Re: [Boost-users] Access violation in Boost.Format usingabsolutetabulations

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2006-05-24 03:50:06

Edson Tadeu ha escrito:

> If the format string have an absolute tabulation (%t), the
> basic_format::clear()
> method throws an access violation because of this piece code in
> format_implementation.hpp(138):
>
>             if( bound_.size()==0 || !bound_[ items_[i].argN_ ] )
>
> Here items_[i].argN_ can be negative (defined in internals.hpp(70)),
> which
> is an invalid index to bound_[].
> I think a simple check of greather than zero would suffice to fix it.
> Here is a code that catches it:
>
> using boost::format;
> format f("%0s%-32.32s:%|40t|%|.6|%|55t|%25s\n");
> f % "test1" % 2.0 % "test3";
> f % "test4" % 5.0 % "test6"; // calls clear() and breaks

Hello Edson,

The test case you propose doesn't call clear() nor shows the error
you refer to: instead, a boost::io::too_many_args is thrown. Am I
missing something?

Anyway, seems like you spotted a real problem, and the following
does actually call bound_[ items_[i].argN_ ] with items_[i].argN_
negative inside basic_format::clear(), at least for the Boost.Format
code in the CVS trunk:

    format f("%40t%1%");
    int x=0;
    f.bind_arg(1,x);
    f.clear();

Can you also observe a crash with this snippet? If so, I can try to
propose and commit a fix following your suggestion of adding
a positiveness check in the offending if.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo