Hey all,

I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.

Given the following code:

---- test.d ----

import std.stdio, std.algorithm, std.conv, std.format, std.string;

void main() {
  int x;
  for (auto t = 40; t < 50; t++) {
    // Create a string holding a number and put a forward slash behind it
    string l = to!string(t) ~ "/";

    // Write the created string to the ouput
    writef("'%s'", l);

    // Read the number using the formattedRead function
    formattedRead(l, "%d", &x);

    // Write the number to the ouput
    writef(" -> '%d'", x);

    // Skip over the loaded number
    l.skipOver(x);

    // Print what is left of the string
    writeln(" -> '", l, "'");
  }
}
-------------------

After running this code  dmd -run test.d
I get the following output:

'40/' -> '40' -> '/'
'41/' -> '41' -> '/'
'42/' -> '42' -> '/'
'43/' -> '43' -> '/'
'44/' -> '44' -> '/'
'45/' -> '45' -> '/'
'46/' -> '46' -> '/'
'47/' -> '47' -> ''
'48/' -> '48' -> '/'
'49/' -> '49' -> '/'

Why is in the case of 47, the slash at the end eaten up by the skipOver function ?
I tested all numbers from 0 to 1000, and it only occurs when the number is 47 (?!)

Can anyone confirm this, since it looks like such a weird bug to me ?

Kind regards,
Danny Arends

On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
> Hey all,
>
> Can anyone confirm this, since it looks like such a weird bug to me ?
>
> Kind regards,
> Danny Arends

The ASCII code for / is 47.

On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
> Hey all,
>
> I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.
>
> [...]

Two further observations:

(Obs 1)

47 is ascii code for forwards slash '/'

(Obs 2)

Changing the line:

l.skipOver(x);

to:

l.skipOver(to!string(x));

Does not show the bug.

On Sunday, 22 January 2017 at 10:01:09 UTC, Danny Arends wrote:
> On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
>> Hey all,
>>
>> I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.
>>
>> [...]
>
> Two further observations:
>
> (Obs 1)
>
> 47 is ascii code for forwards slash '/'
>
> (Obs 2)
>
> Changing the line:
>
> l.skipOver(x);
>
> to:
>
> l.skipOver(to!string(x));
>
> Does not show the bug.

This is not a bug.
But working as intended.
you call skip over with an (char[] skip, int overThis)
and skip over will do comparions like this (if (skip[pos] == overThis))
and since '\' == 47;
it will skip over that one.

On Sunday, 22 January 2017 at 10:30:14 UTC, Stefan Koch wrote:
> On Sunday, 22 January 2017 at 10:01:09 UTC, Danny Arends wrote:
>> On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
>>> Hey all,
>>>
>>> I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.
>>>
>>> [...]
>>
>> Two further observations:
>>
>> (Obs 1)
>>
>> 47 is ascii code for forwards slash '/'
>>
>> (Obs 2)
>>
>> Changing the line:
>>
>> l.skipOver(x);
>>
>> to:
>>
>> l.skipOver(to!string(x));
>>
>> Does not show the bug.
>
> This is not a bug.
> But working as intended.
> you call skip over with an (char[] skip, int overThis)
> and skip over will do comparions like this (if (skip[pos] == overThis))
> and since '\' == 47;
> it will skip over that one.

Yeah I kind of figured that, however it is very confusing the skipOver() function, first tries to match an integer input as a ascii code.

However if this ascii code is NOT found (e.g. when x = 46, ascii code for '.') it promotes the integer to a string, and then skips passed the string 46.

I think the promotion of the input integer to string shouldn't happen, or should be clearly documented..

Greetings
Danny

On Sunday, 22 January 2017 at 11:20:18 UTC, Danny Arends wrote:
> On Sunday, 22 January 2017 at 10:30:14 UTC, Stefan Koch wrote:
>> On Sunday, 22 January 2017 at 10:01:09 UTC, Danny Arends wrote:
>>> On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
>>>> Hey all,
>>>>
>>>> I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.
>>>>
>>>> [...]
>>>
>>> Two further observations:
>>>
>>> (Obs 1)
>>>
>>> 47 is ascii code for forwards slash '/'
>>>
>>> (Obs 2)
>>>
>>> Changing the line:
>>>
>>> l.skipOver(x);
>>>
>>> to:
>>>
>>> l.skipOver(to!string(x));
>>>
>>> Does not show the bug.
>>
>> This is not a bug.
>> But working as intended.
>> you call skip over with an (char[] skip, int overThis)
>> and skip over will do comparions like this (if (skip[pos] == overThis))
>> and since '\' == 47;
>> it will skip over that one.
>
> Yeah I kind of figured that, however it is very confusing the skipOver() function, first tries to match an integer input as a ascii code.
>
> However if this ascii code is NOT found (e.g. when x = 46, ascii code for '.') it promotes the integer to a string, and then skips passed the string 46.
>
> I think the promotion of the input integer to string shouldn't happen, or should be clearly documented..
>
> Greetings
> Danny

No it never promotes the integer to a string.
it compares a char to an uint.
You pass a string and an int to it.
And the elements of the string are getting compared to the uint
See this overload
https://dlang.org/phobos/std_algorithm_searching.html#.skipOver.2

Add a `writeln(l);` after the call to formattedRead().

On Sunday, 22 January 2017 at 11:20:18 UTC, Danny Arends wrote:
> On Sunday, 22 January 2017 at 10:30:14 UTC, Stefan Koch wrote:
>> On Sunday, 22 January 2017 at 10:01:09 UTC, Danny Arends wrote:
>>> On Sunday, 22 January 2017 at 09:55:49 UTC, Danny Arends wrote:
>>>> Hey all,
>>>>
>>>> I encountered some unexpected behavior in std.format, I was parsing Wavefront obj file, and ran into an issue. I updated the compiler to the latest stable version (// DMD64 D Compiler v2.072.2), however I think it's a Phobos related issue.
>>>>
>>>> [...]
>>>
>>> Two further observations:
>>>
>>> (Obs 1)
>>>
>>> 47 is ascii code for forwards slash '/'
>>>
>>> (Obs 2)
>>>
>>> Changing the line:
>>>
>>> l.skipOver(x);
>>>
>>> to:
>>>
>>> l.skipOver(to!string(x));
>>>
>>> Does not show the bug.
>>
>> This is not a bug.
>> But working as intended.
>> you call skip over with an (char[] skip, int overThis)
>> and skip over will do comparions like this (if (skip[pos] == overThis))
>> and since '\' == 47;
>> it will skip over that one.
>
> Yeah I kind of figured that, however it is very confusing the skipOver() function, first tries to match an integer input as a ascii code.
>
> However if this ascii code is NOT found (e.g. when x = 46, ascii code for '.') it promotes the integer to a string, and then skips passed the string 46.
>
> I think the promotion of the input integer to string shouldn't happen, or should be clearly documented..
>
> Greetings
> Danny

It really isn't if you understand how the types are operating when compiled. There is theoretically no such thing as a character when it comes to actual data types. It's nothing but a number on the OS level. Unless it's a Unicode etc. then it's a sequence of numbers to form code points