Question

In the following program I try to pass a structure to a function. But I get errors,and I do not understand why. What mistake have I made in this program ?

I am using gcc for compiling this c program.

#include <stdio.h>

struct tester {
  int x;
  int *ptr;
};

void function(tester t);

int main() {
 tester t;
 t.x = 10;
 t.ptr = & t.x;
 function(t);
}

void function(tester t) {
   printf("%d\n%p\n",t.x,t.ptr);
}

---

Errors :

gcc tester.c -o tester

tester.c:8:15: error: unknown type name ‘tester’
tester.c: In function ‘main’:
tester.c:12:2: error: unknown type name ‘tester’
tester.c:13:3: error: request for member ‘x’ in something not a structure or union
tester.c:14:3: error: request for member ‘ptr’ in something not a structure or union
tester.c:14:13: error: request for member ‘x’ in something not a structure or union
tester.c: At top level:
tester.c:18:15: error: unknown type name ‘tester’

NOTE : If I replace printf with cout and stdio with iostream and name the extension to .cpp (!), I get no errors. Why is that ? No wonder I compile it using g++

Answer 1

If you don’t typedef the struct you must specify struct in front of the struct name while declaring it like so:

struct tester t;

Either you do that or you do the following:

typedef struct {
  int x;
  int *ptr;
}tester;

Update

Below is a quote from Adam Rosenfield from the following post Difference between ‘struct’ and ‘typedef struct’ in C++?:

In C++, all struct/union/enum/class declarations act like they are implicitly typedef’ed, as long as the name is not hidden by another declaration with the same name.