Re: boost::variant and VC debugger

"giancarp" <>
19 May 2006 04:52:49 -0700
Thanks a lot for your help... As Jeff wrote, casting in the watch
window doesn't work. And even looking at the buffer itself, the data is
not easily readable.

One of the suggestions was that the debugger can evaluate some standard
functions so I decided to try a simple function that takes in input a
boost::variant and calls internally the boost::apply_visitor() method.

This solution seems to work ok-ish from the command window, even if the
watch window seems to evaluate the function only once (instead of
calling it again every time the object is modified). Which forces me to
use the command line to examine the value for the boost::variant.

Basically what i did was something on the lines:

typedef boost::variant<long, std::string> GcVariant;

class GcString: public boost::static_visitor<string>{
    string operator()(long i) const {
        stringstream istr;
        istr << i;
        return istr.str();

    string operator()( const string& i) const {
        return i;

const char* SV( const GcVariant& p_variant) {
    static string outputString;
    outputString = boost::apply_visitor( GcString(), p_variant );
    return outputString.c_str();

And if in the code i defined say:
GcVariant u;
u = "This is a string";
u = 234;
I can use the command window and type SV(u) and see the values "This is
a string" and "234".

One more question about the debugger ... if i define the function:
const std::string returnString() { return std::string("Test string"); }
and i try to evaluate it using the debugger i get a <Bad Ptr>. Does
this sound normal?

(this is the reason why i declare a static string in SV() and return
the c_str() that seems correctly handled by the debugger)
Thanks for your help!

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