Help with Steve Summit's tutorial

**glo** · 05-16-2006

Hi there,
Just finished his beginner's c tutorials, which were very helpful, and got on to intermediate.
I am now trying my luck with the second week's Assignment (Link) but running into some trouble: I do what is asked in the first exercise, without understanding much of what I am doing, but no matter what I try I can't compile it. The source, by the way, was provided. Heres a screen of the problem: Screenshot
So what am I missing? has anyone succeeded in this exercise? Can it be a problem with the source?

- I use cygwin

Thanks.

**swgh** · 05-16-2006

I do C++, but I have seen this error before. It says actor is undifined, meaning either you have not decared it in main or you have forgoten to extern link it to main from another file. If actor is in another header file, make sure it is included in the main file. Another alternative is to use the debugger to step through the complation process and see what is going wrong. But if you have delcared actor in main, is is spelt correctly? Remeber both C and C++ is case sensitive. If this is not the answer, perhaps somthing is wrong with the code in the tutorial

**glo** · 05-16-2006

Yes, the actor structure is declared in another header file, but is linked and included.

Code:

$ make -f makefile.unix
gcc    -c -o commands.o commands.c
gcc    -c -o getliner.o getliner.c
gcc    -c -o getwords.o getwords.c
gcc    -c -o main.o main.c
main.c: In function `main':
main.c:34: error: `actor' undeclared (first use in this function)
main.c:34: error: (Each undeclared identifier is reported only once
main.c:34: error: for each function it appears in.)
make: *** [main.o] Error 1

Though it still says something is wrong.
If anyone managed this exercise Id like to know if he ran into the same problem please.

Thanks.

**quzah** · 05-16-2006

Are you #include-ing the header file it's declared in? You have to.

Quzah.

**glo** · 05-17-2006

Yes, it is included:

Code:

#include <stdio.h>
#include <stdlib.h>
#include "game.h"
#include "utils.h"
#include "defs.h"

This is how it is declared in game.h:

Code:

struct actor
    {
    struct room *location;
    struct object *contents;    /* possessions */
    };

And this is the makefile:

Code:

CC = gcc

OBJS = commands.o getliner.o getwords.o main.o object.o parser.o rooms.o

game: $(OBJS)
	$(CC) -o $@ $(OBJS)

commands.o: commands.c game.h defs.h
getliner.o: getliner.c utils.h
getwords.o: getwords.c utils.h
main.o: main.c game.h utils.h
object.o: object.c game.h defs.h
parser.o: parser.c defs.h game.h utils.h
rooms.o: rooms.c game.h defs.h

**quzah** · 05-17-2006

Are you using the keyword 'struct' before 'actor' in your usage of it? C isn't C++. This is legal:

Code:

struct actor x;
...
void foo( struct actor ); /* a function prototype */
...
void foo( struct actor a ) /* a function definition... */
{
    ...
}

This isn't:

Code:

actor x;
...
foo( actor );
...
foo( actor a )
{
    ...
}

Quzah.

**glo** · 05-17-2006

Quite interestingly there is a line using, what may seem, an ilegal use of the struct:

Code:

if(!readdatafile())
        exit(1);

    gotoroom(&actor, getentryroom());    /* put actor in initial room */

Could this be it?

Its definition, by the way, is:

Code:

int
gotoroom(struct actor *actor, struct room *room)
{
actor->location = room;
return TRUE;
}

**quzah** · 05-17-2006

What is 'actor' in that reference? Have you declared a variable instance prior to that called 'actor'? Something like...

Code:

struct actor actor;
...
gotoroom( &actor, getentryroom( ) );

Quzah.

**glo** · 05-17-2006

Well there is this decleration in main.c:

Code:

static struct actor player;

But the structure definition should be prior to it, it is included just before it.
I hope Im getting it right, all I did was follow the instructions he provided and paste bits of code into source code files he provided as well. (you can check the exercise linked in the first post)

**quzah** · 05-17-2006

You should be passing the variable 'player' then instead of 'actor'. This is why it's a bad idea to name your variable instances the same thing as the structure tag.

Code:

struct actor actor; /* bad */
struct actor player; /* un-bad */

Code:

int
gotoroom(struct actor *actor, struct room *room)
{
actor->location = room;
return TRUE;
}

[/quote]

Quzah.

**glo** · 05-17-2006

Woo! thanks!

Apparently this was not the only problem with this exercise:

"After adding all the new code, and any necessary prototype declarations to game.h, the program should again compile and run"

Made me believe it should compile after following his instructions, but in reality, other than the error you mentioned, I also had to edit makefile.unix (this process wasnt tutored yet either).

Anyway all is good now, thanks.
If anyone ever comes across this tutorial make sure to fix these problems.

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