[OT] C programming problem

[OT] C programming problem

[Wol's lists]

It is for raid, honest :-)

My C is so rusty it's jammed solid :-) but I'm trying to prototype a 
simple algorithm for "de-clustering" a raid-60/61 array.

Googling for my error -

main.c:20:5: warning: incompatible implicit declaration of built-in 
function ‘memset’ [enabled by default]
      memset( &array, 0, blocks * sizeof(int) );

says "you need to include stdlib.h" - but I have!

(I'm getting the same error on the malloc ...)

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

void main()
{
     int disks, logdisks, mirrors, prime;

     printf( "%s", "Enter the number of disks ");
     scanf( "%d", &disks);
     printf( "%s", "Enter the number of logical disks ");
     scanf( "%d", &logdisks);
     printf( "%s", "Enter the number of mirrors ");
     scanf( "%d", &mirrors);
     printf( "%s", "Enter the prime ");
     scanf( "%d", &prime);

     int blocks, *array;

     blocks = logdisks * mirrors * disks;
     array = (int *) malloc( sizeof(int) * blocks );
     memset( &array, 0, blocks * sizeof(int) );

     int i;

     for (i=0; i < blocks; i++) {
         array[i] = (i * prime) % blocks;
     }

     for (i=0; i < blocks; i++) {
         if ( (i % disks) == 0)
             printf( "\n");
         printf( "%4d", array[i]);
     }
}

Re: [OT] C programming problem

[Linus Lüssing]

On Wed, Feb 07, 2018 at 07:46:13PM +0000, Wol's lists wrote:
> It is for raid, honest :-)
> 
> My C is so rusty it's jammed solid :-) but I'm trying to prototype a simple
> algorithm for "de-clustering" a raid-60/61 array.
> 
> Googling for my error -
> 
> main.c:20:5: warning: incompatible implicit declaration of built-in function
> ‘memset’ [enabled by default]
>      memset( &array, 0, blocks * sizeof(int) );
> 
> says "you need to include stdlib.h" - but I have!

You need to include string.h. See "man memset" (if your distro
has those).

I tried your code and I didn't get a warning or error for
malloc(). stdlib.h should be fine for malloc().

Re: [OT] C programming problem

[Michael Fritscher]

Hello,

> main.c:20:5: warning: incompatible implicit declaration of built-in
> function ‘memset’ [enabled by default]
>     memset( &array, 0, blocks * sizeof(int) );

at least my compiler says something about
> a.c:21:5: note: include ‘<string.h>’ or provide a declaration of ‘memset’

And yes, the first recipe does indeed help :-P

Best regards,
Michael Fritscher

Re: [OT] C programming problem

[Wol's lists]

On 07/02/18 20:00, Michael Fritscher wrote:
> Hello,
> 
>> main.c:20:5: warning: incompatible implicit declaration of built-in
>> function ‘memset’ [enabled by default]
>>      memset( &array, 0, blocks * sizeof(int) );
> 
> at least my compiler says something about
>> a.c:21:5: note: include ‘<string.h>’ or provide a declaration of ‘memset’
> 
> And yes, the first recipe does indeed help :-P
> 
Thank you both! Perfect!

I think actually stdlib had fixed the malloc problem, but I missed it 
because the memset problem was still there.

Cheers,
Wol

Re: [OT] C programming problem

[Phil Turmel]

Hi Wol,

Bug alert!

On 02/07/2018 02:46 PM, Wol's lists wrote:
> void main()
> {

>     blocks = logdisks * mirrors * disks;
>     array = (int *) malloc( sizeof(int) * blocks );
>     memset( &array, 0, blocks * sizeof(int) );
              ^^^^^^

Your 'array' variable is already a pointer.  You should not have
another address-of operator in front of it.  You are overwriting
your pointer and a bunch of static memory right after it, not
zeroing the area pointed to by 'array'.

Phil

Re: [OT] C programming problem

[Wol's lists]

On 07/02/18 22:43, Phil Turmel wrote:
> Hi Wol,
> 
> Bug alert!
> 
> On 02/07/2018 02:46 PM, Wol's lists wrote:
>> void main()
>> {
> 
>>      blocks = logdisks * mirrors * disks;
>>      array = (int *) malloc( sizeof(int) * blocks );
>>      memset( &array, 0, blocks * sizeof(int) );
>                ^^^^^^
> 
> Your 'array' variable is already a pointer.  You should not have
> another address-of operator in front of it.  You are overwriting
> your pointer and a bunch of static memory right after it, not
> zeroing the area pointed to by 'array'.
> 
Thanks. Somebody else already pointed out the error, but he was rather 
more "teacher", didn't tell me what exactly it was, and let me find it 
for myself!

Stupid mistake, but as I said, my C-fu is rusted solid :-)

Anyways, I've now got it sorted - I'll probably be posting it to the 
list as an RFC very soon ...

Cheers,
Wol