Question

I have a class which has a map. I need to find iterator in map by searching for a particualar value, instad of the key. Using a member function predicate IsValueFound, am trying this.

class A
{
public:
  void findVal();
private:
 int state;
 map<int, int> exmap;
 bool IsValueFound(pair<int key, int val> itr)
 {
   return state == itr.second;
 }
};

void A::findVal
{
  itr = find_if(exmap.begin, exmap.end, mem_fun1_ref(&A::IsValueFound));
}

Iam getting compilation errors. Iam not sure whats the syntax for these function adaptors. Please help.

EDIT: Sorry. Please neglect the compilation errors arising other than from finf_if stmt. I need to get find_if stmt corrected first. Also the code doesn’t have boost 🙁

Answer 1

Edit: there’s obviously an error in my answer, mem_fun1_ref(&A::IsValueFound) doesn’t work as a predicate for std::find_if. I’m working on correcting that.

you forgot parenthesis with exmap.begin and exmap.end.
I think if you had read the compilation error report, it would have told seomthing about it.

I would write that this way:

typedef map<int, int>::const_iterator MyIterator
void A::findVal()
{
    const MyIterator itrBegin = exmap.begin();
    const MyIterator itrEnd = exmap.end();
    MyIterator itrFound = find_if( itrBegin ,
                                   itrEnd ,
                                   mem_fun1_ref(&A::IsValueFound));    
}

but I havent’t tried mem_fun1_ref(&A::IsValueFound) to compile. and I’m not used to using mem_fun1_ref, I always redefine my own functor with their operator().