[marrymehyori]

I'm having a hell of a time figuring out how to make the multiset class work with an object. Every single example I find uses int, nothing showing how it works with an object. I'm totally stumped

I mean I can't even get my program to compile, and I don't quite understand these compiler errors. I've always had trouble with STL

[angelqian]

multiset<object> blah = new multiset()... something like that.

but this is the wrong forum for that kinda stuff... com'n, we're all about kpop right?

[watcher]

what are you trying to do, and what's the error you're getting?
multisets are the same as sets, except that you can have duplicate entries.
btw...
hyori is mine!

[marrymehyori]

I think I got the creation of the set down ok - I'm at the point where I need to iterate over the objects in the set.

int main(void)
{
typedef multiset<foo, foo_sort> FooSet;

FooSet foo_set;

for (int i = 0; i < 10; i++) {
foo obj;
obj.fubar = i;
foo_set.insert(obj);
}


foo bar;
list<foo>::iterator it;
for (it = foo_set.begin(); it != foo_set.end(); it++) {
bar = foo(*it);
cout << bar.fubar << endl;
}

return 0;
}


This doesn't compile (line numbers are off as I haven't included the class definition):

$ g++ -g -Wall test.cpp
test.cpp: In function `int main()':
test.cpp:94: error: no match for 'operator=' in 'it = (&foo_set)->std::multiset<_Key, _Compare, _Alloc>::begin [with _Key = foo, _Compare = foo_sort, _Alloc = std::allocator<foo>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/bits/stl_list.h:112: note: candidates are: std::_List_iterator<foo>& std::_List_iterator<foo>::operator=(const std::_List_iterator<foo>&)
test.cpp:94: error: no match for 'operator!=' in 'it != (&foo_set)->std::multiset<_Key, _Compare, _Alloc>::end [with _Key = foo, _Compare = foo_sort, _Alloc = std::allocator<foo>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../../include/c++/3.4.6/bits/stl_list.h:173: note: candidates are: bool std::_List_iterator<_Tp>::operator!=(const std::_List_iterator<_Tp>&) const [with _Tp = foo]


eh... say what? My 'foo' class does indeed have operator= and operator!= overloaded, so I'm not sure what the problem is. Surely they don't expect me to overload those operators on the multiset or list class?

[marrymehyori]

Nevermind, I got it. 'FooSet::iterator it' instead of 'list<foo>::iterator it'

[marrymehyori]

Now apparently I need a lesson in how STL's find function works... As best I can figure out, it uses the < operator? But just to be safe, I defined all the comparison operators for my object.

class phone_data_struct {
public:
char cid[18];

...

bool operator <(const phone_data_struct &rhs) const {
return (strncmp(cid, rhs.cid, sizeof(cid)) < 0 ? true : false);
}

bool operator <=(const phone_data_struct &rhs) const {
return (strncmp(cid, rhs.cid, sizeof(cid)) <= 0 ? true : false);
}

bool operator==(const phone_data_struct &rhs) const {
return (strncmp(cid, rhs.cid, sizeof(cid)) == 0 ? true : false);
}

// etc. for the rest of the comparison operators

};

class phone_sort {
public:
bool operator() (const phone_data_struct &a, const phone_data_struct &b) const {
return (strncmp(a.cid, b.cid, sizeof(a.cid)));
}
};


int main(void)
{
typedef multiset<phone_data_struct, phone_sort> PhoneSet;
PhoneSet phone_data_list;

// Skip code that populates the set

phone_data_struct dummy(cur_trig.cid, " ", ' ');
PhoneSet::iterator itp = phone_data_list.find(dummy);


This NEVER finds a match. I looked in gdb and saw that the cur_trig.cid did indeed match the cid in at least one of the nodes of phone_data_list, so it SHOULD be returning SOMETHING, but it doesn't. Does it use something other than the operators I defined for phone_data_struct? Does it attempt to determine equality based on ALL the member variables or some other criteria? I'm so confused