Using bgl to build search tree with dfs - c++

I would like to create a search tree of a graph using dfs algorithm. I get compilation errors over and over my code is like that (the compilation error is so long that I do not paste it):
typedef adjacency_list <vecS, vecS, undirectedS> Graph;
typedef graph_traits <Graph>::edge_descriptor Edge;
typedef graph_traits <Graph>::vertex_descriptor Vertex;
typedef pair<int, int> E;
vector<E> edges;
Graph g(edges.begin(), edges.end(), n);
vector<Vertex> p(n);
Vertex s = vertex(0,g);
breadth_first_search(g, s, visitor(record_predecessors(&p[0], on_tree_edge())));
Part of error:
instantiated from here
/usr/include/boost/graph/breadth_first_search.hpp:39:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘initialize_vertex’
/usr/include/boost/graph/breadth_first_search.hpp:40:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘discover_vertex’
/usr/include/boost/graph/breadth_first_search.hpp:41:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘examine_vertex’
/usr/include/boost/graph/breadth_first_search.hpp:42:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘examine_edge’
/usr/include/boost/graph/breadth_first_search.hpp:43:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘tree_edge’
/usr/include/boost/graph/breadth_first_search.hpp:44:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘non_tree_edge’
/usr/include/boost/graph/breadth_first_search.hpp:45:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘gray_target’
/usr/include/boost/graph/breadth_first_search.hpp:46:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘black_target’
/usr/include/boost/graph/breadth_first_search.hpp:47:7: error: ‘struct boost::predecessor_recorder<long unsigned int*, boost::on_tree_edge>’ has no member named ‘finish_vertex’
make: *** [file] Error 1


breadth_first_search expects a BFSVisitor. record_predecessors returns an EventVisitor. You need to use make_bfs_visitor in order to make it work.
breadth_first_search(g, s, visitor(make_bfs_visitor(record_predecessors(&p[0], on_tree_edge()))));

Related

How to fix malfunctioning G++ Complier?

The G++ complier is not working. Yesterday I was updating MinGW and Windows PATHS to get Natbeans working but now Visual Studio Code is not Saying "Hello World", It is giving 20+ errors each run.
Any ideas on how to fix so I can run my program? I Uninstalled and Reinstalled MinGw twice but it did not work
Some of the Errors:
required from 'class std::__cxx11::basic_string<char16_t>'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:5677:41:
required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:61:53:
error: no type named 'size_type' in 'struct
std::allocator_traitsstd::allocator<char16_t >'
typedef typename _Base_type::size_type size_type;
^~~~~~~~~ c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:62:53:
error: no type named 'difference_type' in 'struct
std::allocator_traitsstd::allocator<char16_t >'
typedef typename _Base_type::difference_type difference_type;
^~~~~~~~~~~~~~~ c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:70:23:
error: no members matching
'__gnu_cxx::__alloc_traitsstd::allocator<char16_t >::_Base_type {aka
std::allocator_traitsstd::allocator<char16_t >}::max_size' in
'__gnu_cxx::__alloc_traitsstd::allocator<char16_t >::_Base_type {aka
struct std::allocator_traitsstd::allocator<char16_t >}'
using _Base_type::max_size;
^~~~~~~~ In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\string:52:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\locale_classes.h:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\ios_base.h:41,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:42,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
from test17.cpp:23: c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h: In
member function 'size_t std::hashstd::__cxx11::basic_string<char16_t
::operator()(const u16string&) const': c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:5678:42:
error: 'const u16string {aka const class
std::__cxx11::basic_string<char16_t>}' has no member named 'length'
__s.length() * sizeof(char16_t)); }
^~~~~~ In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:40:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\string:52,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\locale_classes.h:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\ios_base.h:41,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:42,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
from test17.cpp:23: c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h: In
instantiation of 'struct
__gnu_cxx::__alloc_traitsstd::allocator<char32_t >': c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:75:24:
required from 'class std::__cxx11::basic_string<char32_t>'
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:5692:41:
required from here
c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:61:53:
error: no type named 'size_type' in 'struct
std::allocator_traitsstd::allocator<char32_t >'
typedef typename _Base_type::size_type size_type;
^~~~~~~~~ c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:62:53:
error: no type named 'difference_type' in 'struct
std::allocator_traitsstd::allocator<char32_t >'
typedef typename _Base_type::difference_type difference_type;
^~~~~~~~~~~~~~~ c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ext\alloc_traits.h:70:23:
error: no members matching
'__gnu_cxx::__alloc_traitsstd::allocator<char32_t >::_Base_type {aka
std::allocator_traitsstd::allocator<char32_t >}::max_size' in
'__gnu_cxx::__alloc_traitsstd::allocator<char32_t >::_Base_type {aka
struct std::allocator_traitsstd::allocator<char32_t >}'
using _Base_type::max_size;
^~~~~~~~ In file included from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\string:52:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\locale_classes.h:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\ios_base.h:41,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:42,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
from test17.cpp:23: c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h: In
member function 'size_t std::hashstd::__cxx11::basic_string<char32_t
::operator()(const u32string&) const': c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\basic_string.h:5693:42:
error: 'const u32string {aka const class
std::__cxx11::basic_string<char32_t>}' has no member named 'length'
The Code so far (Want it to print Hello World to the Console using C++):
#include <iostream>
int main()
{
//Prints Hello World to the Console
std::cout << "Hello World" << std::endl;
}
Desired output:
"Hello World"

c++11 unordered_set with hash function syntax error

I've this code:
#include<unordered_set>
using namespace std;
struct E{
size_t distance;
bool operator>(const E& e)const{
return distance > e.distance;
}
bool operator<(const E& e)const{
return distance < e.distance;
}
};
int main(){
unordered_set<E> s;
return 0;
}
When I compile it with g++ 7.3 it gives a lot of errors:
g++ m.cpp -std=c++11
In file included from /usr/include/c++/7/bits/hashtable.h:35:0,
from /usr/include/c++/7/unordered_set:47,
from m.cpp:1:
/usr/include/c++/7/bits/hashtable_policy.h: In instantiation of ‘struct std::__detail::__is_noexcept_hash<E, std::hash<E> >’:
/usr/include/c++/7/type_traits:143:12: required from ‘struct std::__and_<std::__is_fast_hash<std::hash<E> >, std::__detail::__is_noexcept_hash<E, std::hash<E> > >’
/usr/include/c++/7/type_traits:154:31: required from ‘struct std::__not_<std::__and_<std::__is_fast_hash<std::hash<E> >, std::__detail::__is_noexcept_hash<E, std::hash<E> > > >’
/usr/include/c++/7/bits/unordered_set.h:98:63: required from ‘class std::unordered_set<E>’
m.cpp:13:22: required from here
/usr/include/c++/7/bits/hashtable_policy.h:87:34: error: no match for call to ‘(const std::hash<E>) (const E&)’
noexcept(declval<const _Hash&>()(declval<const _Key&>()))>
~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/7/bits/move.h:54:0,
from /usr/include/c++/7/bits/stl_pair.h:59,
from /usr/include/c++/7/utility:70,
from /usr/include/c++/7/unordered_set:38,
from m.cpp:1:
/usr/include/c++/7/type_traits: In instantiation of ‘struct std::__not_<std::__and_<std::__is_fast_hash<std::hash<E> >, std::__detail::__is_noexcept_hash<E, std::hash<E> > > >’:
/usr/include/c++/7/bits/unordered_set.h:98:63: required from ‘class std::unordered_set<E>’
m.cpp:13:22: required from here
/usr/include/c++/7/type_traits:154:31: error: ‘value’ is not a member of ‘std::__and_<std::__is_fast_hash<std::hash<E> >, std::__detail::__is_noexcept_hash<E, std::hash<E> > >’
: public __bool_constant<!bool(_Pp::value)>
Where did I get wrong, how to fix it?

std::unordered_set does not require operator< and operator> for your type E, which you have provided. It does require a hash function or function-like object (or defaults to std::hash<E>) which you have not provided, as well as operator==, which you have also not provided.

If you cannot provide std::hash<E> you can switch to a std::map which will be slower though.

How to use unordered_map in base class with curiously recurring template pattern?

I'm using curiously recurring template pattern:
#include <unordered_map>
using namespace std;
template<class S>
struct State {
unordered_map<int, S> children; // <-- problem!
};
struct TicTacToeState : public State<TicTacToeState> {
// implementation
};
int main() {
return 0;
}
Basically, I want to have an unordered_map of children states in a (base) State.
Compile with g++ file.cpp -std=c++11:
In file included from /usr/include/c++/4.8/utility:70:0,
from /usr/include/boost/config/no_tr1/utility.hpp:21,
from /usr/include/boost/config/select_stdlib_config.hpp:37,
from /usr/include/boost/config.hpp:40,
from /usr/include/boost/functional/hash/hash_fwd.hpp:17,
from /usr/include/boost/functional/hash/hash.hpp:13,
from /usr/include/boost/functional/hash.hpp:6,
from tests/../examples/tic_tac_toe.cpp:1,
from tests/test_tic_tac_toe.cpp:3:
/usr/include/c++/4.8/bits/stl_pair.h: In instantiation of ‘struct std::pair<const long unsigned int, TicTacToeState>’:
/usr/include/c++/4.8/type_traits:615:28: required from ‘struct std::__is_destructible_impl<std::pair<const long unsigned int, TicTacToeState> >’
/usr/include/c++/4.8/type_traits:637:12: required from ‘struct std::__is_destructible_safe<std::pair<const long unsigned int, TicTacToeState>, false, false>’
/usr/include/c++/4.8/type_traits:652:12: required from ‘struct std::is_destructible<std::pair<const long unsigned int, TicTacToeState> >’
/usr/include/c++/4.8/type_traits:116:12: required from ‘struct std::__and_<std::is_destructible<std::pair<const long unsigned int, TicTacToeState> >, std::__is_direct_constructible_impl<std::pair<const long unsigned int, TicTacToeState>, const std::pair<const long unsigned int, TicTacToeState>&> >’
/usr/include/c++/4.8/type_traits:817:12: required from ‘struct std::__is_direct_constructible_new_safe<std::pair<const long unsigned int, TicTacToeState>, const std::pair<const long unsigned int, TicTacToeState>&>’
/usr/include/c++/4.8/type_traits:895:12: [ skipping 5 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/usr/include/c++/4.8/type_traits:974:12: required from ‘struct std::is_copy_constructible<std::pair<const long unsigned int, TicTacToeState> >’
/usr/include/c++/4.8/bits/alloc_traits.h:540:12: required from ‘struct std::__is_copy_insertable<std::allocator<std::pair<const long unsigned int, TicTacToeState> > >’
/usr/include/c++/4.8/bits/alloc_traits.h:560:63: required by substitution of ‘template<class _Alloc> using __check_copy_constructible = std::__allow_copy_cons<std::__is_copy_insertable<_Alloc>::value> [with _Alloc = std::allocator<std::pair<const long unsigned int, TicTacToeState> >]’
/usr/include/c++/4.8/bits/unordered_map.h:97:11: required from ‘class std::unordered_map<long unsigned int, TicTacToeState, std::hash<long unsigned int>, std::equal_to<long unsigned int>, std::allocator<std::pair<const long unsigned int, TicTacToeState> > >’
tests/../examples/../gtsa.hpp:110:30: required from ‘struct State<TicTacToeState, TicTacToeMove>’
tests/../examples/tic_tac_toe.cpp:69:32: required from here
/usr/include/c++/4.8/bits/stl_pair.h:102:11: error: ‘std::pair<_T1, _T2>::second’ has incomplete type
_T2 second; /// #c second is a copy of the second object
^
In file included from tests/test_tic_tac_toe.cpp:3:0:
tests/../examples/tic_tac_toe.cpp:69:8: error: forward declaration of ‘struct TicTacToeState’
struct TicTacToeState : public State<TicTacToeState, TicTacToeMove> {
^
In file included from /usr/include/c++/4.8/utility:70:0,
from /usr/include/boost/config/no_tr1/utility.hpp:21,
from /usr/include/boost/config/select_stdlib_config.hpp:37,
from /usr/include/boost/config.hpp:40,
from /usr/include/boost/functional/hash/hash_fwd.hpp:17,
from /usr/include/boost/functional/hash/hash.hpp:13,
from /usr/include/boost/functional/hash.hpp:6,
from tests/../examples/tic_tac_toe.cpp:1,
from tests/test_tic_tac_toe.cpp:3:
/usr/include/c++/4.8/bits/stl_pair.h: In instantiation of ‘constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&) [with _U1 = long unsigned int&; _U2 = TicTacToeState&; <template-parameter-2-3> = void; _T1 = const long unsigned int; _T2 = TicTacToeState]’:
tests/../examples/../gtsa.hpp:640:57: required from ‘S* MonteCarloTreeSearch<S, M>::add_child(S*, M&) [with S = TicTacToeState; M = TicTacToeMove]’
tests/../examples/../gtsa.hpp:472:41: required from ‘S* MonteCarloTreeSearch<S, M>::tree_policy(S*, S*) [with S = TicTacToeState; M = TicTacToeMove]’
tests/../examples/../gtsa.hpp:453:44: required from ‘void MonteCarloTreeSearch<S, M>::monte_carlo_tree_search(S*) [with S = TicTacToeState; M = TicTacToeMove]’
tests/../examples/../gtsa.hpp:433:41: required from ‘M MonteCarloTreeSearch<S, M>::get_move(S*) [with S = TicTacToeState; M = TicTacToeMove]’
tests/test_tic_tac_toe.cpp:123:1: required from here
/usr/include/c++/4.8/bits/stl_pair.h:145:64: error: using invalid field ‘std::pair<_T1, _T2>::second’
: first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
^
My understanding is:
I'm asking to create a struct TicTacToeState, it looks what's the base class, aha, it's template, fine, it tries to instantiate State with S = TicTacToeState but fails, because unordered_map<int, S> needs already defined type for map values, but TicTacToeState wasn't defined.
Placing TicTacToeState in front won't help, because then it will have no State declaration at hand.
If somebody would like to have a broader look at the original code, State is defined here. I use CRTP for the first time, maybe I don't need it and it's only complicating the code? I don't know, I haven't found anything simpler.
How to make it work?

Classes/structs can't have members which are incomplete types, so they cannot refer to itself, since they need a definition of itself to form this class.
Since looping over std::unordered_map should give you a reference to std::pair<const Key, Value> it requires a complete type.
So, in order to do something like this, you'll have to use a wrapper class which makes use of allocations, allowing you to first complete the type and use it elsewhere.
In most cases I would use std::unordered_map<int, std::unique_ptr<S>>, though if you really require the element to be created, you can wrap it.
struct SWrapper final
{
SWrapper();
operator S&() { return *_S; }
operator const S&() const { return *_S; }
private:
std::unique_ptr<S> _S;
};
// In .cpp
SWrapper::SWrapper() : _S(std::make_unique<S>()) {}

Errors building STLPort

I'm trying to use STLPort in my project, and when I follow the directions in INSTALL.unixes I get compile errors.
I ran ./configure, then make, the output is below. I'm using make 3.81 and gcc 4.6.1 on Ubuntu.
Edit: I tried adding --with-extra-cxxflags="-std=c++ox" and I get a different and smaller set of errors, listed below.
In file included from ../stlport/memory:45:0,
from reachable.cc:16:
../stlport/stl/_shared_ptr.h:377:43: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:421:39: error: declaration of ‘operator=’ as non-function
../stlport/stl/_shared_ptr.h:421:26: error: expected ‘;’ at end of member declaration
../stlport/stl/_shared_ptr.h:421:39: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:463:17: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:536:43: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:552:39: error: declaration of ‘operator=’ as non-function
../stlport/stl/_shared_ptr.h:552:26: error: expected ‘;’ at end of member declaration
../stlport/stl/_shared_ptr.h:552:39: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:591:17: error: ‘nullptr_t’ has not been declared
In file included from ../stlport/memory:45:0,
from reachable.cc:16:
../stlport/stl/_shared_ptr.h:643:45: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:647:18: error: declaration of ‘operator==’ as non-function
../stlport/stl/_shared_ptr.h:647:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:647:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:647:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:647:50: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:647:53: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:651:45: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:655:18: error: declaration of ‘operator!=’ as non-function
../stlport/stl/_shared_ptr.h:655:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:655:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:655:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:655:50: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:655:53: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:660:44: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:665:17: error: declaration of ‘operator<’ as non-function
../stlport/stl/_shared_ptr.h:665:17: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:665:17: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:665:28: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:665:49: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:665:52: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:669:44: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:673:17: error: declaration of ‘operator>’ as non-function
../stlport/stl/_shared_ptr.h:673:17: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:673:17: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:673:28: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:673:49: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:673:52: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:677:45: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:681:18: error: declaration of ‘operator<=’ as non-function
../stlport/stl/_shared_ptr.h:681:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:681:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:681:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:681:50: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:681:53: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:685:45: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:689:18: error: declaration of ‘operator>=’ as non-function
../stlport/stl/_shared_ptr.h:689:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:689:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:689:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:689:50: error: expected primary-expression before ‘>’ token
../stlport/stl/_shared_ptr.h:689:53: error: ‘x’ was not declared in this scope
../stlport/stl/_shared_ptr.h:775:26: error: expected ‘)’ before ‘,’ token
../stlport/stl/_shared_ptr.h:790:26: error: expected ‘)’ before ‘,’ token
../stlport/stl/_shared_ptr.h:917:43: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:1160:26: error: expected ‘)’ before ‘,’ token
../stlport/stl/_shared_ptr.h:1175:26: error: expected ‘)’ before ‘,’ token
../stlport/stl/_shared_ptr.h:1296:43: error: function definition does not declare parameters
../stlport/stl/_shared_ptr.h:1553:42: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1557:18: error: declaration of ‘operator==’ as non-function
../stlport/stl/_shared_ptr.h:1557:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1557:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1557:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:1561:42: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1565:18: error: declaration of ‘operator!=’ as non-function
../stlport/stl/_shared_ptr.h:1565:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1565:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1565:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:1569:41: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1573:17: error: declaration of ‘operator<’ as non-function
../stlport/stl/_shared_ptr.h:1573:17: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1573:17: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1573:28: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:1577:42: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1581:18: error: declaration of ‘operator<=’ as non-function
../stlport/stl/_shared_ptr.h:1581:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1581:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1581:29: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:1585:41: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1589:17: error: declaration of ‘operator>’ as non-function
../stlport/stl/_shared_ptr.h:1589:17: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1589:17: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1589:28: error: expected primary-expression before ‘const’
../stlport/stl/_shared_ptr.h:1593:42: error: ‘nullptr_t’ has not been declared
../stlport/stl/_shared_ptr.h:1597:18: error: declaration of ‘operator>=’ as non-function
../stlport/stl/_shared_ptr.h:1597:18: error: ‘nullptr_t’ was not declared in this scope
../stlport/stl/_shared_ptr.h:1597:18: note: suggested alternative:
/usr/include/c++/4.6/i686-linux-gnu/./bits/c++config.h:159:29: note: ‘std::nullptr_t’
../stlport/stl/_shared_ptr.h:1597:29: error: expected primary-expression before ‘const’
In file included from ../stlport/stl/_hashtable.h:541:0,
from ../stlport/stl/_unordered_map.h:24,
from ../stlport/unordered_map:28,
from reachable.cc:17:
../stlport/stl/_hashtable.c: In member function ‘stlp_std::pair<stlp_std::priv::_Ht_iterator<typename stlp_std::forward_list<_Val, _All>::iterator, typename _Traits::_NonConstTraits>, bool> stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::insert_unique_noresize(const value_type&) [with _Val = stlp_std::pair<void* const, long unsigned int>, _Key = void*, _HF = stlp_std::hash<void*>, _Traits = stlp_std::priv::_UnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> >, _ExK = stlp_std::priv::_Select1st<stlp_std::pair<void* const, long unsigned int> >, _EqK = stlp_std::equal_to<void*>, _All = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >, typename _Traits::_NonConstTraits = stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> >, typename stlp_std::forward_list<_Val, _All>::iterator = stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::value_type = stlp_std::pair<void* const, long unsigned int>]’:
../stlport/stl/_hashtable.c:251:41: instantiated from ‘stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::_M_insert(const value_type&) [with _Val = stlp_std::pair<void* const, long unsigned int>, _Key = void*, _HF = stlp_std::hash<void*>, _Traits = stlp_std::priv::_UnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> >, _ExK = stlp_std::priv::_Select1st<stlp_std::pair<void* const, long unsigned int> >, _EqK = stlp_std::equal_to<void*>, _All = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference = stlp_std::pair<void* const, long unsigned int>&, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::value_type = stlp_std::pair<void* const, long unsigned int>]’
../stlport/stl/_unordered_map.h:130:22: instantiated from ‘_Tp& stlp_std::unordered_map<_Key, _Tp, _HashFcn, _EqualKey, _Alloc>::operator[](const _KT&) [with _KT = void*, _Key = void*, _Tp = long unsigned int, _HashFcn = stlp_std::hash<void*>, _EqualKey = stlp_std::equal_to<void*>, _Alloc = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >]’
reachable.cc:45:27: instantiated from here
../stlport/stl/_hashtable.c:206:59: error: use of deleted function ‘stlp_std::pair<_T1, _T2>::pair(stlp_std::pair<_T1, _T2>&&) [with _T1 = stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, _T2 = bool, stlp_std::pair<_T1, _T2> = stlp_std::pair<stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, bool>]’
In file included from ../stlport/stl/_alloc.h:53:0,
from ../stlport/memory:30,
from reachable.cc:16:
../stlport/utility:140:3: error: ‘stlp_std::pair<_T1, _T2>::pair(stlp_std::pair<_T1, _T2>&&) [with _T1 = stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, _T2 = bool, stlp_std::pair<_T1, _T2> = stlp_std::pair<stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, bool>]’ is implicitly deleted because the default definition would be ill-formed:
../stlport/utility:140:3: error: non-static data member ‘stlp_std::pair<stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, bool>::first’ does not have a move constructor or trivial copy constructor
In file included from ../stlport/stl/_hashtable.h:541:0,
from ../stlport/stl/_unordered_map.h:24,
from ../stlport/unordered_map:28,
from reachable.cc:17:
../stlport/stl/_hashtable.c:251:41: instantiated from ‘stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::_M_insert(const value_type&) [with _Val = stlp_std::pair<void* const, long unsigned int>, _Key = void*, _HF = stlp_std::hash<void*>, _Traits = stlp_std::priv::_UnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> >, _ExK = stlp_std::priv::_Select1st<stlp_std::pair<void* const, long unsigned int> >, _EqK = stlp_std::equal_to<void*>, _All = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference = stlp_std::pair<void* const, long unsigned int>&, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::value_type = stlp_std::pair<void* const, long unsigned int>]’
../stlport/stl/_unordered_map.h:130:22: instantiated from ‘_Tp& stlp_std::unordered_map<_Key, _Tp, _HashFcn, _EqualKey, _Alloc>::operator[](const _KT&) [with _KT = void*, _Key = void*, _Tp = long unsigned int, _HashFcn = stlp_std::hash<void*>, _EqualKey = stlp_std::equal_to<void*>, _Alloc = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >]’
reachable.cc:45:27: instantiated from here
../stlport/stl/_hashtable.c:216:54: error: use of deleted function ‘stlp_std::pair<_T1, _T2>::pair(stlp_std::pair<_T1, _T2>&&) [with _T1 = stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, _T2 = bool, stlp_std::pair<_T1, _T2> = stlp_std::pair<stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, bool>]’
../stlport/stl/_hashtable.c:251:41: instantiated from ‘stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::_M_insert(const value_type&) [with _Val = stlp_std::pair<void* const, long unsigned int>, _Key = void*, _HF = stlp_std::hash<void*>, _Traits = stlp_std::priv::_UnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> >, _ExK = stlp_std::priv::_Select1st<stlp_std::pair<void* const, long unsigned int> >, _EqK = stlp_std::equal_to<void*>, _All = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::reference = stlp_std::pair<void* const, long unsigned int>&, stlp_std::hashtable<_Val, _Key, _HF, _Traits, _ExK, _EqK, _All>::value_type = stlp_std::pair<void* const, long unsigned int>]’
../stlport/stl/_unordered_map.h:130:22: instantiated from ‘_Tp& stlp_std::unordered_map<_Key, _Tp, _HashFcn, _EqualKey, _Alloc>::operator[](const _KT&) [with _KT = void*, _Key = void*, _Tp = long unsigned int, _HashFcn = stlp_std::hash<void*>, _EqualKey = stlp_std::equal_to<void*>, _Alloc = stlp_std::allocator<stlp_std::pair<void* const, long unsigned int> >]’
reachable.cc:45:27: instantiated from here
../stlport/stl/_hashtable.c:219:67: error: use of deleted function ‘stlp_std::pair<_T1, _T2>::pair(stlp_std::pair<_T1, _T2>&&) [with _T1 = stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, _T2 = bool, stlp_std::pair<_T1, _T2> = stlp_std::pair<stlp_std::priv::_Ht_iterator<stlp_std::priv::_Slist_iterator<stlp_std::pair<void* const, long unsigned int>, stlp_std::_Nonconst_traits<stlp_std::pair<void* const, long unsigned int> > >, stlp_std::priv::_NonLocalUnorderedMapTraitsT<stlp_std::pair<void* const, long unsigned int> > >, bool>]’
make[1]: *** [obj/gcc/so/reachable.o] Error 1
make: *** [release-shared] Error 2

It turns out the source I got my copy of STLPort from, git://stlport.git.sourceforge.net/gitroot/stlport/stlport, is much more bleeding edge than I thought. If I grab the stable build from SourceForge it compiles fine.

Why does iostream include time.h?

Consider this code:
#include <iostream>
template<class C>
struct time { };
int main() { }
It produces (GCC 4.5):
error: ‘template<class C> struct time’ redeclared as different kind of symbol
/usr/include/time.h:186:15: error: previous declaration of ‘time_t time(time_t*)’
Why does iostream include time_t time(time_t*) ?
Why does iostream include time_t time(time_t*) outside std namespace?
(unanswered) Why, if I remove template<class C>, do I not get this error?

If you run g++ -H -Wall -c testim.cc (where testim.cc is your example) you'll see that
.... /usr/include/c++/4.6/bits/ios_base.h
..... /usr/include/c++/4.6/ext/atomicity.h
...... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr.h
....... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr-default.h
........ /usr/include/pthread.h
......... /usr/include/sched.h
.......... /usr/lib/gcc/x86_64-linux-gnu/4.6/include/stddef.h
.......... /usr/include/time.h
So <time.h> is included for pthread support.
This is with GCC 4.6 on Debian/Sid/AMD64

Seems to be for locale support on my box:
$ cat whytime.cc
#define _TIME_H_
#include <iostream>
int main() {
std::cout << "hello, world" << std::endl;
return 0;
}
$ g++ -Wall -Werror -Wextra -ansi -o whytime whytime.cc && ./whytime
In file included from /usr/include/c++/4.2.1/cwchar:52,
from /usr/include/c++/4.2.1/bits/postypes.h:46,
from /usr/include/c++/4.2.1/iosfwd:49,
from /usr/include/c++/4.2.1/ios:43,
from /usr/include/c++/4.2.1/ostream:45,
from /usr/include/c++/4.2.1/iostream:45,
from whytime.cc:2:
/usr/include/c++/4.2.1/ctime:66: error: ‘::clock_t’ has not been declared
/usr/include/c++/4.2.1/ctime:68: error: ‘::tm’ has not been declared
/usr/include/c++/4.2.1/ctime:70: error: ‘::clock’ has not been declared
/usr/include/c++/4.2.1/ctime:71: error: ‘::difftime’ has not been declared
/usr/include/c++/4.2.1/ctime:72: error: ‘::mktime’ has not been declared
/usr/include/c++/4.2.1/ctime:73: error: ‘::time’ has not been declared
/usr/include/c++/4.2.1/ctime:74: error: ‘::asctime’ has not been declared
/usr/include/c++/4.2.1/ctime:75: error: ‘::ctime’ has not been declared
/usr/include/c++/4.2.1/ctime:76: error: ‘::gmtime’ has not been declared
/usr/include/c++/4.2.1/ctime:77: error: ‘::localtime’ has not been declared
/usr/include/c++/4.2.1/ctime:78: error: ‘::strftime’ has not been declared
In file included from /usr/include/c++/4.2.1/locale:46,
from /usr/include/c++/4.2.1/bits/ostream.tcc:46,
from /usr/include/c++/4.2.1/ostream:572,
from /usr/include/c++/4.2.1/iostream:45,
from whytime.cc:2:
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘_InIter std::time_get<_CharT, _InIter>::_M_extract_via_format(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*, const _CharT*) const’:
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1839: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1846: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1854: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1861: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1873: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1880: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1883: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1895: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1900: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1908: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1912: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1932: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1968: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1976: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_weekday(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’:
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2210: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_monthname(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’:
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2259: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_year(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’:
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2288: error: invalid use of incomplete type ‘struct tm’
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’

Apparently GCC's iostream needs something in time for something.
time_t is a C language thing, which doesn't have namespaces, and so for backwards comparability-ish, it is in both the std namespace, and not in the std namespace.
As for why there's no errors, I'm not 100% sure. I know C could have functions and structs with the same name, and structs were qualified with the name struct so that the compiler could tell them apart. C++ compilers thinks it's a function, unless preceeded with the struct keyword. http://ideone.com/XZB2M v http://ideone.com/kWMKE. I guess it also allows that for backwards comparability?