Problem with linked lists Post: 302277010

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Top Forums Programming Problem with linked lists Post 302277010 by spirtle on Thursday 15th of January 2009 06:07:25 AM

01-15-2009

Registered User

This line is dodgy:

Code:

data[0].friends=malloc(2*sizeof(struct record));

record::friends is of type pointer to pointer to struct record, but you are allocating space for two structs, which isn't the same thing. You need friends to point to the memory you allocated.
Try this

Code:

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

struct record {
  int id;
  struct record **friends;
};

void subroutine(struct record **data){
    int i;
    *data=malloc(3*sizeof **data);
    struct record* friends = malloc(2*sizeof *friends);
    (*data)[0].friends=&friends;
    for(i=0;i<3;i++) (*data)[i].id=i;
    (*data)[0].friends[0]=data[1];
    printf("%d %d\n", (*data)[0].id, (*data)[0].friends[0]->id);
}

int main(){
    int i;
    struct record *data;

/* This uncommented piece of code works as it is supposed to */
  data=malloc(3*sizeof *data);
  struct record* friends = malloc(2*sizeof *friends);
  data[0].friends=&friends;
  for(i=0;i<3;i++) data[i].id=i;
  data[0].friends[0]=&data[1];
  printf("%d %d\n", data[0].id, data[0].friends[0]->id);

  struct record *data1;
  subroutine(&data1);
  return EXIT_SUCCESS;
}

spirtle

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LEARN ABOUT OSX

xml::libxml::nodelist

XML::LibXML::NodeList(3)				User Contributed Perl Documentation				  XML::LibXML::NodeList(3)

NAME

       XML::LibXML::NodeList - a list of XML document nodes

DESCRIPTION

       An XML::LibXML::NodeList object contains an ordered list of nodes, as detailed by the W3C DOM documentation of Node Lists.

SYNOPSIS

	 my $results = $dom->findnodes('//somepath');
	 foreach my $context ($results->get_nodelist) {
	   my $newresults = $context->findnodes('./other/element');
	   ...
	 }

API

   new(@nodes)
       You will almost never have to create a new NodeList object, as it is all done for you by XPath.

   get_nodelist()
       Returns a list of nodes, the contents of the node list, as a perl list.

   string_value()
       Returns the string-value of the first node in the list.	See the XPath specification for what "string-value" means.

   to_literal()
       Returns the concatenation of all the string-values of all the nodes in the list.

   get_node($pos)
       Returns the node at $pos. The node position in XPath is based at 1, not 0.

   size()
       Returns the number of nodes in the NodeList.

   pop()
       Equivalent to perl's pop function.

   push(@nodes)
       Equivalent to perl's push function.

   append($nodelist)
       Given a nodelist, appends the list of nodes in $nodelist to the end of the current list.

   shift()
       Equivalent to perl's shift function.

   unshift(@nodes)
       Equivalent to perl's unshift function.

   prepend($nodelist)
       Given a nodelist, prepends the list of nodes in $nodelist to the front of the current list.

   map($coderef)
       Equivalent to perl's map function.

   grep($coderef)
       Equivalent to perl's grep function.

   sort($coderef)
       Equivalent to perl's sort function.

       Caveat: Perl's magic $a and $b variables are not available in $coderef. Instead the two terms are passed to the coderef as arguments.

   reverse()
       Equivalent to perl's reverse function.

   foreach($coderef)
       Inspired by perl's foreach loop. Executes the coderef on each item in the list. Similar to "map", but instead of returning the list of
       values returned by $coderef, returns the original NodeList.

   reduce($coderef, $init)
       Equivalent to List::Util's reduce function. $init is optional and provides an initial value for the reduction.

       Caveat: Perl's magic $a and $b variables are not available in $coderef. Instead the two terms are passed to the coderef as arguments.

perl v5.16.2							    2012-10-22						  XML::LibXML::NodeList(3)