Hello all!

Is
	writefln( (i<10?" ":"") ~ "%d: %s", i, v);

supposed to work, according to the specs?
Just looked at them, but couldn't quiet get it.

But nevertheless it *does* work,
no compile/runtime error and it acts
also in the expected way.

BUT: I just came back from hunting (bugs),
and you get an error if you write the above code
in a file, read it in using std.file & std.stream,
and writefln it back to the console:

*** bugtest.txt
writefln( (i<10?" ":"") ~ "%d: %s", i, v);

*** bugtest.d
import std.file, std.stream, std.stdio;
void main()
{
	File file = new File;
	file.open("bugtest.txt");
	char[] line;
	line = file.readLine();
	file.close();
	writefln(line);		// here we get an error
}


david

david schrieb:
> Hello all!
> 
> Is
>     writefln( (i<10?" ":"") ~ "%d: %s", i, v);
> 
> supposed to work, according to the specs?
> Just looked at them, but couldn't quiet get it.
> 
> But nevertheless it *does* work,
> no compile/runtime error and it acts
> also in the expected way.
> 
> BUT: I just came back from hunting (bugs),
> and you get an error if you write the above code
> in a file, read it in using std.file & std.stream,
> and writefln it back to the console:
> 
> *** bugtest.txt
> writefln( (i<10?" ":"") ~ "%d: %s", i, v);
> 
> *** bugtest.d
> import std.file, std.stream, std.stdio;
> void main()
> {
>     File file = new File;
>     file.open("bugtest.txt");
>     char[] line;
>     line = file.readLine();
>     file.close();
>     writefln(line);        // here we get an error
> }
> 
> 
> david

Just confirmed:
*** bug.d
import std.stdio;
void main()
{
	char[] line;
	line = "writefln( (i<10?\" \":\"\") ~ \"%d: %s\", i, v);";
	writefln(line);		// here we get an error
}

It compiles just fine, so the string should be ok, BUT at runtime:
Error: std.formatwritefln( (i<10?" ":"") ~ "

david

david wrote:
> Hello all!
> 
> Is
>     writefln( (i<10?" ":"") ~ "%d: %s", i, v);
> 
> supposed to work, according to the specs?
> Just looked at them, but couldn't quiet get it.

Yes, that should be fine (assuming i is some form of integer).

> But nevertheless it *does* work,
> no compile/runtime error and it acts
> also in the expected way.
> 
> BUT: I just came back from hunting (bugs),
> and you get an error if you write the above code
> in a file, read it in using std.file & std.stream,
> and writefln it back to the console:
> 
> *** bugtest.txt
> writefln( (i<10?" ":"") ~ "%d: %s", i, v);
> 
> *** bugtest.d
> import std.file, std.stream, std.stdio;
> void main()
> {
>     File file = new File;
>     file.open("bugtest.txt");
>     char[] line;
>     line = file.readLine();
>     file.close();
>     writefln(line);        // here we get an error
> }

That's a different matter entirely. String arguments to writef and friends are by default treated as format strings. Since the string you provide contains %d and %s, it expects two additional arguments. Since none are provided it throws an exception. Change the last line to
---
    writefln("%s", line);
---
to write out the exact contents of the string.

Stuff like this is why we *really* need non-formatting write functions :(...

Frits van Bommel schrieb:
> david wrote:
>> Hello all!
>>
>> Is
>>     writefln( (i<10?" ":"") ~ "%d: %s", i, v);
>>
>> supposed to work, according to the specs?
>> Just looked at them, but couldn't quiet get it.
> 
> Yes, that should be fine (assuming i is some form of integer).
> 
>> But nevertheless it *does* work,
>> no compile/runtime error and it acts
>> also in the expected way.
>>
>> BUT: I just came back from hunting (bugs),
>> and you get an error if you write the above code
>> in a file, read it in using std.file & std.stream,
>> and writefln it back to the console:
>>
>> *** bugtest.txt
>> writefln( (i<10?" ":"") ~ "%d: %s", i, v);
>>
>> *** bugtest.d
>> import std.file, std.stream, std.stdio;
>> void main()
>> {
>>     File file = new File;
>>     file.open("bugtest.txt");
>>     char[] line;
>>     line = file.readLine();
>>     file.close();
>>     writefln(line);        // here we get an error
>> }
> 
> That's a different matter entirely. String arguments to writef and friends are by default treated as format strings. Since the string you provide contains %d and %s, it expects two additional arguments. Since none are provided it throws an exception. Change the last line to
> ---
>     writefln("%s", line);
> ---
> to write out the exact contents of the string.
> 
> Stuff like this is why we *really* need non-formatting write functions :(...

Thanks a lot for the explanation, now it is clear (and works).
Althoug I guess this could pose a risk for bugs in other people's code,
since the code itself works and the bug only pops up on very special
input data occasions. (glad I'm enlightened now ^_^)

david