FBB::PtrIter(3bobcat) | Error handler | 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 contents, 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.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
std::iterator<std::input_iterator_tag, ...>
The copy and move constructors are available.
PtrIter<set<string>::iterator> PtrIter(mySet.begin());
PtrIter defines the following type:
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.
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).
2005-2018 | libbobcat-dev_4.08.06-x.tar.gz |