Re: To go with Go or C/C++?
On Monday, May 13, 2013 9:02:38 AM UTC+1, David Brown wrote:
On 12/05/13 00:39, Ian Collins wrote:
James Kanze wrote:
On Friday, May 10, 2013 6:09:27 PM UTC+1, Scott Lurndal wrote:
Paavo Helde <myfirstname@osa.pri.ee> writes:
[...]
Since most of my programming is on linux, I use gcc's
__attribute__((printf,...)) to let the compiler ensure
type-safety,
Except that this feature doesn't work, since you almost never
have format strings that are compile time constants.
It also appears unnecessary due to gcc doing the type checking by
default.
That's because the libraries for gcc already have the "printf" attribute
in their declarations for things like printf, snprintf, etc. So you
only need the attribute if you are making your own printf-like functions.
I don't buy the "never have format strings that are compile
time constants" part however. Just about everywhere I've seen (s)printf
used has been with a fixed format string.
I agree with that in most cases. And the C++ standard alternative -
using << and >> - fixes the formatting in compile-time code.
Not any more than standard printf.
Unix extends it to allow changes in order. Back when I started
C++, I implemented something similar in a type safe manner, with
full support of _all_ of the printf formatting options. It
turned out to be useless. By the time you have to start
worrying about word order, you're also having to deal with
things like agreement (where adjectives have to agree in number,
gender, and possibly case with the noun they modify) and other
more complicated issues. If you need variations in word order,
you probably need a separate DLL for each language, to handle
the grammatical issues.
One common situation where the format strings are non-constant is with
internationalised code, such as using gettext. Then you have things like:
printf(_("The date is %02d/%0d\n"), day, month);
gcc can't do static checking on this as it stands - but it's easy enough
to add some pre-processor magic so that you can do a "check" compile
with _() defined to nothing.
And you can do things like add an American translation of the string as
"The American-style date is %2$02d/%1$02d\n" - something that cannot be
achieved with << and >>.
Not with standard printf. That's a Unix (not even Posix)
extension. And from experience: it doesn't work. (The case of
dates is particularly special: there are a number of
conventions, which don't respect the usual locales---US military
uses a different format than civilian use, etc. The best
solution here is to correctly overload
operator<<( std::ostream&, Date const& ) to do the right thing,
picking up the format from a user defined manipulator, and
things like the names of months from an external file. Or just
to use ISO format everywhere, but the world isn't ready for that
yet.)
There are times that << and >> are useful too - but printf and friends
are still often the best choice.
I can definitely think of cases where there could be better
solutions than << and >>. But none where printf would be that
solution.
--
James