Pass object to constructor of another class

[cloonix]

For learning purpose i try following (text rpg context): I'm creating a Player object. Next i want to create a Monster object with passing the player object to that monster class. But i get a compilation error. I worked it out if I put everything in a single file. If i seperate my code into several header and source files i get the following compilation error:

$ g++ *.cpp
In file included from monster.cpp:1:0:
monster.h:7:17: error: expected ‘)’ before ‘&’ token
   Monster(Player& x);
                 ^
monster.h:9:3: error: ‘Player’ does not name a type
   Player& p;
   ^
monster.cpp:3:17: error: expected constructor, destructor, or type conversion before ‘(’ token
 Monster::Monster(Player& x)
                 ^
monster.cpp:4:9: error: expected unqualified-id before ‘{’ token
  : p{x} {

The code:

// main.cpp
#include "player.h"
#include "monster.h"

main () {
	Player player1("Meanman");
	Monster monster1(player1);
}

// player.h
#ifndef PLAYER_H
#define PLAYER_H
#include <string>

class Player {
	public:
		Player(std::string name);
	private:
		std::string playername;
};
#endif 

//player.cpp
#include "player.h"

Player::Player(std::string name)
	: playername{name} {
		
}

//monster.h
#ifndef MONSTER_H
#define MONSTER_H

class Monster {
	public:
		Monster(Player& x);
	private:
		Player& p;
};
#endif 

// monster.cpp
#include "monster.h"

Monster::Monster(Player& x)
	: p{x} {
		
}

Can you help me with that? What am I doing wrong?

Thanks for your time.

[helios]

//...
#define MONSTER_H

//The compiler needs to know that the identifier 'Player' refers to a type
//and not, say, a function.
class Player;

class Monster {
//... 

[TheIdeasMan]

Hi,

Just to help you out in the future:

g++ *.cpp

Always compile with a high level of warnings - warnings are your friend, they tell you about things that will probably cause problems one way or another. Including things that will cause runtime errors.

So try this instead, as a minimum always:

g++ -std=c++14 -Wall -Wextra -pedantic-errors -o ProgName

If you don't have a C++14 compliant compiler (don't see why you can't), then substitute -std=c++11. ProgName is the name you want your executable file to have. IMO this is better than the default a.out

Actually if you can get hold of the latest version of g++ (6.1), it defaults to -std=c++14.

There are even more very handy warnings that are not enabled by the above seemingly comprehensive options:

http://www.cplusplus.com/forum/general/183731/#msg899203

[jlb]

Actually if you can get hold of the latest version of g++ (6.1), it defaults to -std=c++14.

No it defaults to -std=gnu++14. If you want to disable the gcc hacks you still need to use the -std=c++14 flag and either the -pedantic or -pedantic-errors flag.

https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/Standards.html#Standards

[TheIdeasMan]

@jlb

No it defaults to -std=gnu++14.

That's a good point :+) It's best to be explicit about which standard one wants :+D

[cloonix]

@helios: Thanks a lot for the solution. Works.

@Others: Thanks for the hints. My g++ command was already an alias for -std=c++14 -ansi -Wpedantic. I will add -Wall and -Wextra. And i guess it's better to show the people here in the forum the options i'm using on compilation. Will not use alias anymore.

[TheIdeasMan]

One more thing:

-std=c++14 -ansi

is a conflict, -ansi means c++98. Although if you have that and c++14, I guess it will select the c++14


https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/C-Dialect-Options.html#C-Dialect-Options