I have a simple template class:
namespace test
{
template< class Key, class Value, class Container = std::map< Key, Value > >
class DB
{
public:
static DB& instance()
{
static DB _instance;
return _instance;
}
private:
DB(){};
DB( DB const& ){};
void operator=( DB const& ){};
Container _db_internal;
};
}
When I debug in gdb I want to see the _db_internal container, but don't know how to access it.
I tried writing in gdb:
p 'test::DB<std::string, someclass*, std::tr1::unordered_map< std::string, someclass* > >::instance()::_instance'._db_internal
and it gives me: No symbol ... in current context
also tried without single quotes but no luck.
How to print that container in gdb? I'm using gdb version: 7.6.1
Thanks
As suggested using gdb autocomplete I was able to get this:
p 'test::DB<std::string, std::string, std::map<std::string, std::string, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > > >::instance()::_instance'
but that gives me 0 which is not good
then if I tried:
p 'test::DB<std::string, std::string, std::map<std::string, std::string, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > > >::instance()::_instance._db_internal'
I also got an error saying:
No symbol "test::DB<std::string, std::string, std::map<std::string, std::string, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > > >::instance()::_instance._db_internal" in current context.
but that gives me 0 which is not good
That seems to be a bug in GDB, still present in GDB built from git as of a few days ago. This works:
(gdb) start
Temporary breakpoint 1 at 0x400865: file foo.cc, line 27.
Starting program: /tmp/a.out
Temporary breakpoint 1, main () at foo.cc:27
27 auto& db = test::DB<int, int>::instance();
(gdb) n
28 return 0;
(gdb) p 'test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance'
$1 = 0
That reproduced your behavior. Let's find out where the _instance
resides:
(gdb) info var _instance
All variables matching regular expression "_instance":
Non-debugging symbols:
0x0000000000602088 guard variable for test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance
0x00000000006020a0 test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance
... and interpret the address 0x00000000006020a0
as a pointer to desired type:
(gdb) p ('test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >' *)0x00000000006020a0
$2 = (test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > > *) 0x6020a0 <test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance>
Finally we can dereference it:
(gdb) p *$
$3 = {_db_internal = {_M_t = {_M_impl = {<std::allocator<std::_Rb_tree_node<std::pair<int const, int> > >> = {<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<int const, int> > >> = {<No data fields>}, <No data fields>},
_M_key_compare = {<std::binary_function<int, int, bool>> = {<No data fields>}, <No data fields>}, _M_header = {_M_color = std::_S_red, _M_parent = 0x0,
_M_left = 0x6020a8 <test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance+8>,
_M_right = 0x6020a8 <test::DB<int, int, std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > > >::instance()::_instance+8>}, _M_node_count = 0}}}}
P.S. I used <int,int>
as the instance, since I had to complete your snippet to a program I can compile and run. (You should have provided a complete program, but didn't).
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