comparing and deleting derived classes

[luki]

Hi,

I am creating a program that stores cities with their geographical points so that I can measure the distance between them. these cities will be stored in derived classes using vectors. ATM I'm having a hard time to try and code ways to prevent a city from being entered twice, I imagine you would use a find() function ? and also how can I delete a city (a specific derived class) ?

the base class will be structured something like this:

class city
{
double latitude, longitude;
char name[255];

};

revealing my whole program will be too much to read and I'm only expecting some sort of guidance. I'm quite new with vectors.

[firedraco]

Mmmm, well if you are using the default comparison operator (you might want to define it just in case), then you can use an std::set instead of an std::vector. Read:

http://www.cplusplus.com/reference/stl/set/

[Bazzy]

Why do you need derived classes?

the function 'count' should be better that 'find' to check if a value was already entered.
In order to use it, you should provide a == operator for 'city'
eg:

bool operator == (const city &a, const city &b)
{
        return !strcmp(a.name,b.name) && a.latitude==b.latitude && a.longitude==b.longitude;
}

http://www.cplusplus.com/reference/algorithm/count/

[luki]

Hi bazzy,

I tried implementing the example code above that you showed but I get these errors...


in function int main()':
line 1 : expected `,' or `..' before '&' token
line 3 : a function-definition is not allowed here before '{' token
line 3 : expected `,' before '{' token
[Build Error] [main.o] Error 1

what's wrong ??

[jsmith]

Couple of things:

1) name should really be a std::string instead of a char array;
2) you can't compare doubles for equality;
3) the default operator== should then suffice;
4) both count() and find() are O(n) so neither is really any better than the other.

And why do you need derived classes?

[luki]

you guys are right, there is no need of derived class since each city will have the same member variables.