Question

map<string,string>::find seems to be returning garbage iterator, since i can access neither my_it->first nor second (NB: my_it != my_map.end() is verified). VC2010 reports a debug error, and looking deeper reveals

my_it is (Bad Ptr, Bad Ptr).

The ‘offending’ map is a class attribute, _match, shown below in context:

class NicePCREMatch
{
private:
    map<string, string, less<string> > _match;

public:
    void addGroup(const string& group_name, const string& value);
    string group(const string& group_name);
};

Here is the code that returns elements by key (the commented-out code works fine):

string NicePCREMatch::group(const string& group_name)
{
    /*for (map<string, string, less<string> >::iterator j = _match.begin(); j != _match.end(); j++)
    {
        if(!strcmp(j->first.c_str(), group_name.c_str()))
        {
            return j->second;
        }
    }

    throw runtime_error("runtime_error: no such group");*/

    map<string, string, less<string> >::iterator i = _match.find(group_name);

    if (i == _match.end())
    {
        throw runtime_error("runtime_error: no such group");
    }

    return i->second;
}

And Here is the code that inserts new elements in the map:

void NicePCREMatch::addGroup(const string& group_name, const string& value)
{
    _match.insert(pair<string, string>(group_name, value));
}

Another class uses NicePCREMatch as follows:

template<class Match_t>
vector<Match_t> NicePCRE<Match_t>::match(const string& buf)
{
[snip]
    Match_t m;
[snip]
    m.addGroup(std::string((const char *)tabptr + 2, name_entry_size - 3), \
                buf.substr(ovector[2*n], ovector[2*n+1] - ovector[2*n]));
[snip]
    addMatch(m);
[snip]
    return _matches;
}

Where,

template<class Match_t>
void NicePCRE<Match_t>::addMatch(const Match_t& m) 
{ 
    _matches.push_back(m);
}

Finally, client code uses NicePCRE class as follows:

void test_NicePCRE_email_match(void)
{
    NicePCRE<> npcre;
    npcre.compile("(?P<username>[a-zA-Z]+?)(?:%40|@)(?P<domain>[a-zA-Z]+\.[a-zA-Z]{2,6})");
    vector<NicePCREMatch> matches = npcre.match("[e-mail]");
    assert(!matches.empty());
    assert(!strcmp(matches.begin()->group("username").c_str(), "toto"));
    cout << matches.begin()->group("domain").c_str() << endl;
    assert(!strcmp(matches.begin()->group("domain").c_str(), "yahoo.com"));
}

BTW, this –is pretty much– my main (the oddest TDD ever 🙂 ):

int main()
{
    int test_cnt = 0;
    cout << "Running test #" << test_cnt << " .." << endl;
    test_NicePCRE_email_match();
    cout << "OK." << endl << endl;
    test_cnt++;

    SleepEx(5000, 1);

    return 0;
}

What am I doing wrong here?

EDIT:
The following modification (compare with the version above) solved my problem. Viz,

void NicePCREMatch::addGroup(const string& group_name, const string& value)
{
    _match.insert(pair<string, string>(group_name.c_str(), value.c_str()));
}

Client code (slightly modified) now looks like this:

void test_NicePCRE_email_match(void)
{
    NicePCRE<> npcre;
    npcre.compile("(?P<username>[a-zA-Z]+?)(?:%40|@)(?P<domain>[a-zA-Z]+\.[a-zA-Z]{2,6})");
    vector<NicePCREMatch> matches = npcre.match("[e-mail]");
    assert(!matches.empty());
    try
    {
        assert(!strcmp(matches.begin()->group("username").c_str(), "toto"));
        assert(!strcmp(matches.begin()->group("domain").c_str(), "yahoo.com"));
        cout << "username = " << matches.begin()->group("username") << endl;
        cout << "domain = " << matches.begin()->group("domain") << endl;
    }
    catch (const runtime_error& e)
    {
        cout << "Caught: " << e.what() << endl;
        assert(0x0);
    }
}

This is quite bizarre. Can someone please explain. However, I consider my problem solved already.

Thanks every one.

Answer 1

Your issue is here

if (i == _match.end())
{
    throw runtime_error("runtime_error: no such group");
}

return i->second;

Your find failed for some reason. I can’t say why because I don’t have the full code. But, after the failure, you are throwing an error, but there is nobody to catch outside. Please add a try catch at the point where you call the method group() and implement the logic if the match is not found.
I tried with your sample snippets (+ some changes to get the stuff compiled) and it looks like visual studio continues with the next line in the function even after a throw statement. I don’t know the theory behind it. I was bit surprised at seeing such a behavior.

[To make sure that your class structure is not causing the problem, I tried with a simple global method and even the method also gave me the same behavior. If there are somebody who can explain this please feel free.]