returning af struct

[kemsa]

Hello;

I´m struggling with a program, which I want to return a struct.

My program looks like this:

void make_bookingliste()
{
/* Disse konstanter definerer vore øvre og nedre grænse. Bruges til rand() */
const int LOW = 1;
const int HIGH = sizeof (personer) / sizeof (struct typer);

int k, j, tal;

struct typer liste[400];

/* Erklærer variabel til at indeholde sekunder på uret */
time_t sekunder;
/* Få værdien fra system-klokken og placer det i variablen sekunder */
time(&sekunder);
/* Konvertér sekunder til en unsigned integer */
srand((unsigned int) sekunder);

printf("Navn\t\t\t\t\tVIP (1 = VIP)\n");
printf("-----------------------------------------------------------------\n");

for(k = 1 ; k <= 140 ; k++)
{
tal = rand() % (HIGH - LOW) + LOW;

printf("%d ", k);

if(k <= 12)
personer[tal].vip = 1;
else
personer[tal].vip = 0;

liste[tal] = personer[tal];

print_typer (&personer[tal]);
}
}

Now, I would like this funktion to return the struct "list", which should be a copy of "personer". How is that possible? Thanks...

 

[marsd]

Liste is an array of structs declared statically
and locally. You cannot return an array.
What you can do is allocate the array and return
a pointer to it.

struct typer *liste = malloc(400 * sizeof(struct typer));
/* rest of your code */
return liste;

 

[kemsa]

Dou you mean something like that. (And thank you for your quick answer):

void make_bookingliste()
{
struct typer *liste = malloc(400 * sizeof(struct typer));
/* Disse konstanter definerer vore øvre og nedre grænse. Bruges til rand() */
const int LOW = 1;
const int HIGH = sizeof (personer) / sizeof (struct typer);
int k, j, tal;

/* Erklærer variabel til at indeholde sekunder på uret */
time_t sekunder;
/* Få værdien fra system-klokken og placer det i variablen sekunder */
time(&sekunder);
/* Konvertér sekunder til en unsigned integer */
srand((unsigned int) sekunder);

printf("Navn\t\t\t\t\tVIP (1 = VIP)\n");
printf("-----------------------------------------------------------------\n");

for(k = 1 ; k <= 140 ; k++)
{
tal = rand() % (HIGH - LOW) + LOW;

printf("%d ", k);

if(k <= 12)
personer[tal].vip = 1;
else
personer[tal].vip = 0;

liste[tal] = personer[tal];

print_typer (&personer[tal]);
}
return liste;

}

 

[marsd]

lude <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>

#define RANDOMSTRING(l,str) {int i = 0; while (i < l) {str[i] = (char)(1 + rand() % 127); ++i;} str[i] = '\0';}
#define BSZ 256
#define ALEN 10

typedef struct mytype
{
  int vip;
  char record[BSZ];
} M;



M *retM (int);
void printIt (M *, int);
void head (void);
void foot (void);

int
main (void)
{
  M *foo = NULL;

  foo = retM (ALEN);
  printIt (foo, ALEN);
  return 0;
}

M *
retM (int sz)
{
  int y = 0;
  char buf[BSZ];
  M *foo1 = malloc (sz * sizeof (M));

  if (foo1 == NULL)
    {
      return NULL;
    }
  while (y < sz)
    {
      RANDOMSTRING (BSZ, buf);
      strncpy (foo1[y].record, buf, BSZ);
      foo1[y].vip = (y % 4 == 0 ? 1 : 0);
      ++y;
    }
  return foo1;
}


void
printIt (M * thing, int len)
{
  int y = 0;

  while (y < len)
    {
      /*head(); */
      printf ("\n\nElement at %d , with vip value = %d and record = %s\n\n",
	      y, thing[y].vip, thing[y].record);
      /*foot(); */
      ++y;
    }
  return;
}

An example.