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Using Overloaded Operator [] via Access Function

I have an accessor function that returns a const reference to a type (std :: map) ......

myMap_t const& getMap() const {return paramMap;}

The type has an overloaded operator []. What is the syntax to then use the statement []directly from the getter function in the manner described below, but it really works.

parameter = contextObj.getMap()[key];

Error message:

context.cpp:35: error: passing   
  'const std::map<
     std::basic_string<char, std::char_traits<char>, std::allocator<char> >, 
     float, 
     std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, 
     std::allocator<std::pair<
       const std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
       float> > >'
as 'this' argument of 
  '_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&)  
with 
  _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
  _Tp = float, 
  _Compare = std::less<std::basic_string<char, std::char_traits<char>,  td::allocator<char> > >, 
  _Alloc = std::allocator<std::pair<
    const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, 
    float> >]' 
discards qualifiers
+3
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4 answers

, operator[] , const . , , , , , , , , .

const, , ( ), std::map<>::find, . , m.end()

+6

std::map const, std::map::operator[] const, .
, : (A) .find []

auto iter = contextObj.getMap().find( key );
if (iter != contextObj.getMap().end())
    param = iter->second;

(B) const ( )
(C) ( )

+3

const myMap_t& getMap(). myMap_t typedef std::map. operator[] of std::map ( const), ( , ). , :

  • contextObj.getMap().find(key) contextObj.getMap()[key], ( map.end(), )
  • return myMap_t& ( const), , operator[]
+1
context.cpp:35: error: passing   
  'const std::map<
     std::basic_string<char, std::char_traits<char>, std::allocator<char> >, 
     float, 
     std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, 
     std::allocator<std::pair<
       const std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
       float> > >'
as 'this' argument of 
  '_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&)  
with 
  _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
  _Tp = float, 
  _Compare = std::less<std::basic_string<char, std::char_traits<char>,  td::allocator<char> > >, 
  _Alloc = std::allocator<std::pair<
    const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, 
    float> >' 
discards qualifiers

std::basic_string - , std::string, std::string - , char. , :

context.cpp:35: error: passing   
  'const std::map<
     std::string, 
     float, 
     std::less<std::string>, 
     std::allocator<std::pair<const std::string, float> >
  >'
as 'this' argument of 
  '_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&)  
with 
  _Key = std::string,
  _Tp = float, 
  _Compare = std::less<std::string>, 
  _Alloc = std::allocator<std::pair<const std::string> >' 
discards qualifiers

_Compare () _Alloc (allocator) , ; , _Key _Tp :

context.cpp:35: error: passing   
  'const std::map<std::string, float>'
as 'this' argument of 
  'float& std::map<std::string, float>::operator[](const std::string&)  
discards qualifiers

, . operator[] std::map<std::string, float>, const std::map<std::string, float> (.. this ). " ", , const.

, operator[] const, .. . , , .

? :

x , .

x , . , , ( ).

( ).

, , .

Why is he doing this? Well, we already have a question for this .

+1
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