www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Input from a newbie

reply "Jonas" <jonas lophus.org> writes:
Hello D community! :-)

I was looking for a sane, object-oriented, 
possible-to-go-low-level programming language, so I decided to 
give D a try today.

Here's some feedback on the things I had/have trouble with. I 
hope some of this may be valuable for you.

1) First off, I really couldn't figure out were I was supposed to 
post this sort of message.  Apparently there aren't any mailing 
lists (a la Google groups) for D?

2) I couldn't find any good documentation on the build process 
and tools I'm supposed to use. Do you guys use standard 
Makefiles? Do you have your own build system? Would be really 
helpful if that was covered on the website.

3) While your error messages are a lot better than GCCs (gives 
you more context, hints about how the compiler interpreted your 
buggy program, etc) it wouldn't hurt if you made them a bit more 
graphical using colors and markers and such (LLVM like).

4) What's the difference between `... foo(MyObject obj) { ... }` 
and `foo(MyObject* obj)`? What are use cases for explicit 
pointers when passing objects? That's not covered in the 
documentation AFAIT.

5) What's wrong with this program? Is it that `printf` doesn't 
understand D strings? If so, how do I use D strings in string 
formatting?

import std.stdio;

string foo() { return "foobar"; }

int main() {
   printf("%s\n", foo());
   return 0;
}


Jonas
Apr 07 2012
next sibling parent reply "Stefan" <stefan schuerger.com> writes:
On Saturday, 7 April 2012 at 22:21:36 UTC, Jonas wrote:

 Hello D community! :-)

 I was looking for a sane, object-oriented, 
 possible-to-go-low-level programming language, so I decided to 
 give D a try today.


good choice, welcome! ;-)


 4) What's the difference between `... foo(MyObject obj) { ... 
 }` and `foo(MyObject* obj)`? What are use cases for explicit 
 pointers when passing objects? That's not covered in the 
 documentation AFAIT.


You normally don't need pointers. Objects are always passed by
reference. So MyObject* obj would be redundant.


 5) What's wrong with this program? Is it that `printf` doesn't 
 understand D strings? If so, how do I use D strings in string 
 formatting?

 import std.stdio;

 string foo() { return "foobar"; }

 int main() {
   printf("%s\n", foo());
   return 0;
 }


printf is a C function which expects 0-terminated strings. D's
strings are variable-length arrays and not zero-terminated.

Don't use printf. Try using writef instead. Same arguments.

Stefan
Apr 07 2012
parent reply "Jonas" <jonas lophus.org> writes:
On Saturday, 7 April 2012 at 22:42:19 UTC, Stefan wrote:

 printf is a C function which expects 0-terminated strings. D's
 strings are variable-length arrays and not zero-terminated.

 Don't use printf. Try using writef instead. Same arguments.


http://d.puremagic.com/issues/show_bug.cgi?id=7872
Apr 09 2012
next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 4/9/12, Jonas <jonas lophus.org> wrote:

 On Saturday, 7 April 2012 at 22:42:19 UTC, Stefan wrote:

 printf is a C function which expects 0-terminated strings. D's
 strings are variable-length arrays and not zero-terminated.

 Don't use printf. Try using writef instead. Same arguments.


 http://d.puremagic.com/issues/show_bug.cgi?id=7872


I don't think the compiler can warn about this. Isn't printf one of
those unsafe C variadic functions? Someone correct me if I'm wrong.
Apr 09 2012
prev sibling next sibling parent reply "Jonas H." <jonas lophus.org> writes:
On 04/09/2012 05:39 PM, Andrej Mitrovic wrote:

 I don't think the compiler can warn about this. Isn't printf one of
 those unsafe C variadic functions? Someone correct me if I'm wrong.


The GCC C compiler proves you wrong :) They have warnings. I guess it's 
a hack (because printf really doesn't belong into the compiler) but that 
doesn't matter.  What matters is user-friendliness.
Apr 09 2012
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 04/09/2012 08:50 AM, Jonas H. wrote:

 On 04/09/2012 05:39 PM, Andrej Mitrovic wrote:

 I don't think the compiler can warn about this. Isn't printf one of
 those unsafe C variadic functions? Someone correct me if I'm wrong.


 The GCC C compiler proves you wrong :) They have warnings. I guess it's
 a hack (because printf really doesn't belong into the compiler) but that
 doesn't matter. What matters is user-friendliness.


Indeed. dmd should warn about any incompatible data passed as variadic 
parameters. It's simple to decide: only fundamental types that 
correspond to C counterparts should be allowed. Hmmm... Even that's not 
that simple: int is 32 bits in D but unspecified in C.

Ali
Apr 09 2012
parent "Stefan" <stefan schuerger.com> writes:
On Monday, 9 April 2012 at 20:18:29 UTC, Ali Çehreli wrote:



 The GCC C compiler proves you wrong :) They have warnings. I 
 guess it's
 a hack (because printf really doesn't belong into the 
 compiler) but that
 doesn't matter. What matters is user-friendliness.


 Indeed. dmd should warn about any incompatible data passed as 
 variadic parameters. It's simple to decide: only fundamental 
 types that correspond to C counterparts should be allowed. 
 Hmmm... Even that's not that simple: int is 32 bits in D but 
 unspecified in C.


Maybe printf should not be visible at all - or under a different 
name ("cprintf" or something similar). It's just too tempting...

C variadic arguments are one of the most unsafe features of the C 
language. A total mess.

Stefan
Apr 09 2012
prev sibling next sibling parent Artur Skawina <art.08.09 gmail.com> writes:
On 04/09/12 17:39, Andrej Mitrovic wrote:

 On 4/9/12, Jonas <jonas lophus.org> wrote:

 On Saturday, 7 April 2012 at 22:42:19 UTC, Stefan wrote:

 printf is a C function which expects 0-terminated strings. D's
 strings are variable-length arrays and not zero-terminated.

 Don't use printf. Try using writef instead. Same arguments.


 http://d.puremagic.com/issues/show_bug.cgi?id=7872


 
 I don't think the compiler can warn about this. Isn't printf one of
 those unsafe C variadic functions? Someone correct me if I'm wrong.


It is, but arguably this is exactly why it should warn - it's unlikely
that passing a D array to an extern(C) variadic function is really what
the programmer intended. Except of course when he relies on the internal
D array representation - and, as this hack is given as an example on 
dlang.org, issuing a warning is out of the question, w/o special-casing
for printf and parsing the format string...

However, there's no reason why *std.stdio* should expose the raw printf
function - i didn't even realize it did until now...
It either shouldn't be available via std.stdio at all, or something
like this wrapper should be added there, to catch the inevitable mistakes:

int printf(string F=__FILE__, int L=__LINE__, A...)(A args) {
   import std.typetuple;
   import std.string;
   import std.c.stdio;
   alias ReplaceAll!(immutable(char)[], char*, A) CA;
   CA cargs;
   foreach (i, arg; args) {
      static if (is(typeof(arg):const(char)[])) {
         pragma(msg, F ~ ":" ~ L.stringof ~
           " Warning: C function printf expects zero-terminated (char*), not D
array");
         cargs[i] = cast(char*)toStringz(arg);
      }
      else
         cargs[i] = arg;
   }
   return std.c.stdio.printf(cargs);
}

The raw printf can then still be used via std.c.stdio or core.stdc.stdio, 
but a program using just std.stdio will print a warning instead of segfaulting.
Parsing the format string to avoid the warnings for the "%.*s" case could be
done too, i guess.


On 04/09/12 17:50, Jonas H. wrote:

 The GCC C compiler proves you wrong :) They have warnings. I guess it's a hack
(because printf really doesn't belong into the compiler) but that doesn't
matter.  What matters is user-friendliness.


D doesn't even need compiler support for this - it can be done completely
inside the library.

artur
Apr 09 2012
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 4/9/12, Artur Skawina <art.08.09 gmail.com> wrote:

 However, there's no reason why *std.stdio* should expose the raw printf
 function - i didn't even realize it did until now...
 It either shouldn't be available via std.stdio at all, or something
 like this wrapper should be added there, to catch the inevitable mistakes:


I think most mentions of printf should just be removed from the dpl
docs except maybe a few special places. People (or rather C++
refugees) seem to expect D to be a syntax sugared version of C++, but
this myth has to be busted.
Apr 09 2012
prev sibling parent "Jonas H." <jonas lophus.org> writes:
On 04/09/2012 07:22 PM, Andrej Mitrovic wrote:

 I think most mentions of printf should just be removed from the dpl
 docs except maybe a few special places. People (or rather C++
 refugees) seem to expect D to be a syntax sugared version of C++, but
 this myth has to be busted.


I don't think that's true, or at least I didn't think of D like that. 
It becomes pretty clear after reading the introduction that D does not 
try to emulate C++, let alone be compatible to C(++).

Nevertheless, because the syntax and terminology are quite similar, 
people expect stuff to have the same names. That's why I expected the 
standard printing function to be named `printf` and this attempt failed 
miserably, without any guidance from the compiler/stdlib/whatever.
Apr 09 2012
prev sibling next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Jonas:


 Hello D community! :-)


Welcome here.



 I was looking for a sane, object-oriented, 
 possible-to-go-low-level programming language, so I decided to 
 give D a try today.


D supports OOP well enough, but template-based programming seems 
equally fit or even more. Also keep in mind that the D GC is not 
so efficient, so avoid creating too many small objects, as you do 
in Java.



 1) First off, I really couldn't figure out were I was supposed 
 to post this sort of message.


This is the right place.



 2) I couldn't find any good documentation on the build process 
 and tools I'm supposed to use. Do you guys use standard 
 Makefiles? Do you have your own build system? Would be really 
 helpful if that was covered on the website.


One tool fit for not huge programs is rdmd. I use "bud" still, 
but it's getting obsolete.



 3) While your error messages are a lot better than GCCs (gives 
 you more context, hints about how the compiler interpreted your 
 buggy program, etc) it wouldn't hurt if you made them a bit 
 more graphical using colors and markers and such (LLVM like).


I don't think Walter will love this idea.



 4) What's the difference between `... foo(MyObject obj) { ... 
 }` and `foo(MyObject* obj)`?


If obj is a class instance, then the first syntax is the one you 
will find in D programs.



 What are use cases for explicit pointers when passing objects? 
 That's not covered in the documentation AFAIT.


It's not documented because you don't use explicit pointers to 
pass objects around. Pointers are used to pass structs around 
when you don't want to copy them.



 5) What's wrong with this program? Is it that `printf` doesn't 
 understand D strings? If so, how do I use D strings in string 
 formatting?


Use write, writef, writeln, writefln for D strings and for 
several other D data structures.

Take a look here for many small examples programs in D to do many 
different kind of things (not all of them are up to date or fully 
correct, but most of them are good, and the wrong ones are being 
fixed one after the other):
http://rosettacode.org/wiki/Category:D

Bye,
bearophile
Apr 07 2012
parent reply "Jonas" <jonas lophus.org> writes:
On Saturday, 7 April 2012 at 23:58:20 UTC, bearophile wrote:

 Jonas:


 Hello D community! :-)


 Welcome here.



 I was looking for a sane, object-oriented, 
 possible-to-go-low-level programming language, so I decided to 
 give D a try today.


 D supports OOP well enough, but template-based programming 
 seems equally fit or even more. Also keep in mind that the D GC 
 is not so efficient, so avoid creating too many small objects, 
 as you do in Java.



 1) First off, I really couldn't figure out were I was supposed 
 to post this sort of message.


 This is the right place.



 2) I couldn't find any good documentation on the build process 
 and tools I'm supposed to use. Do you guys use standard 
 Makefiles? Do you have your own build system? Would be really 
 helpful if that was covered on the website.


 One tool fit for not huge programs is rdmd. I use "bud" still, 
 but it's getting obsolete.



 3) While your error messages are a lot better than GCCs (gives 
 you more context, hints about how the compiler interpreted 
 your buggy program, etc) it wouldn't hurt if you made them a 
 bit more graphical using colors and markers and such (LLVM 
 like).


 I don't think Walter will love this idea.


Could you please elaborate on this a bit more? What's the problem 
with helpful compiler messages?


 What are use cases for explicit pointers when passing objects? 
 That's not covered in the documentation AFAIT.


 It's not documented because you don't use explicit pointers to 
 pass objects around. Pointers are used to pass structs around 
 when you don't want to copy them.


Thanks for the explanation!


 Take a look here for many small examples programs in D to do 
 many different kind of things (not all of them are up to date 
 or fully correct, but most of them are good, and the wrong ones 
 are being fixed one after the other):
 http://rosettacode.org/wiki/Category:D


That looks great, thanks, although it's a bit cluttered with all 
those languages ;-)
Apr 09 2012
parent "bearophile" <bearophileHUGS lycos.com> writes:
Jonas:


 Could you please elaborate on this a bit more? What's the 
 problem with helpful compiler messages?


Walter likes helpful error messages, but I think he doesn't want 
to:
1) Use too much time to improve them. There are usually more 
important problems to fix.
2) Slow down the compiler (or make it use more RAM) to generate 
better errors (this seems to happen if you want the column number 
too of the error).
3) Produce too much long error messages because he thinks most 
people are annoyed by a command line interface that gets too much 
scrolling caused by many long error messages (I think most people 
think this is a bit ridiculous justification).

But if you want to add/improve specific error messages, then ask 
for the specific improvements in D Bugzilla as enhancement 
request.



 That looks great, thanks, although it's a bit cluttered with 
 all those languages ;-)


That 'clutter' is the real purpose of that site.

If you know language X, you don't know language Y but you want to 
learn language Y, often in that site you are able to find the 
same algorithm/code implemented in both X and Y. Comparing them 
you are able to learn some Y and  the best idioms of Y too. Just 
like the true Rosetta Stone did for Egyptian language :-)

That site has other secondary purposes:
- There you often find good computer science ideas or good 
programming ideas/tricks to learn from.
- Comparing the same algorithms in many very different languages 
you are sometimes able to catch better the essence of an 
algorithm, that is what's invariant of those implementations. A 
good book that introduces to algorithms is supposed to show this 
"essence" but often it doesn't, because a book on algorithms like 
the one by Robert Sedgewick is mostly procedural, even if he has 
written books for Java, C, C++. On that site you find wildly 
different implementations based on different programming 
paradigms, like templates, pure lazy functional, dynamic 
homoiconic functional, parallel, OOP, logic programming, 
concatenative programming, stack-based, even flow programming. 
All those programming paradigms are usually absent on books like 
Robert Sedgewick ones. And often the comparison teaches you 
something. Because sometimes an algorithm or data structure must 
be changed to fit (otherwise you get things like QuickSort or the 
Sieve of Eratosthenes implemented naively in Haskell, with so bad 
performance that they essentially have become a different 
algorithm).
- If you are interested not just in algorithms (or little 
programs) and their implementations, but also in programming 
languages themselves and their design, then that site helps you 
slowly gain a broader vision of what different languages offer to 
solve specific problems, what the "taste" of a language is, what 
languages are elegant or not, what languages seem an 
agglomeration of features, what languages are practical 
"engineering products" like D or not, what type systems seem 
intrusive and what are too much rigid, and so on and on. So if 
you want you are able to use that site to learn how to design 
languages too, a bit.
- That site has several other smaller purposes.

Bye,
bearophile
Apr 09 2012
prev sibling next sibling parent "ReneSac" <reneduani yahoo.com.br> writes:
On Saturday, 7 April 2012 at 22:21:36 UTC, Jonas wrote:

 5) What's wrong with this program? Is it that `printf` doesn't 
 understand D strings? If so, how do I use D strings in string 
 formatting?

 import std.stdio;

 string foo() { return "foobar"; }

 int main() {
   printf("%s\n", foo());
   return 0;
 }


You can use toStringz() from std.string to convert D strings to 
null terminated strings when you need to interface with C 
functions. But in this case, writeln() would be the simplest 
solution. It would be only:

writeln(foo());

Instead of:

printf("%s\n", toStringz(foo()));

I'm a newbie in D too, so correct me if there is anything wrong.
Apr 07 2012
prev sibling parent reply Jonathan M Davis <jmdavisProg gmx.com> writes:
On Sunday, April 08, 2012 00:21:35 Jonas wrote:

 1) First off, I really couldn't figure out were I was supposed to
 post this sort of message.  Apparently there aren't any mailing
 lists (a la Google groups) for D?


These are both newsgroups and mailing lists, and there's forum software on top 
of it as well.

Newsgroups: http://www.digitalmars.com/NewsGroup.html
Mailing Lists: http://lists.puremagic.com/cgi-bin/mailman/listinfo
Forum: http://forum.dlang.org/

You can pick which interface you want to use. They're all the same thing. It's 
just a question of how you access it. But no, it's not quite like google 
groups.

- Jonathan M Davis
Apr 07 2012
parent "Jonas" <jonas lophus.org> writes:
On Sunday, 8 April 2012 at 03:55:33 UTC, Jonathan M Davis wrote:

 On Sunday, April 08, 2012 00:21:35 Jonas wrote:

 1) First off, I really couldn't figure out were I was supposed 
 to
 post this sort of message.  Apparently there aren't any mailing
 lists (a la Google groups) for D?


 These are both newsgroups and mailing lists, and there's forum 
 software on top
 of it as well.

 Newsgroups: http://www.digitalmars.com/NewsGroup.html
 Mailing Lists: 
 http://lists.puremagic.com/cgi-bin/mailman/listinfo
 Forum: http://forum.dlang.org/

 You can pick which interface you want to use. They're all the 
 same thing. It's
 just a question of how you access it. But no, it's not quite 
 like google
 groups.


Thanks Jonathan, the mailman interface is what I looked for.
Apr 09 2012