Thread: some basic questions about pointers and structs...

i would like (if it is possible) someone to explain the program. i know that it is not a complete program but...i have the following questions...

(1) is this the same as

Code:

char name[];

?
if 'yes' what is the difference?

(2) is the following a correct way of calling the function from main()?

Code:

int main(void){
   init(*p);
}

if 'yes' what is the difference of this:

Code:

int main(void){
   init(p);
}

and lastly i want to know what -> is? can i have some more details about this please, cause i don' t understand...

Code:

#include <stdio.h>

struct Person{
   char *name; // (1)
   int age;
};

void init(struct Person *p){ // (2)
   p->name = (char *)malloc(10*sizeof(char));
   p->age = 0;
}

thank you all....

Pointers are a bit of a pain to explain if you ask me. To understand pointers you must realise what a variable in a computer program is - some data in memory. All a pointer is, is a variable which stores the memory address of a certain variable one of the advantages of this (among others) is improved computational performance when calling functions etc.

When you call a function and you pass a variable to that function it makes a copy of the variable and works on the copy, but if you pass a pointer into the function any operations are directly applied to the variable in question. It is easiest to see with a few examples so here we go:

Code:

int FuncOne(int val)
{
      return (2*val);
}

int FuncTwo(int * val)
{
      return (2*(*val));
}

/* First Main Example */
int main(int argc, char *argv[])
{
    int val = 5.0;
    int * val_ptr = &val;
    
    val = FuncOne(val);
    val = FuncTwo(val_ptr);
    
    val = FuncOne(*val_ptr);
    val = FuncTwo(&val);
    
    printf("%d\n", val);
    
  return 0;
}

FuncOne and FuncTwo do exactly the same thing but they do it differently. The '*' signifies a pointer and the '&' signifies the address of the variable. I know this isn't a very thorough explanation. Imagine a variable and a pointer as boxes and inside the pointer box there is the location of the variable box and inside the variable box is the value of the variable itself. The '*' and '&' are just ways of moving from one to the other.

The '->' operator is used to access variables defined through pointers, but I'll let someone else talk about those. I've got things to do right now.

thank you all guys...