FBB::PtrIter(3bobcat) Iterator pointing to pointers FBB::PtrIter(3bobcat)

FBB::PtrIter - Iterator returning pointer when dereferenced

#include <bobcat/ptriter>

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.

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

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

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)

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.

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;

PtrIter defines the following type:

typedef decltype(&*Iterator()) PtrType:

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

#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’; }

bobcat/ptriter - defines the class interface


None Reported.

https://fbb-git.gitlab.io/bobcat/: gitlab project page;
bobcat_6.02.02-x.dsc: detached signature;
bobcat_6.02.02-x.tar.gz: source archive;
bobcat_6.02.02-x_i386.changes: change log;
libbobcat1_6.02.02-x_*.deb: debian package containing the libraries;
libbobcat1-dev_6.02.02-x_*.deb: debian package containing the libraries, headers and manual pages;

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

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

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

2005-2022 libbobcat-dev_6.02.02