Thread: pointer to struct in function

Im trying to learn how to access a structre through using a pointer passed from one function to another ..

Code:

#include <stdio.h>
void proof( struct foo bar  *p){
  printf("%i\n",p->a);
}
int main( int argc, char * argv[] ){
  struct foo{
    int a;
  }bar;
  struct foo *p;
  p = &bar;
  p->a = 10;
  proof(&p);
  return (0);
}

however I get this error when I try and compile .. error: expected ‘;’, ‘,’ or ‘)’ before ‘*’ token
any help appreciated thanks al.

It's not

Code:

struct foo bar *p

it's

Code:

struct foo *p

This

Code:

struct foo{
    int a;
  }bar;

creates an instance of struct foo called bar.

A compiler starts at the top of the file and goes to the bottom.

Where you define your proof function, how does the compiler know about struct foo, when you've declared and defined it within main?

if you copied this from a textbook, naughty textbook.
if you wrote this yourself, naughty you

using foo, bar, p as variable names when you are trying to learn something just adds a layer of complexity that doesnt need to be there. ive rewritten the example so that it makes sense.

i changed 2 things. firstly where you define the struct. now, when i was taught about structures, we would always define them before main. so ive made that change. if you define a structure inside of main, then the structure definition would be local to the main function (that is, no one else but main can see the struct) which is why you get an error on your proof function. proof doesnt know what a 'struct foo' is. you have to define structures before you can write functions which use them.

the second thing is your line 'proof(&p)'. what this does is it passes the address of the variable p and gives it to the function. what we actually want is the address of bar, which is already stored in p. so the correct line is just 'proof(p);' without ampersand.

here is the code with my changes.

Code:

#include <stdio.h>

struct animal {
   char *name;
   int  legs;
};

void goToTheVet(struct animal* sickPet) {
   printf("hello %s. your %i legs are all healthy\n",
   sickPet->name, sickPet->legs);
}

int main(int argc, char* argv[]){

   struct animal myCat;

   struct animal *pointerToAnimal;
   pointerToAnimal = &myCat;

   pointerToAnimal->name = "Mr. Snuggles";
   pointerToAnimal->legs = 4;

   goToTheVet(pointerToAnimal);
   // this works too
   // goToTheVet(&myCat);
   return (0);
}

thanks for the help .. very much appreciated ..

my daughter has used my c programming book as a coloring in book and my wife has disappered it while I was at work ..