C++ Pointer not updating the value - c++

Question

//Inside the header.h
class telefonbok{
std::map<std::string,std::string> telebok;
std::map<std::string,std::string> aliasbok;
}
//Inside the cpp file
void telefonbok::alias(string name, string alias){
if (telebok.find(name) == telebok.end()) {
cout << "Not found" << endl;
} else {
//pointer = Adress stored in pointer.
//*pointer = Value of *pointer
string *pointer;
pointer = &telebok.find(name)->second;
aliasbok.insert(make_pair(alias, *pointer));
cout << *pointer << endl;
}
When i change the value in the first map(telebok) the second value in the map(aliasbok) stays the same (the one who is supposed to have the pointer as the value).
Example:
add peter 123
lookup peter:
peter : 123
alias peter pete
lookup pete:
pete : 123
change peter 987
lookup peter:
peter : 987
lookup pete:
pete : 123
(Pete never changes wich is the issue, it's supposed to always have the same value as peter)

Answer 1

First of all your code is inefficient (you call find twice, which is pretty expensive operation), so you should work with iterators, not pointers and it also will help to resolve your issue:
class telefonbok{
typedef std::map<std::string,std::string> Telebok;
typedef std::map<std::string,Telebok::const_iterator> Aliasbok;
Telebok telebok;
Aliasbok aliasbok;
};
void telefonbok::alias(string name, string alias)
{
Telebok::const_iterator f = telebok.find( name );
if( f == telebok.end() )
cout << "Not found" << endl;
else
aliasbok.insert( make_pair( alias, f );
}
now you have following:
you do not call std::map::find() twice
through alias you can not only find number but original name as well
to print values from alias code little bit more complicated:
for( Aliasbok::const_iterator it = aliasbok.begin(); it != aliasbok.end(); ++it )
cout << "alias " << it->first << " has number " << it->second->second << " original name " << it->second->first << endl;
or to find a value:
Aliasbok::const_iterator it = aliasbok.find( "abcd" );
if( it != aliasbok.end() )
cout << "phone for " << it->first << " is " << it->second->second << endl;
else
cout << "phone for abcd not found" << endl;
but you should get used to it when using iterators
Note: if you delete records from phonebook you need to clean aliasbook first, otherwise it will hold invalid iterators. Proper solution would be to use boost::multi_index but that probably too complicated for your level.

Answer 2

When i change the value in the first map(telebok) the second value in the map(aliasbok) stays the same (the one who is supposed to have the pointer as the value).
If the aliasbok is supposed to have pointer as the value, then your bug is that you've defined the map incorrectly. Here is your definition:
std::map<std::string,std::string> aliasbok;
Pay attention to how the value type of the map is std::string which is a value type and not std::string* which would be a pointer type.
Also pay attention to this line:
aliasbok.insert(make_pair(alias, *pointer));
Where you dereference the pointer and copy the pointed string into the pair, instead of copying a pointer.

Answer 3

You have to store shared pointers and set them apropriatelly to the same string.
class telefonbok{
std::map<std::string,std::shared_ptr<std::string>> telebok;
std::map<std::string,std::shared_ptr<std::string>> aliasbok;
}
and provide the methods to update the pointers as needed e.g.
void addphone(std::string const & name,
std::string const & alias,
std::string const & phone);
{
std::shared_ptr<std::string> phone_ptr(new std::string(phone));
telefonbok.telebok.emplace(name,phone_ptr);
telefonbok.aliasbok.emplace(alias,phone_ptr);
}
and this way when you modify the phone on either it will get updated on both. Your phone will also not die when you exit the scope of the function.
Then you can do this for updates
void update_phone(std::string const & name,
std::string const & newphone)
{
if( auto iter = telefonbok.telebok.find(name) )
{
*(iter->second.get()) = newphone;
} else if ( auto iter = telefonbok.aliasbok.find(name) )
{
*(iter->second.get()) = newphone;
}
}