fp*****@yahoo.co.uk (Isaac) wrote in message news:<88**************************@posting.google. com>...
Hi mates
I want to know a simple program of return array from function ? Do I
need to use pointer to return the address of the first element in an
array.
Isaac
This covers most of the possible variations. The first two methods
are the most common (using pointers to the base type, rather than
pointers to arrays of the base type).
#include <stdlib.h>
#include <stdio.h>
/*
** Allocate space to hold _size_ ints, return pointer to
** base address as function return value. This is the
** most common method.
*/
int *newa1 (size_t size)
{
int *ap;
ap = malloc (sizeof *ap * size);
if (!ap)
{
printf ("newa1: malloc failed\n");
}
return ap;
}
/*
** Allocate space to hold _size_ ints, return pointer to
** base address as function parameter
*/
void newa2 (size_t size, int **ap)
{
*ap = malloc (sizeof **ap * size);
if (!*ap)
{
printf ("newa2: malloc failed\n");
}
}
/*
** Allocate space for fixed-size array of int, return pointer
** to array as function return value. Not generally used,
** since array sizes are fixed and must be known ahead of time.
**
** The declaration reads as
**
** newa3 -- newa3
** is a function -- newa3()
** taking no parameters -- newa3(void)
** returning a pointer -- *newa3(void)
** to a 10 element array -- (*newa3(void))[10]
** of int -- int (*newa3(void))[10]
*/
int (*newa3 (void))[10]
{
int (*ap)[10];
ap = malloc (sizeof *ap);
if (!*ap)
{
printf ("newa3: malloc failed\n");
}
return ap;
}
/*
** Allocate space for a fixed-size array of int, return pointer
** to array as function parameter
*/
void newa4 (int (**ap)[20])
{
*ap = malloc (sizeof **ap);
if (!*ap)
{
printf ("newa4: malloc failed\n");
}
}
int main (void)
{
int *a1, *a2; /* a1 and a2 are pointers to int */
int (*a3)[10], (*a4)[20]; /* a3 and a4 are pointers to arrays of
int */
int i;
a1 = newa1 (10); /* function call */
if (a1) /* test */
a1[0] = 0; /* assignment */
newa2 (20, &a2);
if (a2)
a2[1] = 1;
a3 = newa3 ();
if (a3)
(*a3)[2] = 2;
newa4 (&a4);
if (a4)
(*a4)[3] = 3;
return 0;
}
Important things to remember:
a1, a2 -- pointers to int.
*a1, *a2 -- int values
a3, a4 -- pointers to arrays of int
*a3, *a4 -- arrays of int values
The spaces that a1 and a2 point to may be resized using realloc().
The spaces pointed to by a3 and a4 may not be resized.
*a1 = 0; /* legal, equivalent to a1[0] = 0; */
*a3 = 0; /* illegal; *a3 is an array type, not an int type */
IME, using pointers to arrays (a3 and a4) is not very common, since
the primary reasons you're using dynamic memory are a) you don't know
how much space you'll need until runtime, and b) you want to be able
to resize that space as needed. However, I thought I'd toss that in
for completeness' sake.
