Thread: list head

In C++, this would normally give me my first node with head and curr pointing to it and next would be '\0'.

Data *head, *curr;
head=new Data;
curr=head ;
curr->next=NULL;

Now to implement this in C, would I need something like this :

struct Data *head, *curr;
head=(Data*)malloc(sizeof (Data)); //is this the same a new??
curr=head;
curr->next=NULL;

and then to create another node, would I need to do
curr->next=malloc(sizeof *Data);

One last thing...can I increase or decrease the size of an array within the struct (according to user input) e.g

char name[20] to char name [30]

cheers
sophie

>pointing to it and next would be '\0'
[pedantic]
'\0' is a character with all bits zero, called a NUL. When a pointer points to nowhere it is called NULL. The two are not interchangeable.
[/pedantic]

>head=(Data*)malloc(sizeof (Data)); //is this the same a new??
Yes, but in C you can write it better and it's always a good idea to check that malloc did not return NULL.
if ( ( head = malloc ( sizeof *head ) ) != NULL )

>can I increase or decrease the size of an array within the struct (according to user input)
Yes, but you have to use dynamic arrays by declaring them as char *, allocating the initial size and then resizing with realloc.

-Prelude

I've just gone through the manual about realloc and it makes no sense to...I have no idea as to how I should be implementing it.

Ohh is this what you meant by initializing it as char * e.g

struct Node
{
char *name[20];
int * id [5];
struct Node *next;
};

>Ohh is this what you meant by initializing it as char *
Not quite:

Code:

/* pseudocode */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct test
{
  char *name;
};

static void resize ( char * a )
{
  char *temp;
  if ( ( temp = realloc ( a, 13 * sizeof *a ) ) != NULL )
    a = temp;
}


int main ( void )
{
  struct test a;
  if ( ( a.name = malloc ( 6 * sizeof a.name ) ) != NULL ) {
    strcpy ( a.name, "Fooby" );
    puts ( a.name );
    resize ( a.name );
    strcpy ( a.name, "Fooby Rules!" );
    puts ( a.name );
    free ( a.name );
  }
  return 0;
}

-Prelude