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Topic Starter Topic: Pointers pissing me off
Eraser
Cool #9
Cool #9
Joined: 01 Dec 2000
Posts: 44138
PostPosted: 12-09-2011 05:20 AM           Profile   Send private message  E-mail  Edit post Reply with quote


I'm not much of a C programmer because my grasp of pointers is still flimsy at best.
So I have the following situation right now. In cgame, I have the following function:

Code:
qboolean CG_DrawSinglePlayerObjectives( void ) {
   int i;
   vec4_t color;
   playerscore_t *scores;
   
   
   //q3w: there's a bunch of unrelated stuff here
   
   
   //draw level score
   COM_CalculatePlayerScore( scores, cg.snap->ps.persistant, CG_GetAccuracy(), CG_GetSkill() );

    //q3w: the bits below aren't really important right now
   i = strlen(va("%i", scores->totalScore));
   CG_DrawBigStringColor( 496 - (i * BIGCHAR_WIDTH), 343, va("%i", scores->totalScore), color);   

   if ( ++cg.deferredPlayerLoading > 10 ) {
      CG_LoadDeferredPlayers();
   }

   return qtrue;
}


The playerscore_t struct is defined in q_shared.h like this:

Code:
typedef struct playerscore_s {
   int carnageScore;
   int accuracy;
   int accuracyScore;
   int deaths;
   int deathsScore;
   int secretsFound;
   int secretsCount;
   int secretsScore;
   int subtotalScore;
   float skill;
   float skillModifier;
   int skillScore;
   int totalScore;
} playerscore_t;


In q_shared.c, the COM_CalculatePlayerScore function is defined. Right now, all it does is set the carnageScore variable in the struct to 0:

Code:
void COM_CalculatePlayerScore(playerscore_t *scores, int persistant[MAX_PERSISTANT], int accuracy, float skill) {
   scores->totalScore = 0;
}


So far so good, this appears to work well.
I also have another function which calls the COM_CalculatePlayerScore function:

Code:
void CG_DrawSinglePlayerIntermission( void ) {
   vec4_t color;
   playerscore_t *scores;
   
   color[0] = 1;
   color[1] = 1;
   color[2] = 1;
   color[3] = 1;
   
   COM_CalculatePlayerScore( scores, cg.snap->ps.persistant, CG_GetAccuracy(), CG_GetSkill() );
}


When the intermission screen is supposed to be shown, however, the game crashes.
I modified the COM_CalculatePlayerScore function slightly to see what was happening:

Code:
void COM_CalculatePlayerScore(playerscore_t *scores, int persistant[MAX_PERSISTANT], int accuracy, float skill) {
   if (score) {
      Com_Printf("Yes\n");
      scores->totalScore = 0;
   } else {
      Com_Printf("No\n");
   }
}


Now when displaying the objectives (the function that went right), it simply outputs a lot of "yes"-es in the console and it works well. However, when the intermission screen needs to be shown, it outputs a lot of "no"'s.
You may wonder why that color[0] = 1 etc is in there. Well, at one point I commented those out to have as little unrelated code in there as possible and that caused the game to go crashing again. I assume that "scores" inside the COM_CalculatePlayerScore was no longer NULL but also not a playerscore_t struct, but something else entirely (not sure what). I was pretty much dumbstruck to find that these seemingly unrelated lines of code could have such an impact.

So you see, I have no clue what I'm doing and it's starting to annoy me. Can any of you gurus point me in the right way?
Oh and one more thing, I tried to have my COM_CalculatePlayerScores return a playerscore_t struct as well as have it return a pointer to such a struct but I couldn't get either of those cases to work at all, so I figured passing a pointer argument to the method was the next best thing and that worked, until now.

This is what you get for coding in Java and C# too much :(

edit:
oh, I just commented out the stuff I had marked as "there's a bunch of unrelated stuff here" in the first function listed and now the game crashes when displaying the objectives as well :(
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^misantropia^
Mentor
Mentor
Joined: 12 Mar 2005
Posts: 3958
PostPosted: 12-09-2011 01:10 PM           Profile Send private message  E-mail  Edit post Reply with quote


Eraser wrote:
Code:
void CG_DrawSinglePlayerIntermission( void ) {
   vec4_t color;
   playerscore_t *scores;
   
   color[0] = 1;
   color[1] = 1;
   color[2] = 1;
   color[3] = 1;
   
   COM_CalculatePlayerScore( scores, cg.snap->ps.persistant, CG_GetAccuracy(), CG_GetSkill() );
}

You're passing an uninitialized scores pointer to COM_CalculatePlayerScore().
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Eraser
Cool #9
Cool #9
Joined: 01 Dec 2000
Posts: 44138
PostPosted: 12-10-2011 12:55 AM           Profile   Send private message  E-mail  Edit post Reply with quote


Should I use memset for that? I remember that crashing the whole thing as well, but I'll try again. But why does it work correctly in the other function then? I don't initialize it there either.
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Eraser
Cool #9
Cool #9
Joined: 01 Dec 2000
Posts: 44138
PostPosted: 12-10-2011 04:15 AM           Profile   Send private message  E-mail  Edit post Reply with quote


Whoa, I got it fixed.
I forgot to declare the COM_CalculatePlayerScore function in q_shared.h so I guess that messed it up. But when I realized this, I was halfway through rewriting the code so that COM_CalculatePlayerScore simply returns the struct (not a pointer to it) so that I don't have to pass a pointer to a struct to the method. I couldn't get the return-a-struct method working before but I guess that was due to the function not being declared in q_shared.h.
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