen(test_string));

iam getting error segmentation fault. can any body help me .


Thanks in Advance

[Franklin52]

tmp = malloc(sizeof(*tmp));

must be:

tmp = malloc(sizeof(struct linked_list));

You must also allocate memory for the member data of the struct.

Regards

[yugandhargv]

Hi,
You have to allocate memory of size struct linked list not of size *tmp because of sizeof(*tmp) allocates memory for the pointer not for the structure. That's why you are getting segmentation fault.
Try the following
tmp = malloc(sizeof(struct linked_list));

[Franklin52]

Hi,
You have to allocate memory of size struct linked list not of size *tmp because of sizeof(*tmp) allocates memory for the pointer not for the structure. That's why you are getting segmentation fault.
Try the following
tmp = malloc(sizeof(struct linked_list));

Is this a vital tidbit of information that I neglected to mention earlier?

Regards

[Sangal-Arun]

Shouldn't it be a good approach to type cast before assigning the bytes to tmp (structure pointer variable).

Is this a vital tidbit of information that I neglected to mention earlier?


Regards

[Cabhan]

In C, casts from (void *) are made automatically. In C++, you would need to specifically make the cast.

I suppose if it helps you to manually cast, it wouldn't hurt. But it's pretty rare to see it: we all know that malloc is allocating the memory for that structure.

[the_unforgiven]

The main reason for the segfault is

strncpy(tmp->data,test_string,strlen(test_string));

without allocating memory for tmp->data.

The statement

tmp = malloc(sizeof(*tmp));

is perfectly legal and valid.