c++ classes not talking [closed] - c++

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i am using gvim to do c++ for a class (since we are told we have to do it in linux, and the class is taught using c++). i have had java classes before, but this teacher isn't really telling us how to do things in c++ or linux since he states it's another class that just uses c++.
the problem i am having for my homework is that we have to create some classes and have them get info to each other, but i keep getting errors whenever i try to compile. (i can't seem to figure out how to get them to talk to each other and use functions/variables from one another.)
ex:
class a {
string user;
public: string user2;
public: vector<string> friendList;
public: void userName()
{
cout output
cin >> user;
}
public: void addFriend()
{
cout output
cin >> user2;
friendList.push_back(user2);
}
public: string getName()
{
return user;
}
};
(have tried this second class 2 ways and neither work)
way1--->
class b {
string message, username;
a User;
public: void postMessage()
{
cout ____
getline(cin, message);
username = User.getName();
}
};
or this way---->
class b: public a {
string message, username;
a User;
public: void postMessage()
{
cout ____
getline(cin, message);
username = User.getName();
}
};
(or had the function like this:)
public: void postMessage()
{
cout ____
getline(cin, message);
username = user2;
}
};
the classes don't seem to talk to each other either way, and i'm not sure how to get them to since these ways don't work and that's what was in the book/what i found on the internet so far.
so i guess my question is how can i get a to talk to b so b can use functions or variables from a? need to know so the classes can talk to eachother and also so i can get the main function to also call each class (each class is in a separate .cpp file btw).
EDIT:
(the classes are in different files)
i made a script for the terminal for the errors:
Script started on Sun 29 Sep 2013 02:27:42 PM CDT
]0;darksithis002#darkmist002-VirtualBox: ~/lab1darksithis002#darkmist002-VirtualBox:~/lab1$ g++ -c homepg.cpp
homepg.cpp:14:26: error: expected class-name before ‘,’ token
homepg.cpp:15:1: error: expected class-name before ‘{’ token
homepg.cpp:18:24: error: ‘user’ was not declared in this scope
homepg.cpp:18:24: error: ISO C++ forbids initialization of member ‘userName1’ [-fpermissive]
homepg.cpp:18:24: error: making ‘userName1’ static [-fpermissive]
homepg.cpp:18:24: error: invalid in-class initialization of static data member of non-integral type ‘std::string {aka std::basic_string<char>}’
homepg.cpp:19:19: error: ISO C++ forbids initialization of member ‘counter’ [-fpermissive]
homepg.cpp:19:19: error: making ‘counter’ static [-fpermissive]
homepg.cpp:19:19: error: ISO C++ forbids in-class initialization of non-const static member ‘counter’
homepg.cpp:20:30: error: ‘friendList’ was not declared in this scope
homepg.cpp:20:30: error: ISO C++ forbids initialization of member ‘friends’ [-fpermissive]
homepg.cpp:20:30: error: making ‘friends’ static [-fpermissive]
homepg.cpp:20:30: error: invalid in-class initialization of static data member of non-integral type ‘std::vector<std::basic_string<char> >’
homepg.cpp:22:5: error: ‘cout’ does not name a type
homepg.cpp:23:5: error: ‘cout’ does not name a type
homepg.cpp:24:5: error: ‘cout’ does not name a type
homepg.cpp:29:26: error: ISO C++ forbids declaration of ‘displayHome’ with no type [-fpermissive]
homepg.cpp: In member function ‘int homepg::displayHome()’:
homepg.cpp:31:12: error: ‘messageBuff’ was not declared in this scope
homepg.cpp:45:6: error: ‘nextbrac’ was not declared in this scope
homepg.cpp:53:18: error: ‘userName’ was not declared in this scope
homepg.cpp:64:28: error: ‘friends’ was not declared in this scope
homepg.cpp:85:6: error: ‘count’ was not declared in this scope
]0;darksithis002#darkmist002-VirtualBox: ~/lab1darksithis002#darkmist002-VirtualBox:~/lab1$ g++ -c messageBuffer.cpp
messageBuffer.cpp: In member function ‘void messageBuffer::postMessage()’:
messageBuffer.cpp:26:13: error: ‘user’ was not declared in this scope
messageBuffer.cpp: In member function ‘void messageBuffer::tweetMessage()’:
messageBuffer.cpp:45:17: error: ‘user’ was not declared in this scope
]0;darksithis002#darkmist002-VirtualBox: ~/lab1darksithis002#darkmist002-VirtualBox:~/lab1$ exit
exit
Script done on Sun 29 Sep 2013 02:29:16 PM CDT
as a test, i put 2 of my classes together, one that compiled fine on it's own, and one that needed a function/variable from the other class, and tried to compile, and they compiled fine as
class a {
*functions and variables for a* }
class b {
a A;
*functions for b* }
class b in this example just doesn't work if i have it in a separate file in the same directory trying to call a, it gives me the errors i got in the script i made.
EDIT2: i'm also getting an error in the test file if i put in a main function and have it call functions from class a and b. (i know this error is from not declaring the functions, but if i try to declare them in their class, they give me another error which is: type::functionname cannot be overloaded, but if i take out the declaration both a and b compile fine and b can use a's functions, so why is it that they can fine without function declartions but a main function can't? and where do i put the declarations for the functions if i can't have them in the classes since it says it can't overload them?)

Answer 1

First of all - you only need to write "public:" once and then everything after that is public (until you write "private:" or similar).
Second - your firt "class b" seems to be the correct one.
Third - are both classes written in the same file? Or in different files? If in differebt files - did you include the file for a in the file for b? Are they .h files or .cc files?
Edit: here's how it should be, lets say a single file for now:
one file, main.cc:
#include <string>
#include <vector>
#include <iostream>
using namespace std;
class a {
string user;
public:
string user2;
vector<string> friendList;
void userName()
{
cout <<"blah blah"<<endl;
cin >> user;
}
void addFriend()
{
cout <<"blah blah"<<endl;
cin >> user2;
friendList.push_back(user2);
}
string getName()
{
return user;
}
};
class b {
string message, username;
a User;
public:
void postMessage()
{
cout <<"blah blah"<<endl;
getline(cin, message);
username = User.getName();
}
};
int main(){
b test;
test.postMessage();
}
There are many issues with your classes obviously - but this should compile at least.

Answer 2

Here are some hints to get you moving!
Define one class per file, and wrap header files (*.h) in include guards.
File a.h
#ifndef A_H
#define A_H
#include <string>
#include <vector>
#include <iostream>
class a // This class needs a better name!
{
private: // Class members are private by default but it's best to be explicit
std::string user; // When using classes from the C++ Standard Library in a
// header file, specify the `std` namespace explicitly
public: // Everything below here is public
std::vector<std::string> friendList;
void userName()
{
std::cout << "User name: "; // Note the use of `std::` here otherwise you'll see
// ‘cout’ does not name a type
std::cin >> user;
}
void addFriend()
{
std::cout << "Add friend: ";
std::string user2;
std::cin >> user2;
friendList.push_back(user2);
}
std::string getName()
{
return user;
}
};
#endif
File b.h
#ifndef B_H
#define B_H
#include <string>
#include <iostream>
#include "a.h" // Tell the pre-processor to include the entire contents of `a.h`,
// so that the code below knows what `class a` is.
class b
{
private:
std::string message, username;
a User;
public:
void postMessage()
{
std::cout << "Post Message: ";
std::getline(std::cin, message);
username = User.getName();
}
};
#endif
File main.cpp
This is the only file you need to compile, since it includes b.h (and a.h within that).
#include "b.h"
int main()
{
b my_b;
my_b.postMessage();
}
In the code above, like "Way 1", class b contains an instance of class a.
If you wished class b to extend class a, like "Way 2", you would use something like this:
class b: public a
{
// [...]
public:
void postMessage()
{
std::cout << "Post Message: ";
std::getline(std::cin, message);
username = getName();
}
};
To compile
Either use the terminal:
g++ -I/usr/local/include -Wall -Wextra -pedantic main.cpp -o main
Or use a Vim Script like SingleCompile.