Hello,

Is it possible to cast a pointer to an integer to an array of integers?
My intention is to reserve a certain amount of integers with malloc. After
that I want to access those integers as if the reserved memory is an array of
integers, so I want to cast the integer pointer to an array of integers. Is
that possible or is there a way to address the reserved memory as an array?

Grtz, Arthur

#include <stdlib.h>

int main()
{
        int *iptr = malloc(4*sizeof(int));
        iptr[0] = 3;
        iptr[1] = 4;
        iptr[2] = 5;
        iptr[3] = 17;
        free(iptr);
        return 0;

The more usual method is to displace the int pointer to get to the other
integers, e.g.:

    int *p = malloc(10 * sizeof *p);

    /* ... check results of allocation ...  */

    p[3] = 5;

Less common is this:

    int (*p)[10] = malloc(sizeof *p);

    /* ... check results of allocation ...  */

    (*p)[3] = 5;

The syntax of using pointers to arrays is a little clumsy, since you always
have to parenthesize the *p, since the postfix [] has a greater precedence.
There is nothing like the -> operator for structures to simplify the use.

Pointers to arrays are useful for abstraction and encapsulation purposes.
That is, you can declare an array type as an abstract data type and pass
pointers to that type. Eric Young's encryption library LibDES does this
with its  des_cblock  type, which represents an eight byte cipherblock.

It is declared:

    typedef unsigned char des_cblock[8];

Many LibDES functions take arguments of type ``pointer to des_cblock''.

A pointer to an array can be safely cast to a pointer to the first
element of the array and vice versa. Thus if you were implementing the
LibDES functions, you could cast the pointer to des_block to a pointer
to unsigned char and then work with simpler syntax.

You certainly can:

  int   *pInt;
  ...
  pInt = malloc( MAXINTS*sizeof(int) );
  ...
  for( i=0; i<MAXINTS; i++ ) {
    sum += pInt[i];
    ...[or]...
    sum += *(pInt+i);
  }
  ...

Yours,

Geoff Houck
systems hk

http://www.teleport.com/~hksys
[Delete the "2" in eMail address to respond]

Some extra info: the array of integers are being used in a couple of
functions, so I just want to pass the pointer (to this array) to those
functions. Now I know the value of the "2nd dimension" ([][this_one]), which
is btw variable and is passed to the functions as well. Now I tried to define
the function with the pointer to the array and the value of the "2nd
dimension" something like this (it only doesn't work):

Call:

int *m, a;
/* malloc etc. */
matrix_func(m, a);

Function:

int matrix_func(int matrix[][n], int nr_i)

Where 'n' is a variable that indicates the size of the "2nd dimension" (and
is btw equal to 'nr_i').
However, using 'n' in the defintion doesn't seem to be allowed, it must be a
constant.

Greetings, Arthur

Groovy hepcat Arthur Rinkel was jivin' on Wed, 18 Jun 97 13:31:05 GMT
in comp.lang.c.
int pointer to int array again's a cool scene! Dig it!

int matrix_func(int *matrix, int width, int height);

#define ARRAY_WIDTH 80
#define ARRAY_HEIGHT 25
int *array;

array = malloc(ARRAY_WIDTH * ARRAY_HEIGHT * sizeof(int));

...    /* do something to the data array points to */

matrix_func(array, ARRAY_WIDTH, ARRAY_HEIGHT);

  This ensures matrix_func() knows the dimentions of the array so it
doesn't try to access data beyond the end of the array.

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============= Ain't I'm a dawg!! ==============

Groovy hepcat Arthur Rinkel was jivin' on Tue, 17 Jun 97 18:18:44 GMT
in comp.lang.c.
int pointer to int array's a cool scene! Dig it!

#define ARRAY_LEN 100  /* array length = 100 elements */
int *array;    /* declare a pointer to int */

array = malloc(ARRAY_LEN * sizeof(int));  /* allocate enough memory
for array of 100 int elements */

  Then to access an element of the array, you can simply use it the
same way you would any other array:

i = array[element];  /* assuming i and element have been declared, and
element is initialised to a valid subscript of array */

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-------------- Shaggy was here! ---------------
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============= Ain't I'm a dawg!! ==============