C Style Question

RevertTS · 2006-12-27 07:27:45

While programming a stack in C, I saw an example where the pop method was void and a pointer was passed to it. I thought this was a little weird, because my first instinct would be to just return a pointer. I was wondering if this was common practice or if one of these methods was considered more appropriate than the other.

As an example of the two styles I'm talking about:

  1 #include <stdio>
  2 
  3 int *foo1(int in);
  4 void foo2(int in, int *ptr);
  5 
  6 int main(void){
  7    int *ptr, *ptr2, in = 5;
  8    
  9    ptr = foo1(in);
 10    foo2(in, ptr2);
 11    
 12    printf("%d  %d n", *ptr, *ptr2);
 13 }  
 14 
 15 int *foo1(int in){
 16    int *ptr;
 17    *ptr = (in + 2);
 18 
 19    return ptr;
 20 }
 21 
 22 void foo2(int in, int *ptr){
 23    *ptr = (in + 2);
 24 }

Also, is it possible to return the address of a local variable? I ran into this example:

typedef struct {float x,y,z;} COORD;
 
         main()
 
          {  COORD p1, *coord_fn();
                        /* declare fn to return ptr of
                         COORD type */ 
 
                         ....
                         p1 = *coord_fn(...);
                 /* assign contents of address returned */
                         ....
                 }

   COORD *coord_fn(...)
 
          {  COORD p;
                         .....
                         p = ....;
                         /* assign structure values */ 
 
                         return &p;
                         /* return address of p */
                 }

But when I did something similar to test it, it threw a warning:

warning: function returns address of local variable

Is there a way to bypass these warnings with the compiler?

Thanks guys.

chrismortimore · 2006-12-27 09:38:55

If you pass the address of a local variable, then (as far as I know) it won't work, as when the function ends, the variable is no longer there. You could do this, and it should work:

COORD *coord_fn(COORD *p,...)
{
        p = ...;
        .......
        return &p;
}

If it doesn't, I'm blaming being tired

As for returning void and passing a pointer, I personally prefer this to returning a pointer. But it took me a while to get used to it...

Arch Linux

#1 2006-12-27 07:27:45

C Style Question

#2 2006-12-27 09:38:55

Re: C Style Question

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