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March 04, 2011
Needing to match white space during formatted read
I am asking this question from the point of view of someone who is in 
the process of replacing std.cstream with std.stdio in his book that 
targets novices. There are many sample programs in the book where the 
user interacts with the program through the console.

I would like to know whether the changes that I will be making will be 
correct.

import std.stdio;

void main()
{
    int i;
    int j;

    readf("%d%d", &i, &j);
}

1) The code above does not terminate when I interact with the program at 
the console and enter "1 2" from the keyboard (without the double quotes)

I understand that the reason is the space character that I had to type 
between the two values. The solution is to use a format string that must 
take account for that white space.

Does that mean that we must always use spaces before format specifiers 
as in " %d %d" (and even better: " %s %s")?

2) The equivalent C program does not require a space between format 
specifiers. Is this departure from C intentional?

#include <stdio.h>

int main()
{
    int i = 0;
    int j = 0;

    scanf("%d%d", &i, &j);
}

I think D is more consistent here, but the difference in behavior is 
non-trivial.

3) The program above behaves differently when the input is piped from 
the output of another program:

$ echo '1 2' | ~/deneme/d/deneme
std.conv.ConvException@std/conv.d(37): std.conv(1161): Can't convert 
value ` 2
' of type LockingTextReader to type int
----------------

That probably needs a bug report but where do you think the difference 
originates from: keyboard, echo, console, D runtime, Phobos, something else?

Thank you,
Ali
March 08, 2011
Re: Needing to match white space during formatted read
On 03/04/2011 11:21 AM, Ali Çehreli wrote:
> I am asking this question from the point of view of someone who is in
> the process of replacing std.cstream with std.stdio in his book that
> targets novices. There are many sample programs in the book where the
> user interacts with the program through the console.

Console interaction is for novices. There are no novices here.

> I would like to know whether the changes that I will be making will be
> correct.

Just make them correctly.

> import std.stdio;
>
> void main()
> {
> int i;
> int j;
>
> readf("%d%d", &i, &j);
> }
>
> 1) The code above does not terminate when I interact with the program at
> the console and enter "1 2" from the keyboard (without the double quotes)
>
> I understand that the reason is the space character that I had to type
> between the two values. The solution is to use a format string that must
> take account for that white space.
>
> Does that mean that we must always use spaces before format specifiers
> as in " %d %d" (and even better: " %s %s")?

That's sounds right.

> 2) The equivalent C program does not require a space between format
> specifiers. Is this departure from C intentional?

Forget C. Do D.

> 3) The program above behaves differently when the input is piped from
> the output of another program:
>
> $ echo '1 2' | ~/deneme/d/deneme
> std.conv.ConvException@std/conv.d(37): std.conv(1161): Can't convert
> value ` 2
> ' of type LockingTextReader to type int
> ----------------

Then just don't pipe.

> That probably needs a bug report but where do you think the difference
> originates from: keyboard, echo, console, D runtime, Phobos, something
> else?

Please file a bug report.

> Thank you,
> Ali

Thank me,
Ali
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