指向结构数组的指针

Question

I'm trying to compare the variable dist between two nodes of my array of structures.

This is the structure:

struct arco{
  int u, v;
  double temp, dist; 
}arcos[MAXOASIS];

This is my code:

int compDist(const void *a, *void const *b, i, j){
  struct arco *ia = (struct arco *)a;
  struct arco *ib = (struct arco *)b;
  ia->arco[i].dist;
  ib->arco[j].dist;
  return(if(*ia > *ib)? *ia : *ib)
}

But it is wrong. How should it be done?

Answer 1

  ia->arco[i].dist;
  ib->arco[j].dist;

What is that supposed to do? You probably want something like

return(ia->arco[i].dist > ib->arco[j].dist? ia->arco[i].dist : ia->arco[j].dist)

You could use some intermediate variables to make it cleaner.

EDIT

In light of your edit it's likely you want:

return (ia->dist - ib->dist);

Answer 2

You are compairing pointer to strutcs rather then variables. I don't know your struct definition but I think you need something like:

return(if(ia->arco[i].dist > ib->arco[i].dist)? 1 : 0);

Answer 3

There are a lots of mistakes in your code, You were initially returning a structure pointer whereas your function declaration says int.

 struct arco *compDist(const void *a, *void const *b, i, j){
  struct arco *ia = (struct arco *)a;
  struct arco *ib = (struct arco *)b;
  return(if(ia->arco[i].dist > ib->arco[j].dist)? *ia : *ib)
}

Also a comparison like

if(*ia > *ib)

is invalid, you can't just compare two structures, in c++, you could overload the '>' operator but you can't do the same in c as far as i know.

That should work but i can't guarantee it as i have no idea how you've defined your structure arco.

Answer 4

arco is not a member of arco.

Instead of saying "it is wrong", post the compiler errors you are getting, and you will get better answers in return.