# FBB::PtrIter(3bobcat)

## Iterator pointing to pointers
(libbobcat-dev_6.14.00)

## 2005-2026

## NAME

FBB::PtrIter - Iterator returning pointer when dereferenced

## SYNOPSIS

#include <bobcat/ptriter>

## DESCRIPTION

The PtrIter class template implements an input iterator whose operator* returns the address of the element the iterator refers to. Consider a std::unordered_map<std::string, DataType>. Its begin member returns an iterator whose operator* returns a std::pair<std::string, DataType> (const) &. This is usually what you want, but now assume we want to display the map's content, sorted by its keys. Sorting can simply be performed by defining a support vector containing pointers to the elements in the map, and then sorting the strings the pointers point at.

PtrIter is a tool that can be used to construct such a support vector, as shown in the EXAMPLE section.

PtrIter is a class template requiring one template type parameter: Iterator, the iterator's type (e.g., vector<string>::iterator)

PtrIter's users don't have to specify PtrIter's template type. The function template ptrIter, when provided with an iterator returns the matching PtrIter object.

## NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

## INHERITS FROM

std::iterator<std::input_iterator_tag, ...>

## FREE FUNCTION

- PtrIter<Iterator> ptrIter(Iterator const &iter):
  this function template returns a PtrIter object for the function's Iterator argument. This function template simplyfies the construction of a PtrIter as no template parameters need to be specified (see also the EXAMPLE section)

## CONSTRUCTORS

- PtrIter(Iterator const &iter):
  The iter parameter must be initialized with an existing input iterator, offering operator*, operator++, operator== and operator!=. As PtrIter is a class template, its template type parameters must be specified when defining a PtrIter object. E.g.,

          PtrIter<set<string>::iterator> PtrIter(mySet.begin());

Copy and move constructors (and assignment operators) are available.

## OVERLOADED OPERATORS

- PtrType operator*() const:
  the address of the entity the iterator refers to is returned;
- PtrIter &operator++():
  the iterator is (pre)incremented to the next position;
- bool operator==(PtrIter const &other) const:
  true is returned if the two iterators are equal;
- bool operator!=(PtrIter const &other) const:
  true is returned if the two iterators are unequal;

## USING DECLARATION

The PtrIter class template defines PtrType:

- using PtrType = decltype(&*Iterator()):

## MEMBER FUNCTIONS

All members of std::iterator<std:::input_iterator_tag, ...> are available, as FBB::PtrIter inherits from this class.

## EXAMPLE

    #include <algorithm>
    #include <unordered_map>
    #include <vector>
    #include <cstring>
    #include <iostream>

    #include <bobcat/ptriter>

    using namespace std;
    using namespace FBB;

    int main()
    {
        cout << "Enter lines, the first word will be the map's key; "
                                                "^D when done.\n";

        string key;
        string line;
        unordered_map<string, string> map;
        while (cin >> key && getline(cin, line))    // fill the map
            map[key] = line;
        cout << '\n';

                                            // initialize a support
        vector<decltype(&*map.begin())>     // vector, using ptrIter
            support(ptrIter(map.begin()), ptrIter(map.end()));

                                            // sort 'support'
        typedef unordered_map<string, string>::value_type VT;
        sort(support.begin(), support.end(),
            [&](VT const *p1, VT const *p2)
            {
                return strcasecmp(p1->first.c_str(), p2->first.c_str()) < 0;
            }
        );

        for(auto &element: support)         // display sorted by key
            cout << element->first << ' ' << element->second << '\n';
    }

## FILES

bobcat/ptriter - defines the class interface

## SEE ALSO

bobcat(7)

## BUGS

None Reported.

## BOBCAT PROJECT FILES

- https://fbb-git.gitlab.io/bobcat/: gitlab project page;

Debian Bobcat project files:

- libbobcat6: debian package containing the shared library, changelog and copyright note;
- libbobcat-dev: debian package containing the static library, headers, manual pages, and developer info;

## BOBCAT

Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.

## COPYRIGHT

This is free software, distributed under the terms of the GNU General Public License (GPL).

## AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).