[Boost-users] [program_options] setting defaults

From: Liam Routt (caligari_at_[hidden])
Date: 2005-03-14 19:37:56

Part one:

I spent yesterday trying to use a char * to set the default for a 
string option:

   opts.add_option("config", "Set the config file to examine",
                     po::value<string>()->default_value("newconfig"));

The result was a segmentation fault or illegal instruction during the 
destruction of my opts class (a wrapper that has several 
options_descriptions and a positional_options_description; there are 
methods like the add_option() above that allow various options to be 
set, in general they put the value_semantic argument last, but otherwise 
pass arguments directly through).

So today I realized that passing a char * to something expecting a 
std:string might be asking for trouble. So I tried this:

   string DefaultConfig("newconfig");
   opts.add_option("config", "Set the config file to examine",
                     po::value<string>()->default_value(DefaultConfig));

That didn't work any better. Moving the string to global scope didn't 
help, nor did making it static.

So, how do I set the default for a string option?

Part two:

I want to set up a boolean option (its existence returns true, and if it 
is not there it returns false). This is done using bool_switch(), I see. 
However I end up with a segmentation fault if I use this following line:

   opts.add_option("bool", "testing boolean", po::bool_switch());

The fault occurs, again, when opts' destructor is running. If I leave 
out the bool_switch() (ie. don't set a value semantic) I get no such 
error, although the behaviour is not as I'd like it.

So, how do I use bool_switch()?

What am I missing here? It is possible I'm having trouble with all 
occurences of po::value<>, as I haven't used it elsewhere yet (I'm 
adding stuff gradually)...

Take care,

Liam
--
Liam Routt                                          Ph: [phone]
Research Programmer                               caligari_at_[hidden]
Computer Science, Melbourne University              (or liam_at_[hidden])