wierd pointer behavior

mIXpRo (24)
hi ,
i wrote this function :
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
 
PlayerResult playerGetInstruments(Player player, Instrument** instruments,
		int* amount) {
	if (player == NULL || amount == NULL ) {
		return PLAYER_NULL_ARG;
	}
	int indexLast = 0;
	indexLast = getInstrumentsCount(player);
	if(indexLast <=0){
		return PLAYER_INSTRUMENT_AMOUNT_ERR;
	}
	if(*instruments!= NULL){
		free(*instruments);
	}
	(*instruments) = (Instrument*) malloc(sizeof(Instrument*) * indexLast);
	if ((*instruments) == NULL ) {
		return PLAYER_MEMORY_ERR;
	}
	PlayerResult result;
	if (!playerIsLegal(player, &result)) {
		free((*instruments));
		return result;
	}
	for (int i = 0; i < indexLast; i++) {
		instruments[i] = (Instrument*)malloc(sizeof(struct instrument_t));
		strcpy((*instruments[i]).name,player->instruments[i].name);
		strcpy((*instruments[i]).profession,player->instruments[i].profession);
	}
	*amount = indexLast;
	return PLAYER_SUCCESS;
}


and i tried testing it with this :
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
 
Player player=playerCreate("Nadav", "Peled", 2);
	Instrument* instruments, inst, inst2;
	instruments = NULL;
	int amount;
	strcpy(inst.name, "guitar");
	strcpy(inst.profession, "guitarist");
	strcpy(inst2.name, "bass");
	strcpy(inst2.profession, "bassist");
	PlayerResult res=playerAddInstrument(player, inst);
	res=playerAddInstrument(player, inst2);


	//Chcking func with legal inputs
	res=playerGetInstruments(player, &instruments, &amount);
	ASSERT(res==PLAYER_SUCCESS);
	ASSERT(amount==2);
	ASSERT((strcmp(instruments[0].name, inst.name)==0) &&
			(strcmp(instruments[1].name, inst2.name)==0));


my problem is when running in eclipse until the line
return PLAYER_SUCCESS

the stack seems ok meaning 
1
2
3
4
 
instruments[0].name = "guitar"
instruments[0].profession = "guitarist"
instruments[1].name = "bass"
instruments[1].profession = "bassist"


but when i return to the testing function (the second above)
i get in stack 
1
2
3
4
 
instruments[0].name = "guitar"
instruments[0].profession = "guitarist"
instruments[1].name = "i\0\0\0\0bass"
instruments[1].profession = "\0\0\0\0bassist"


and i tried adding more instruments then i got :
1
2
 
instruments[2].name = "\0\0\0\0i\0\0\0\0XXXX"
instruments[2].profession = "\0\0\0\0\0\0\0\0XXXXXX"


its like it's adding every time 4 bytes
why is that ???

thnx
Last edited on
kbw (9488)
That seems a little confused to me.

In:
 
 
PlayerResult playerGetInstruments(Player player, Instrument** instruments, int* amount)
you should think of instruments as a pointer passed by reference.

With that in mind, this is a reasonable statement:
 
 
(*instruments) = (Instrument*) malloc(sizeof(Instrument*) * indexLast);
but this isn't:
1
2
3
4
5
 
	for (int i = 0; i < indexLast; i++) {
		instruments[i] = (Instrument*)malloc(sizeof(struct instrument_t));
		strcpy((*instruments[i]).name,player->instruments[i].name);
		strcpy((*instruments[i]).profession,player->instruments[i].profession);
	}


Also, don't use malloc in C++ unless there's a specific good reason to.
mIXpRo (24)
can you please explain what do you mean by unreasonable statement .
Last edited on
kbw (9488)
You're treating it as an array of Instrument*, which it clearly isn't.
Topic archived. No new replies allowed.