Create a new structure inside a class public method - c++

Question

Hello I am trying to create a new structure inside my class but i think there is an issue with public and private scope of some sort.
typedef struct Currency
{
Currency(Coin *coin, Currency *next, int _position) : _coin(coin), _next(next), _position(0) {}
Currency() : _next(NULL), _position(0) {}
Coin *_coin;
Currency *_next;
int _position;
};
that is my structure that is inside my public section of my class
and when I try to do this
if(location <= exit)
{
start = location + 11;
begin = response.find("label", start);
end = begin - start - 3;
findStrings(start, end, s, &response);
curr._next = new Currency();
}
it says Expected type specifier for the new Currency() call.
is there something i am missing or should structures not be used this way?
class Exchange
{
public:
typedef struct Badge
{
Badge(std::string id, Badge next, Badge prev, int length) : _id(id), _next(&next), _prev(&prev), _position(length) {}
Badge() : _id(""), _next(NULL), _prev(NULL), _position(0) {}
std::string _id;
Badge *_next;
Badge *_prev;
int _position;
};
typedef struct Currency
{
Currency(Coin *coin, Currency *next, int _position) : _coin(coin), _next(next), _position(0) {}
Currency() : _next(NULL), _position(0) {}
Coin *_coin;
Currency *_next;
int _position;
};
/* constructor and destructor */
Exchange();
Exchange(std::string str);
~Exchange();
/* Assignment operator */
Exchange& operator =(const Exchange& copyExchange);
void parseTradePairs(Currency curr, const std::string response, int begin, int exit);
private:
std::string _exch;
Currency *_currencies;
Badge *_ident;
};
endif
^ that is in the class header
Exchange::Exchange()
{
_exch = "";
}
Exchange::Exchange(std::string str)
{
_exch = str;
_ident = new Badge;
_currencies = new Currency;
std::string pair;
std::string response;
CURL *curl;
getTradePairs(curl, response);
int exit = response.find_last_of("marketid");
parseTradePairs(*_currencies, response, 0, exit);
}
void parseTradePairs(Exchange::Currency curr, std::string response, int begin, int exit)
{
int start;
int end;
string s;
int location = response.find("marketid", begin);
if(location <= exit)
{
start = location + 11;
begin = response.find("label", start);
end = begin - start - 3;
findStrings(start, end, s, &response);
curr._next = new Currency();
}
}
^that is in the class cpp obviously.

Answer 1

Your function definition in the .cpp isn't related to the Exchange class. You'll need to write:
void Exchange::parseTradePairs
(Exchange::Currency curr, std::string response, int begin, int exit)
{
// ...
}
Also: Anywhere outside your class scope you'll need to use Exchange::Currency to access the type.

Answer 2

If you're instantiating Currency within a method of the class, then this should work fine.
But if you're instantiating Currency elsewhere, you'll need to scope it with the class' name.
I.e. ClassName::Currency
Of course Currency needs to be visible in the scope that you do that, and making it public should take care of that.

Answer 3

(Note: This not an answer to edited question, downvote to request deletion... :-)
One issue is this:
typedef struct Currency {
};
It compiles, but C++ compiler should say something like warning: 'typedef' was ignored in this declaration (and if it does not, enable warning!). You should use one of these:
struct Currency {
}; // type 'struct Currency' With implicit typedef in C++
which in C++ is essentially same as:
typedef struct Currency {
} Currency; // explicit typedef
or
typedef struct {
} Currency; // anonumous struct With typedef type name
It is generally best to use the first form in C++. There may be subtle differences in some corner cases, so keep things simple.
C does not do the implicit typedef, so 2nd or 3rd form are sometimes used to avoid needing to use struct keyword everywhere. This is good to know because many libraries have same .h files for both C and C++.