How to insert a const std::shared_ptr into a std::map - c++

Question

Consider the following code:
#include <string>
#include <map>
#include <memory>
#include <utility>
#include <iostream>
typedef std::shared_ptr<const std::string> ConstDataTypePtr;
typedef std::map<std::string, ConstDataTypePtr> StrDataTypeMap;
int main()
{
StrDataTypeMap m_nameToType;
ConstDataTypePtr vp_int8(new std::string("RGH"));
m_nameToType.insert(std::make_pair<std::string, ConstDataTypePtr>("int8_t", vp_int8));
return 0;
}
You must compile it with: g++ -std=c++11 <filename>.cpp.
It gives the following error:
testO.cpp: In function ‘int main()’:
testO.cpp:14:88: error: no matching function for call to ‘make_pair(const char [7], ConstDataTypePtr&)’
m_nameToType.insert(std::make_pair<std::string, ConstDataTypePtr>("int8_t", vp_int8));
^
testO.cpp:14:88: note: candidate is:
In file included from /usr/include/c++/4.8.2/bits/stl_algobase.h:64:0,
from /usr/include/c++/4.8.2/bits/char_traits.h:39,
from /usr/include/c++/4.8.2/string:40,
from testO.cpp:1:
/usr/include/c++/4.8.2/bits/stl_pair.h:276:5: note: template<class _T1, class _T2> constexpr std::pair<typename std::__decay_and_strip<_Tp>::__type, typename std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&)
make_pair(_T1&& __x, _T2&& __y)
^
/usr/include/c++/4.8.2/bits/stl_pair.h:276:5: note: template argument deduction/substitution failed:
testO.cpp:14:88: note: cannot convert ‘vp_int8’ (type ‘ConstDataTypePtr {aka std::shared_ptr<const std::basic_string<char> >}’) to type ‘std::shared_ptr<const std::basic_string<char> >&&’
m_nameToType.insert(std::make_pair<std::string, ConstDataTypePtr>("int8_t", vp_int8));
From what I am reading of the error, the compiler is expecting an r-value when I am trying to insert into the map. Why? What mistake have I made here?
Kindly note that I created this snippet from some existing code which is part of a large code-base. It is probably also worth mentioning that the snippet has been taken from a code base which was run on Windows and I have the task of porting it to Linux. The original author had used std::tr1::shared_ptr. I modified it to use std::shared_ptr. I didn't expect any repercussions because of this change.

Answer 1

The whole point of std::make_pair is to let compiler deduce types. If you want to provide type, use std::pair<K, V>
So
m_nameToType.insert(std::make_pair<std::string, std::string>("int8_t", vp_int8));
should be:
m_nameToType.insert(std::make_pair("int8_t", vp_int8));
or
m_nameToType.insert(std::pair<const std::string, ConstDataTypePtr>("int8_t", vp_int8));
or simply:
m_nameToType.emplace("int8_t", vp_int8);

Answer 2

#include <memory>
#include <map>
#include <string>
int main() {
using shared_data = std::shared_ptr<const std::string>;
std::map<std::string, shared_data> map;
map.insert(std::make_pair(
"something",
shared_data(new std::string("something else"))
));
return 0;
}
see: http://ideone.com/4AQfqd
Back to your problem;
testO.cpp:14:83: note: cannot convert ‘vp_int8’ (type ‘ConstDataTypePtr {aka std::shared_ptr >}’) to type ‘std::basic_string&&’
m_nameToType.insert(std::make_pair("int8_t", vp_int8));
What you have:
std::make_pair<std::string, std::string>(some_string, TOTALLY_NOT_A_STRING)

Answer 3

You gave wrong types to the std::make_pair template. Just change
m_nameToType.insert(std::make_pair<std::string, std::string>("int8_t", vp_int8));
Into
m_nameToType.insert(std::make_pair<std::string, ConstDataTypePtr>(std::string("int8_t"), vp_int8));
(note the std::make_pair<std::string, ConstDataTypePtr> part)
EDIT: or don't provide template params at all, as someone suggested in comment.

Answer 4

Don't mention the types in the template in make_pair function.
m_nameToType.insert(std::make_pair("int8_t", vp_int8));