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Function and function call? [Solved]

 
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Guest
Function and function call? [Solved]
PostPosted: Sun Sep 06, 2009 2:42 am     Reply with quote
Hi

I want to pass a pointer to the var "pos" in the function call and then use the struct in the other function...

It is a small test program only for the problem. It look like I can't use the &pos in the function caller?

It compile but doesn't print the right things. Tested in "MPLAB"

Code:
typedef struct {
 int8 x,y;
} _pos;

_pos pos;

//param pxy is a pointer to pos.
void testpos1(_pos *pxy){
 int8 out;

 out=pxy.x; //not working
 printf("%u\n",out);
}

void testpos(){
 pos.x=10;
 pos.y=20;
 printf("pos.x:%u\n",pos.x);
 printf("pos.y:%u\n",pos.y);
 testpos1(&pos); //what is wrong here?
}

Hints:-)
Guest
Function Pointer fali.
PostPosted: Sun Sep 06, 2009 2:52 am     Reply with quote
Hi

Sorry I found the solution:
If I use this in the function it work:-)
Code:
out=pxy->x
Ttelmah
Guest
PostPosted: Sun Sep 06, 2009 4:02 am     Reply with quote
Glad you found it.

It is however perhaps worth 'thinking' about using one of the old 'help you' strategies to avoid this in future. It is common for people who regularly use pointer in functions etc., to deliberately give them a distinct 'class' of names. So (for example), reseve the letter 'p' as a first letter on your function names, and only give variables that are pointers a name beginning with this letter or use a longer indicater like 'ptr'. So if you called your variable in the function:

ptr_pxy

It becomes 'plain' that this is a pointer, and needs to be dereferenced to access the internal values, with:

ptr_pxy->x

or

*(ptr_pxy).x

This is just a useful 'strategy' to avoid this type of problem, especially when programs get larger...

Best Wishes
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