Re: [Boost-users] Unknown program_options bomb

From: Will Bryant (will_at_[hidden])
Date: 2005-11-20 20:56:13

Merrill Cornish wrote:
> I am using Boost 1.33.0 with MinGW on Windows XP.  I am using the following program_optins code to collect command line arguments:
>   
[snip]
>     * vm.count("graph_file") returns 0 regardless of whether there are positional argument(s).
>
>     * specifying an -x, --xx, --xx=n option where "x" or "xx" is not included in desc.add_options() causes store() to not return (the program simply stops).
>
> Am I missing something?
>   
As Liam points out, you need to use command_line_parser and 
positional(...), which should resolve the first problem.

However, I've just hit the second problem in my own program, the help 
formatter function is barfing.  I'm using Visual Studio 2005 (still on 
beta 2) on Windows XP and in fact I would have assumed this crash was a 
bug in the beta, but if you're seeing similar crashage under MinGW too 
then that seems unlikely. 

Running it under the debugger shows an assertion failure in the string 
iterator's += overloading, which is called by the -= overloading, which 
is called by format_paragraph (line 377 in boost 1.33's 
options_description.cpp):
                        string::const_iterator last_space =
                            
find(reverse_iterator<string::const_iterator>(line_end - 1),
                                 
reverse_iterator<string::const_iterator>(line_begin - 1),
                                 ' ')
                            .base();

(What's the deal with the reverse_iterator<string::const_iterator>s 
there, is string::const_reverse_iterator nonstandard or unreliable?)

Looking at the options_description code, I believe the offending 
calculation is "line_begin-1", which isn't valid since on the first 
iteration line_begin will normally be equal to par.begin() (and so will 
typically only work on string implementations where iterators are 
pointers). 

In other words, it appears to be an off-by-one bug in the iterator 
constructions in format_paragraph.

Cheers,
Will

-- 
Will Bryant
http://carcino.gen.nz/
will_at_[hidden]
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