passing a structure pointer by value

hello all,
well I am getting really frustrated with something. I read on a post here that passing by value is supported in C, and that bassing by referance is only supported by C++. I am programming an program with a .CPP extension, but my application is using the C standard library and what I would consider at least 95% of C style code (I've yet to learn alot of C++).

anyways I also read here that passing structures by value can be beneficial over passing by reference with larger structures. I am just wondering how I can get the contents of the structure in my function. I keep trying different ways, and I keep getting errors. anyways here is what my code looks like:

Code:

---

typedef struct s {
  int i;
  char a;
} S, *PS;

void somefunc(PS);

int main(void)
{
  S var;
  PS pvar = &var;
  pvar->i = 10;
  pvar->a = 'b';

  somefunc(pvar);

  return 0;
}

void somefunc(PS ps)
{
  /* now, I would like to declare a local variable of s, but I don't
  know if I should use the S or PS type. I am assuming I should
  use a referance to assign the local variable the contents of ps,
  but I am also having problems with this. */
}

---

my structure is larger than that, that is just an example (if it was that small, I wouldn't bother passing by pointer). as you can see I am totally unsure of things locally in somefunc(), and like I said I have tried just about every possible way I can think of and keep getting errors. if someone could please show me how things should look in somefunc(), it would be GREATLY appreciated.

thank you very much in advance! :)

You can just use the ps pointer that somefunc() receives directly:

Code:

---

void somefunc(PS ps)
{
  printf("%d - %c\n", ps->i, ps->a);
}

---

The -> operator is the equivalent of doing (*ps).i or (*ps).a

> I read on a post here that passing by value is supported in C, and that bassing by referance is only supported by C++.
True.

> anyways I also read here that passing structures by value can be beneficial over passing by reference with larger structures.
That's the first time I heard something like that. It's not likely to be true, since a pointer to a struct is the size of the struct itself. It wouldn't save you much memory or time. In a previous thread I posted the way to mimic a reference in C, you might want to read that thread. http://cboard.cprogramming.com/showthread.php?t=80672
In a way you are still passing by value, but whereas one pointer can get to be very big, a pointer to a pointer is not.

Quote:

---

Originally Posted by citizen

since a pointer to a struct is the size of the struct itself.

---

A pointer to a struct is the size of a pointer.

Code:

---

itsme@itsme:~/C$ cat structexample.c
#include <stdio.h>

int main(void)
{
  struct foo { int i; char a; };

  struct foo bar;
  struct foo *whee;

  printf("sizeof bar: %u\n", sizeof(bar));
  printf("sizeof whee: %u\n", sizeof(whee));

  return 0;
}

---

Code:

---

itsme@itsme:~/C$ ./structexample
sizeof bar: 8
sizeof whee: 4
itsme@itsme:~/C$

---

>>I am programming an program with a .CPP extension<<

Generally, cpp files are treated as c++ source and compiled accordingly; similarly, 'c' source files are compiled as c. Unless your compiler is for 'c' only or you have supplied extra compiler switches, this will probably be compiled as c++ and not c.

thanks for your reply itsme86. I got it working fine now. :)

Code:

---

void somefunc(PS ps)
{
      S s = *ps;
}

---

The contents of *ps are copied by value into s