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digitalmars.D.learn - hackish writefln? and

reply david <ta-nospam-zz gmx.at> writes:
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
Apr 28 2007
next sibling parent david <ta-nospam-zz gmx.at> writes:
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
Apr 28 2007
prev sibling parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
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 :(...
Apr 28 2007
parent david <ta-nospam-zz gmx.at> writes:
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
Apr 28 2007