Hi all!
I have this code:

------------------------------------------------------------------------------
ubyte N, M, K;
ubyte[][max][max] Matrix;

scanf("%d %d %d", &N, &M, &K);

ubyte tmp;

for(ubyte n = 1; n <= N; n++)
	for(ubyte m = 1; m <= M; m++)
	{
		scanf("%d", &tmp);
                // After this scanf n becomes 0 for no reason
		
                if(tmp) Matrix[m][tmp] ~= n;
        }

------------------------------------------------------------------------------

After scanf in loop variable n becomes 0. Is this a bug? Please help me!

Capture_A_Lag:

> After scanf in loop variable n becomes 0. Is this a bug? Please help me!

Have you tried to use a tmp of type int to avoid stomping?

Bye,
bearophile

On Wednesday, 16 April 2014 at 17:47:05 UTC, Capture_A_Lag wrote:
> Hi all!
> I have this code:
>
> ------------------------------------------------------------------------------
> ubyte N, M, K;
> ubyte[][max][max] Matrix;
>
> scanf("%d %d %d", &N, &M, &K);
>
> ubyte tmp;
>
> for(ubyte n = 1; n <= N; n++)
> 	for(ubyte m = 1; m <= M; m++)
> 	{
> 		scanf("%d", &tmp);
>                 // After this scanf n becomes 0 for no reason
> 		
>                 if(tmp) Matrix[m][tmp] ~= n;
>         }
>
> ------------------------------------------------------------------------------
>
> After scanf in loop variable n becomes 0. Is this a bug? Please help me!

I suppose it's because scanf wait for int variable (which 4 bytes), but you pass pointer to ubyte, and when you input data it overwrites neighbor bytes.

On Wed, 16 Apr 2014 17:47:03 +0000, Capture_A_Lag wrote:

> Hi all!
> I have this code:
> 
> 
------------------------------------------------------------------------------
> ubyte N, M, K;
> ubyte[][max][max] Matrix;
> 
> scanf("%d %d %d", &N, &M, &K);
> 
> ubyte tmp;
> 
> for(ubyte n = 1; n <= N; n++)
> 	for(ubyte m = 1; m <= M; m++)
> 	{
> 		scanf("%d", &tmp);
>                  // After this scanf n becomes 0 for no reason
> 
>                  if(tmp) Matrix[m][tmp] ~= n;
>          }
> 
> 
------------------------------------------------------------------------------
> 
> After scanf in loop variable n becomes 0. Is this a bug? Please help me!

You are using the wrong format spec for an unsigned ubyte; switch out all instances of "%d" with "%hhu" and it should work.  Short version: the "% d" instructs the C scanf function to overwrite 32bits of the stack starting at tmp which is only 8 bits long.

Even better than using the proper format spec, you could swap out the non- typesafe C functions and use the D equivalents readf and formattedRead (see std.stdio and std.format).

Justin

On 04/16/2014 10:47 AM, Capture_A_Lag wrote:

> ubyte tmp;

>          scanf("%d", &tmp);
>                  // After this scanf n becomes 0 for no reason

%d is for int.

Ali

P.S. A friendly request: It makes it much easier for the rest of the group if posts contained compilable, minimal but complete code. Thanks.

On Wednesday, 16 April 2014 at 17:47:05 UTC, Capture_A_Lag wrote:
> Hi all!
> I have this code:
>
> ------------------------------------------------------------------------------
> ubyte N, M, K;
> ubyte[][max][max] Matrix;
>
> scanf("%d %d %d", &N, &M, &K);
>
> ubyte tmp;
>
> for(ubyte n = 1; n <= N; n++)
> 	for(ubyte m = 1; m <= M; m++)
> 	{
> 		scanf("%d", &tmp);
>                 // After this scanf n becomes 0 for no reason
> 		
>                 if(tmp) Matrix[m][tmp] ~= n;
>         }
>
> ------------------------------------------------------------------------------
>
> After scanf in loop variable n becomes 0. Is this a bug? Please help me!

scanf is inherently unsafe routine and does not protect you from type mismatch. In your snipper "%d" implies that argument is address of integer variable, however you supply it address of ubyte one. As loop variable happens to be on stack right next to `tmp` variable, it gets stomped when sizeof(int) bytes get written to &tmp

Thank you everybody!!!
I thought %d is ok for all integral types.

On Wed, 16 Apr 2014 18:17:37 +0000, Capture_A_Lag wrote:

> Thank you everybody!!!
> I thought %d is ok for all integral types.

This is true when using the D format functions (e.g. readf) which are able to inspect the types of the variables being assigned, but scanf is a C function and not typesafe.

Justin

Note that readf is not equivalent to scanf since readf does not skip spaces and newline character. Input must completely match format.

On 04/16/2014 11:36 AM, FreeSlave wrote:
> Note that readf is not equivalent to scanf since readf does not skip
> spaces and newline character. Input must completely match format.

Just like in scanf, a single space character is sufficient to consume zero or more whitespace characters.

Ali