Using maps inside class and accessing values via get() and set() functions from other class

Question

I am unable to use add values this map defined in header file as protected attribute from class member function.

class xyz{
protected:
 map < string, string > *tagsMap;
public:
 xyz();
 //set Tags
 void addTag(string _tagName, string _tagValue) const;
}
// In cpp class, 
//set new Tags
void xyz::addTag(string _tagName, string _tagValue) const {
 //map < string, string > tagsMap ;
 //gives error until I uncomment above line, but thats local map
 tagsMap.insert(pair<string, string>(_tagName, _tagValue));
 // first insert function version (single parameter):
 tagsMap .insert(pair<string, string>(_tagName, _tagValue));
 for (auto& t : tagsMap )
 cout << "addTag():" << t.first << "=" << t.second << endl;
}

• andreee: Why do you need a pointer to a map?
• Sharique Javaid: i dont need a pointer.. i just want to save new values to the map on every function call and later access them...
• Joseph D.: also add ; after your class def

Answer 1

You have 3 problems:

1) Class member is declared a pointer

The commented line inside addTag():

// map < string, string > tagsMap;

It is not a pointer, which is the reason why it works if you uncomment the local map declaration.

However, this is not correct logically since it's not a member of your class - it shadows your tagsMap class member.

Thus, you need to declare tagsMap in your xyz class a non-pointer.

map < string, string > *tagsMap;
 // ^ remove asterisk '*'

2) Missing Semicolon after class definition

Add ; semicolon, after your class definition

class xyz {
 ...
}
// ^^^ add semicolon here

3) Const function

Remove const in addTag() to be able to write on tagsMap class member

void xyz::addTag(string _tagName, string _tagValue) const { .. }
 // ^^^^^ remove const
void addTag(string _tagName, string _tagValue) const;
 // ^^^^^ remove const

• Sean Burton: And if you do need to use a pointer for some reason, you need to use '->' to call member functions rather than just '.'

Answer 2

Yes pointer was not needed. It worked after making the function non-const as suggested by @codekaizer in comments above.

class xyz{
protected:
map < string, string > tagsMap;
public:
xyz();
//set Tags
void addTag(string _tagName, string _tagValue);
}

// In cpp class,

void xyz::addTag(string _tagName, string _tagValue) {
 tagsMap.insert(pair<string, string>(_tagName, _tagValue));
}