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Use a class as a variable type in another class / include file.

P: n/a
Hello. I am quite new to the c++ language, and am still trying to
learn it. I recently discovered how using include files would allow me
to split up my code into smaller segments, instead of having class
definitions etc. in one big file (yay, major discovery...).

My problem is this:

When I define a class in one include file, and then try to instantiate
it in another, I get compile-time errors saying the type is invalid.
If i move the class definition of the class which instantiates the
other class into the main .cpp-file i get no errors.

How to solve this problem? I would like to have each class in seperate
include files, but still be able to instantiate them inside each
other.

I am using Microsoft Visual C++ 6.0 on Windows XP.

-Toke
Jul 22 '05 #1
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10 Replies


P: n/a
"Toke H?iland-J?rgensen" <to**@toke.dk> wrote...
Hello. I am quite new to the c++ language, and am still trying to
learn it. I recently discovered how using include files would allow me
to split up my code into smaller segments, instead of having class
definitions etc. in one big file (yay, major discovery...).

My problem is this:

When I define a class in one include file, and then try to instantiate
it in another, I get compile-time errors saying the type is invalid.
If i move the class definition of the class which instantiates the
other class into the main .cpp-file i get no errors.
Try including the header with the first class into the source code
with the other class:

#include "myheader.h"

How to solve this problem? I would like to have each class in seperate
include files, but still be able to instantiate them inside each
other.


Also, see "forward declaration", it might be relevant, but hard to
tell without the code.

Victor
Jul 22 '05 #2

P: n/a
"Toke H?iland-J?rgensen" <to**@toke.dk> wrote in message
news:59**************************@posting.google.c om...
Hello. I am quite new to the c++ language, and am still trying to
learn it. I recently discovered how using include files would allow me
to split up my code into smaller segments, instead of having class
definitions etc. in one big file (yay, major discovery...).

My problem is this:

When I define a class in one include file, and then try to instantiate
it in another, I get compile-time errors saying the type is invalid.
If i move the class definition of the class which instantiates the
other class into the main .cpp-file i get no errors.

How to solve this problem? I would like to have each class in seperate
include files, but still be able to instantiate them inside each
other.

I am using Microsoft Visual C++ 6.0 on Windows XP.

-Toke


I would suggest something like this:

// main.cpp
#include "myclass.h"
int main() {// make use of myclass here}
// end of file

in one file,

// myclass.h
#if !defined MYCLASS_H
#define MYCLASS_H
class CoolClass
{
public:
CoolClass();
void amethod();
// other stuff
};
#endif // end of file

and finally

// myclass.cpp
#include "myclass.h"
CoolClass::CoolClass()
{
// define constructor here
}
void CoolClass::amethod()
{
// define amethod here
}
// end of file

main.cpp and myclass.cpp would be compiled into your project and myclass.h
put into your include path.

--
Cy
http://home.rochester.rr.com/cyhome/
Jul 22 '05 #3

P: n/a
"Cy Edmunds" <ce******@spamless.rochester.rr.com> wrote in message news:<6A*******************@twister.nyroc.rr.com>. ..

I would suggest something like this:
<snip>
main.cpp and myclass.cpp would be compiled into your project and myclass.h
put into your include path.
This is the structure I have been able to put together myself, and it
works fine, just like you suggested. My problem is using myclass in
another include file, e.g. myotherclass.cpp

building on your structure: // main.cpp
#include "myclass.h"
int main() {// make use of myclass here}
// end of file

in one file,

// myclass.h
#if !defined MYCLASS_H
#define MYCLASS_H
class CoolClass
{
public:
CoolClass();
void amethod();
// other stuff
};
#endif // end of file

and finally

// myclass.cpp
#include "myclass.h"
CoolClass::CoolClass()
{
// define constructor here
}
void CoolClass::amethod()
{
// define amethod here
}
// end of file


another class:

//myotherclass.h
#if !defined MYOTHERCLASS_H
#define MYOTHERCLASS_H
class QuiteCoolClass
{
public:
QuiteCoolClass();
void amethod();
// other stuff
};
#endif // end of file

//myotherclass.cpp

#include "myotherclass.h"
QuiteCoolClass::QuiteCoolClass()
{
// define constructor here
}
void QuiteCoolClass::amethod()
{
CoolClass coolClassInstance; //this is where the error is
coolClassInstance.amethod(); //this doesn't work either
// define amethod here
}
// end of file

I get compile time errors when trying to do the above, whereas
instantiating CoolClass in main() gives me no problems whatsoever,
i.e. if I move the code from myotherclass.h and myotherclass.cpp into
main.ccp, i get no errors.

I hope this clarifies my problem a little... :)

-Toke
Jul 22 '05 #4

P: n/a
"Victor Bazarov" <v.********@comAcast.net> wrote in message news:<r55Ib.72445$VB2.142131@attbi_s51>...
the
Try including the header with the first class into the source code
with the other class:

#include "myheader.h"
I tried that to no avail...
Also, see "forward declaration", it might be relevant, but hard to
tell without the code.


I googled and found this document about forward declarations:
http://www.adp-gmbh.ch/cpp/forward_decl.html
I (think) i did what it suggests, but that didn't help either.

Would it help if I posted the sourcecode of the offending files here?

-Toke
Jul 22 '05 #5

P: n/a
"Toke H?iland-J?rgensen" <to**@toke.dk> wrote...
"Victor Bazarov" <v.********@comAcast.net> wrote in message news:<r55Ib.72445$VB2.142131@attbi_s51>... the
Try including the header with the first class into the source code
with the other class:

#include "myheader.h"


I tried that to no avail...
Also, see "forward declaration", it might be relevant, but hard to
tell without the code.


I googled and found this document about forward declarations:
http://www.adp-gmbh.ch/cpp/forward_decl.html
I (think) i did what it suggests, but that didn't help either.

Would it help if I posted the sourcecode of the offending files here?


Most certainly, yes. However, don't attach it, copy-and-paste it. Also,
remove all non-essential parts of the code and make sure that after that
it still compiles with exactly the same error message as you claim it does.

V
Jul 22 '05 #6

P: n/a
"Victor Bazarov" <v.********@comAcast.net> wrote in message news:<EPqIb.11490$I07.23677@attbi_s53>...
Most certainly, yes. However, don't attach it, copy-and-paste it. Also,
remove all non-essential parts of the code and make sure that after that
it still compiles with exactly the same error message as you claim it does.


Okay...the program is an attempt at making a text adventure as an
excercise...

//adventure.cpp
#include <iostream.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fstream.h>
#include <windows.h>

const int WEAPON = 100;
const int ARMOR = 101;
const int CHARM = 102;
const int TEXTMODE = 200;
const int BINARYMODE = 201;
const int NUMRANDOMS = 10000;
const int EAST = 1;
const int WEST = 2;
const int NORTH = 3;
const int SOUTH = 4;

#include "random.h"
#include "DataHandler.h"
#include "TreasureChest.h"

using namespace adventure;

RandomHandler randomBase;

TreasureChest treasureChest;

int main()
{
return 0;
}

//random.h

#ifndef __random_h__

#define __random_h__

namespace adventure
{
const int NUMRANDOMS = 10000;

//
// RandomHandler class
// used to store a bunch of randoms...used as a workaround
//

class RandomHandler
{
int randoms[NUMRANDOMS];
int randomCounter;

public:
RandomHandler();
int GetRandom();
};

}
#endif
//random.cpp
#include "random.h"
#include <stdlib.h>
#include <time.h>
namespace adventure
{

RandomHandler::RandomHandler()
{
int i;
srand( (unsigned)time( NULL ) );

for( i = 0; i < NUMRANDOMS; i++ )
randoms[i] = rand();

randomCounter = 0;
}

int RandomHandler::GetRandom()
{
randomCounter++;
if(randomCounter >= NUMRANDOMS)
randomCounter = 0;

return randoms[randomCounter];
}
}

//DataHandler.h / DataHandler.cpp defines the class DataHandler
//They work fine, however, so i excluded them...

//TreasureChest.h
#ifndef __TreasureChest_h__
#define __TreasureChest_h__

#include "DataHandler.h"

namespace adventure
{
class DataHandler;
class RandomHandler;

//
// Treasure struct.
// Contains information about treasure.
//
struct Treasure {
char name [50];
int isWearable;
int gold, hBonus, sBonus, aBonus;
char type;
int attackModifier, defenceModifier;
};

//
// TreasureChest class
// Manages treasures.
//
class TreasureChest
{
Treasure * treasures;
Treasure emptyTreasure;
int numTreasures;
void AddTreasure(Treasure);
void LoadTreasures();

public:
TreasureChest();
Treasure GetTreasure(int);
};
}

#endif

//TreasureChest.cpp
#include "TreasureChest.h"
#include "DataHandler.h"
#include <string.h>
#include <stdlib.h>
namespace adventure
{

const int TEXTMODE = 200;
const int BINARYMODE = 201;

TreasureChest::TreasureChest()
{
numTreasures = 0;
treasures = new Treasure[1];
strcpy(emptyTreasure.name, "No treasure");
LoadTreasures();
}

void TreasureChest::AddTreasure(Treasure add)
{

treasures = (Treasure *) realloc(treasures, (numTreasures+1) *
sizeof(Treasure));
treasures[numTreasures] = add;
numTreasures++;
}

void TreasureChest::LoadTreasures()
{
char input[100] = "";
Treasure thisTreasure;
DataHandler treasureGet ("treasure.txt",TEXTMODE);

while(treasureGet.GetLine(input) != false) {
if(input[0] != '#') {
strcpy(thisTreasure.name,strtok(input, ";"));
thisTreasure.isWearable = atoi(strtok(NULL, ";"));
thisTreasure.type = atoi(strtok(NULL, ";"));
thisTreasure.gold = atoi(strtok(NULL, ";"));
thisTreasure.hBonus = atoi(strtok(NULL, ";"));
thisTreasure.sBonus = atoi(strtok(NULL, ";"));
thisTreasure.aBonus = atoi(strtok(NULL, ";"));
thisTreasure.attackModifier = atoi(strtok(NULL, ";"));
thisTreasure.defenceModifier = atoi(strtok(NULL, ";"));

AddTreasure(thisTreasure);
}
}

}

Treasure TreasureChest::GetTreasure(int type)
{
int t;
double r;

do {
r = ( (double) randomBase.GetRandom() / (double)(RAND_MAX+1) );
//class instantiated in adventure.cpp - problem
t = (int) (r * numTreasures);
} while(treasures[t].type != type);
return treasures[t];
}

}
The compiler errors:
--------------------Configuration: adventure - Win32
Debug--------------------
Compiling...
TreasureChest.cpp
d:\dokumenter\coding\adventure\treasurechest.cpp(6 0) : error C2065:
'randomBase' : undeclared identifier
d:\dokumenter\coding\adventure\treasurechest.cpp(6 0) : error C2228:
left of '.GetRandom' must have class/struct/union type
adventure.cpp
DataHandler.cpp
Error executing cl.exe.

adventure.exe - 2 error(s), 0 warning(s)

I put in comments where the errors are. Hope this helps... :)

-Toke
Jul 22 '05 #7

P: n/a

"Toke H?iland-J?rgensen" <to**@toke.dk> wrote in message news:59**************************@posting.google.c om...
#include <iostream.h>
#include <fstream.h>
Get in the habit of using standard constructs. The include files are <iostream> and <fstream>.

const int WEAPON = 100;
const int ARMOR = 101;
const int CHARM = 102;
const int TEXTMODE = 200;
const int BINARYMODE = 201;
const int NUMRANDOMS = 10000;
const int EAST = 1;
const int WEST = 2;
const int NORTH = 3;
const int SOUTH = 4;
You might consider grouping these into enums for convenience:
enum Item { WEAPON, ARMOR, CHARM };
enum Direction { EAST, WEST, NORTH, SOUTH } ; .
etc..
#ifndef __random_h__

#define __random_h__
Do not use symbols like this in your program. They are reserved for the compiler
implementors.

#ifndef INCLUDE_RANDOM_H
#define INCLUDE_RANDOM_H
strcpy(thisTreasure.name,strtok(input, ";"));
thisTreasure.isWearable = atoi(strtok(NULL, ";"));
strtok and atoi are both evil functions. atoi exhibits undefined behavior if
you give it data outside the range. strtok is a piece of crap that has no
business ever getting standardized. You do know that it writes over
the input string (in addition to storing internal state).

I'm not clear why you just didn't use a strea and formatted I/O here. It
would have been much easier.
r = ( (double) randomBase.GetRandom() / (double)(RAND_MAX+1) );
//class instantiated in adventure.cpp - proble


Because randomBase hasn't been seen in this file. You define it in main and there's no
declaration for it elsewhere. You probably want to put
extern RandomHandler randomBase
in one of the include files.
Jul 22 '05 #8

P: n/a
"Toke H?iland-J?rgensen" <to**@toke.dk> wrote in message
news:59**************************@posting.google.c om...
"Victor Bazarov" <v.********@comAcast.net> wrote in message news:<EPqIb.11490$I07.23677@attbi_s53>...
Most certainly, yes. However, don't attach it, copy-and-paste it. Also, remove all non-essential parts of the code and make sure that after that
it still compiles with exactly the same error message as you claim it

does.
Okay...the program is an attempt at making a text adventure as an
excercise...

//adventure.cpp
#include <iostream.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fstream.h>
#include <windows.h>

const int WEAPON = 100;
const int ARMOR = 101;
const int CHARM = 102;
const int TEXTMODE = 200;
const int BINARYMODE = 201;
const int NUMRANDOMS = 10000;
const int EAST = 1;
const int WEST = 2;
const int NORTH = 3;
const int SOUTH = 4;

#include "random.h"
#include "DataHandler.h"
#include "TreasureChest.h"

using namespace adventure;

RandomHandler randomBase;

TreasureChest treasureChest;

int main()
{
return 0;
This looks like kind of a short adventure. :)
}

//random.h

#ifndef __random_h__

#define __random_h__

namespace adventure
{
const int NUMRANDOMS = 10000;

//
// RandomHandler class
// used to store a bunch of randoms...used as a workaround
//

class RandomHandler
{
int randoms[NUMRANDOMS];
int randomCounter;

public:
RandomHandler();
int GetRandom();
};

}
#endif
//random.cpp
#include "random.h"
#include <stdlib.h>
#include <time.h>
namespace adventure
{

RandomHandler::RandomHandler()
{
int i;
srand( (unsigned)time( NULL ) );

for( i = 0; i < NUMRANDOMS; i++ )
randoms[i] = rand();

randomCounter = 0;
}

int RandomHandler::GetRandom()
{
randomCounter++;
if(randomCounter >= NUMRANDOMS)
randomCounter = 0;

return randoms[randomCounter];
}
}

//DataHandler.h / DataHandler.cpp defines the class DataHandler
//They work fine, however, so i excluded them...

//TreasureChest.h
#ifndef __TreasureChest_h__
#define __TreasureChest_h__

#include "DataHandler.h"

namespace adventure
{
class DataHandler;
class RandomHandler;

//
// Treasure struct.
// Contains information about treasure.
//
struct Treasure {
char name [50];
int isWearable;
int gold, hBonus, sBonus, aBonus;
char type;
int attackModifier, defenceModifier;
};

//
// TreasureChest class
// Manages treasures.
//
class TreasureChest
{
Treasure * treasures;
Treasure emptyTreasure;
int numTreasures;
void AddTreasure(Treasure);
void LoadTreasures();

public:
TreasureChest();
Treasure GetTreasure(int);
};
}

#endif

//TreasureChest.cpp
#include "TreasureChest.h"
#include "DataHandler.h"
#include <string.h>
#include <stdlib.h>
namespace adventure
{

const int TEXTMODE = 200;
const int BINARYMODE = 201;

TreasureChest::TreasureChest()
{
numTreasures = 0;
treasures = new Treasure[1];
strcpy(emptyTreasure.name, "No treasure");
LoadTreasures();
}

void TreasureChest::AddTreasure(Treasure add)
{

treasures = (Treasure *) realloc(treasures, (numTreasures+1) *
sizeof(Treasure));
treasures[numTreasures] = add;
numTreasures++;
}

void TreasureChest::LoadTreasures()
{
char input[100] = "";
Treasure thisTreasure;
DataHandler treasureGet ("treasure.txt",TEXTMODE);

while(treasureGet.GetLine(input) != false) {
if(input[0] != '#') {
strcpy(thisTreasure.name,strtok(input, ";"));
thisTreasure.isWearable = atoi(strtok(NULL, ";"));
thisTreasure.type = atoi(strtok(NULL, ";"));
thisTreasure.gold = atoi(strtok(NULL, ";"));
thisTreasure.hBonus = atoi(strtok(NULL, ";"));
thisTreasure.sBonus = atoi(strtok(NULL, ";"));
thisTreasure.aBonus = atoi(strtok(NULL, ";"));
thisTreasure.attackModifier = atoi(strtok(NULL, ";"));
thisTreasure.defenceModifier = atoi(strtok(NULL, ";"));

AddTreasure(thisTreasure);
}
}

}

Treasure TreasureChest::GetTreasure(int type)
{
int t;
double r;

do {
r = ( (double) randomBase.GetRandom() / (double)(RAND_MAX+1) );
//class instantiated in adventure.cpp - problem
t = (int) (r * numTreasures);
} while(treasures[t].type != type);
return treasures[t];
}

}
The compiler errors:
--------------------Configuration: adventure - Win32
Debug--------------------
Compiling...
TreasureChest.cpp
d:\dokumenter\coding\adventure\treasurechest.cpp(6 0) : error C2065:
'randomBase' : undeclared identifier
d:\dokumenter\coding\adventure\treasurechest.cpp(6 0) : error C2228:
left of '.GetRandom' must have class/struct/union type
adventure.cpp
DataHandler.cpp
Error executing cl.exe.

adventure.exe - 2 error(s), 0 warning(s)

I put in comments where the errors are. Hope this helps... :)

-Toke


OK, randomBase is a global variable defined in adventure.cpp. Then you try
to use it in TreasureChest.cpp. Since that symbol isn't defined in that
file, the compiler says, "undeclared identifier". That makes sense. The
other error is spurious, trying to keep going without knowing what
randomBase means.

So how to fix it? You could declare randomBase external, but that would be a
poor idea. I suggest you avoid global variables as much as possible. In this
case I would suggest randomBase be declared in your main function and passed
as an argument as needed; e.g.

Treasure TreasureChest::GetTreasure(int type, RandomHandler &randomBase)

--
Cy
http://home.rochester.rr.com/cyhome/
Jul 22 '05 #9

P: n/a
"Cy Edmunds" <ce******@spamless.rochester.rr.com> wrote in message news:<SA*******************@twister.nyroc.rr.com>. ..
So how to fix it? You could declare randomBase external, but that would be a
poor idea. I suggest you avoid global variables as much as possible. In this
case I would suggest randomBase be declared in your main function and passed
as an argument as needed; e.g.

Treasure TreasureChest::GetTreasure(int type, RandomHandler &randomBase)


Ok, I will change my code to pass the global variables around as you
suggested. It makes sense to do so instead of using global variables.
Thanks alot for your help... :)

-Toke
Jul 22 '05 #10

P: n/a
"Ron Natalie" <ro*@sensor.com> wrote in message news:<3f***********************@news.newshosting.c om>...
strtok and atoi are both evil functions. atoi exhibits undefined behavior if
you give it data outside the range. strtok is a piece of crap that has no
business ever getting standardized. You do know that it writes over
the input string (in addition to storing internal state).

I'm not clear why you just didn't use a strea and formatted I/O here. It
would have been much easier.

Thank you for your suggestions to improve my code.

I'm afraid I don't know what 'strea and formatted I/O' is. I'd
appreciate if you'd point me to a link describing it, or perhaps
descibe it yourself... :)

-Toke
Jul 22 '05 #11

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