On using uint32_t data type for the key and value in a map. I am getting an error no known conversion for argument.
Here is what I tried
int main() {
uint32_t a = 5;
uint32_t b = 9;
map <uint32_t, uint32_t> Mapper;
Mapper.insert({9,8});
auto imageFoundIt = Mapper.find(make_pair(a, b));
return 0;
}
Here is the error stack trace
g++ /tmp/cpzeeEDm4C.cpp
/tmp/cpzeeEDm4C.cpp: In function 'int main()':
/tmp/cpzeeEDm4C.cpp:10:52: error: no matching function for call to 'std::map<unsigned int, unsigned int>::find(std::pair<unsigned int, unsigned int>)'
10 | auto imageFoundIt = Mapper.find(make_pair(a, b));
| ^
In file included from /usr/include/c++/9/map:61,
from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:81,
from /tmp/cpzeeEDm4C.cpp:3:
/usr/include/c++/9/bits/stl_map.h:1168:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::iterator std::map<_Key, _Tp, _Compare, _Alloc>::find(const key_type&) [with _Key = unsigned int; _Tp = unsigned int; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >; std::map<_Key, _Tp, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<std::pair<const unsigned int, unsigned int> >; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = unsigned int]'
1168 | find(const key_type& __x)
| ^~~~
/usr/include/c++/9/bits/stl_map.h:1168:28: note: no known conversion for argument 1 from 'std::pair<unsigned int, unsigned int>' to 'const key_type&' {aka 'const unsigned int&'}
1168 | find(const key_type& __x)
| ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/9/bits/stl_map.h:1174:2: note: candidate: 'template<class _Kt> decltype (((std::map<_Key, _Tp, _Compare, _Alloc>*)this)->std::map<_Key, _Tp, _Compare, _Alloc>::_M_t._M_find_tr(__x)) std::map<_Key, _Tp, _Compare, _Alloc>::find(const _Kt&) [with _Kt = _Kt; _Key = unsigned int; _Tp = unsigned int; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1174 | find(const _Kt& __x) -> decltype(_M_t._M_find_tr(__x))
| ^~~~
/usr/include/c++/9/bits/stl_map.h:1174:2: note: template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_map.h: In substitution of 'template<class _Kt> decltype (((std::map<unsigned int, unsigned int>*)this)->std::map<unsigned int, unsigned int>::_M_t.std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(__x)) std::map<unsigned int, unsigned int>::find<_Kt>(const _Kt&) [with _Kt = std::pair<unsigned int, unsigned int>]':
/tmp/cpzeeEDm4C.cpp:10:52: required from here
/usr/include/c++/9/bits/stl_map.h:1174:2: error: no matching function for call to 'std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(const std::pair<unsigned int, unsigned int>&)'
In file included from /usr/include/c++/9/map:60,
from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:81,
from /tmp/cpzeeEDm4C.cpp:3:
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: candidate: 'template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) [with _Kt = _Kt; _Req = _Req; _Key = unsigned int; _Val = std::pair<const unsigned int, unsigned int>; _KeyOfValue = std::_Select1st<std::pair<const unsigned int, unsigned int> >; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1306 | _M_find_tr(const _Kt& __k)
| ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_tree.h: In substitution of 'template<class _Cmp, class _SfinaeType> using __has_is_transparent_t = typename std::__has_is_transparent<_Cmp, _SfinaeType>::type [with _Cmp = std::less<unsigned int>; _SfinaeType = std::pair<unsigned int, unsigned int>]':
/usr/include/c++/9/bits/stl_tree.h:1304:9: required by substitution of 'template<class _Kt> decltype (((std::map<unsigned int, unsigned int>*)this)->std::map<unsigned int, unsigned int>::_M_t.std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(__x)) std::map<unsigned int, unsigned int>::find<_Kt>(const _Kt&) [with _Kt = std::pair<unsigned int, unsigned int>]'
/tmp/cpzeeEDm4C.cpp:10:52: required from here
/usr/include/c++/9/bits/stl_tree.h:425:11: error: no type named 'type' in 'struct std::__has_is_transparent<std::less<unsigned int>, std::pair<unsigned int, unsigned int>, void>'
425 | using __has_is_transparent_t
| ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_map.h: In substitution of 'template<class _Kt> decltype (((std::map<unsigned int, unsigned int>*)this)->std::map<unsigned int, unsigned int>::_M_t.std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(__x)) std::map<unsigned int, unsigned int>::find<_Kt>(const _Kt&) [with _Kt = std::pair<unsigned int, unsigned int>]':
/tmp/cpzeeEDm4C.cpp:10:52: required from here
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: candidate: 'template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) const [with _Kt = _Kt; _Req = _Req; _Key = unsigned int; _Val = std::pair<const unsigned int, unsigned int>; _KeyOfValue = std::_Select1st<std::pair<const unsigned int, unsigned int> >; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1315 | _M_find_tr(const _Kt& __k) const
| ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: template argument deduction/substitution failed:
In file included from /usr/include/c++/9/map:61,
from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:81,
from /tmp/cpzeeEDm4C.cpp:3:
/usr/include/c++/9/bits/stl_map.h:1193:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator std::map<_Key, _Tp, _Compare, _Alloc>::find(const key_type&) const [with _Key = unsigned int; _Tp = unsigned int; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >; std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<const unsigned int, unsigned int> >; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = unsigned int]'
1193 | find(const key_type& __x) const
| ^~~~
/usr/include/c++/9/bits/stl_map.h:1193:28: note: no known conversion for argument 1 from 'std::pair<unsigned int, unsigned int>' to 'const key_type&' {aka 'const unsigned int&'}
1193 | find(const key_type& __x) const
| ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/9/bits/stl_map.h:1199:2: note: candidate: 'template<class _Kt> decltype (((const std::map<_Key, _Tp, _Compare, _Alloc>*)this)->std::map<_Key, _Tp, _Compare, _Alloc>::_M_t._M_find_tr(__x)) std::map<_Key, _Tp, _Compare, _Alloc>::find(const _Kt&) const [with _Kt = _Kt; _Key = unsigned int; _Tp = unsigned int; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1199 | find(const _Kt& __x) const -> decltype(_M_t._M_find_tr(__x))
| ^~~~
/usr/include/c++/9/bits/stl_map.h:1199:2: note: template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_map.h: In substitution of 'template<class _Kt> decltype (((const std::map<unsigned int, unsigned int>*)this)->std::map<unsigned int, unsigned int>::_M_t.std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(__x)) std::map<unsigned int, unsigned int>::find<_Kt>(const _Kt&) const [with _Kt = std::pair<unsigned int, unsigned int>]':
/tmp/cpzeeEDm4C.cpp:10:52: required from here
/usr/include/c++/9/bits/stl_map.h:1199:2: error: no matching function for call to 'std::_Rb_tree<unsigned int, std::pair<const unsigned int, unsigned int>, std::_Select1st<std::pair<const unsigned int, unsigned int> >, std::less<unsigned int>, std::allocator<std::pair<const unsigned int, unsigned int> > >::_M_find_tr(const std::pair<unsigned int, unsigned int>&) const'
In file included from /usr/include/c++/9/map:60,
from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:81,
from /tmp/cpzeeEDm4C.cpp:3:
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: candidate: 'template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) [with _Kt = _Kt; _Req = _Req; _Key = unsigned int; _Val = std::pair<const unsigned int, unsigned int>; _KeyOfValue = std::_Select1st<std::pair<const unsigned int, unsigned int> >; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1306 | _M_find_tr(const _Kt& __k)
| ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: candidate: 'template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) const [with _Kt = _Kt; _Req = _Req; _Key = unsigned int; _Val = std::pair<const unsigned int, unsigned int>; _KeyOfValue = std::_Select1st<std::pair<const unsigned int, unsigned int> >; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, unsigned int> >]'
1315 | _M_find_tr(const _Kt& __k) const
| ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: template argument deduction/substitution failed:
How can I use uint32_t as key and value here?
>Solution :
The problem is that std::map::find takes the key(which is of type Key) value of the element to search for as argument but you’re providing a std::pair and hence the error.
So solve this just replace the call to find with:
//------------------------------v--->pass the key value
auto imageFoundIt = Mapper.find(a)
which will give return an iterator to an element with key equivalent to key. And if no such element is found, past-the-end iterator will be returned.