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 DEBIAN

px_put_recordn

PX_PUT_RECORDN(3)					     Library Functions Manual						 PX_PUT_RECORDN(3)

NAME

       PX_put_recordn -- Stores record in Paradox file at certain position

SYNOPSIS

       #include <paradox.h>

       int PX_put_recordn(pxdoc_t *pxdoc, char *data, int recpos)

DESCRIPTION

       Stores  a  record  in the buffer data into a Paradox file at the given position recpos.	The first position has number 0. The function will
       determine the data block for this record. If the position is after the last data block, then as many as needed empty data  blocks  will	be
       added.  If the position is in the middle of a data block and there is no record right before the position, then the position will be recal-
       culated to make sure the new record will be stored in the first free slot of the datablock. For example, if a datablock contains H  records
       and  the first call of PX_put_recordn wants to store a record at postion 11, then this will be corrected to position H. PX_put_recordn will
       also add an empty data block and store the record as the first record of the second data block.	Storing a second  record  at  position	11
       again, will be executed without any position change.

       data  must  be constructed with PX_put_data_xxx(3) functions before. It is of the same structure as the record returned by PX_get_record(3)
       and PX_get_record2(3).

RETURN VALUE

       Returns the record position on success and -1 on failure. The first position has number 0.

SEE ALSO

       PX_get_record(3), PX_get_record2(3), PX_put_record(3),  PX_put_data_byte(3),  PX_put_data_short(3),  PX_put_data_long(3),  PX_put_data_dou-
       ble(3), PX_put_data_alpha(3)

AUTHOR

       This manual page was written by Uwe Steinmann uwe@steinmann.cx.

																 PX_PUT_RECORDN(3)