dereferencing pointer to incomplete type

[johnny_]

how can i fix the following? i get "dereferencing pointer to incomplete type" on compilation inside the func()

#include <stdio.h>

void func(char *buf) {
	printf("x func: %d\n", (*(struct s1 *)buf).x);
}


int main() {
	struct s { int x; };

	struct s s1;
	s1.x = 5;
	printf("x main: %d\n", s1.x);
	func((char *)&s1);	

	return 0;
}

[sganesh]

You can convert directly that character pointer into integer,.

void func(char *buf) {
        printf("x func: %d\n", *((int *)buf));
}

[johnny_]

but you didn't refer to the int value inside the struct.
it's just a portion of something i would like to achieve.
here is another example.

file: tester.c

#include <stdio.h>
#include <string.h>
//#include "z.h"
#include "/usr/include/netinet/ip.h"

void func(struct ip *ip) {
	printf("ip_ttl func: %d\n", (*(struct ip *)ip).ip_ttl);
}

int main() {

	struct ip tmp;
	memset(&tmp, 0, sizeof(struct ip));
	tmp.ip_ttl = 0x4;

	char buf[sizeof(struct ip)];
	memset(buf, 0, sizeof(struct ip));
	memcpy(buf, &tmp, sizeof(struct ip));

	printf("ip_ttl main: %d\n", tmp.ip_ttl);
	printf("ip_ttl main: %d\n", (*(struct ip *)buf).ip_ttl);

	func((struct ip *)&tmp);
	func((struct ip *)buf);

	return 0;
}

and the output for it:
# ./tester
ip_ttl main: 4
ip_ttl main: 4
ip_ttl func: 4
ip_ttl func: 4

now modifying it to:
file: tester.c

#include <stdio.h>
#include <string.h>
#include "z.h"
/*#include "/usr/include/netinet/ip.h"

void func(struct ip *ip) {
	printf("ip_ttl func: %d\n", (*(struct ip *)ip).ip_ttl);
}*/

int main() {

	struct ip tmp;
	memset(&tmp, 0, sizeof(struct ip));
	tmp.ip_ttl = 0x4;

	char buf[sizeof(struct ip)];
	memset(buf, 0, sizeof(struct ip));
	memcpy(buf, &tmp, sizeof(struct ip));

	printf("ip_ttl main: %d\n", tmp.ip_ttl);
	printf("ip_ttl main: %d\n", (*(struct ip *)buf).ip_ttl);

	func((struct ip *)&tmp);
	func((struct ip *)buf);

	return 0;
}

file: z.h

#ifndef Z_H
#define Z_H

#include "/usr/include/netinet/ip.h"

void func(struct ip *ip);

#endif

file: z.c

#ifndef Z_C
#define Z_C

#include "z.h"
#include <stdio.h>

void func(struct ip *ip) {
	printf("ip_ttl func: %d\n", (*(struct ip *)ip).ip_ttl);
}

#endif

the output now is the same as above.
but, when i try to do the same thing around other program of mine. it gives me the "dereferencing pointer to incomplete type".

SHOULD I PAST MY ORIGINAL CODE?
WILL SOMEONE BE ABLE TO HELP?

[Alexander jack]

If you want to get using struct
then try this

 printf("x func: %d\n",*(struct s *)buf);

This will work when the structure has only one member ,

since we are dealing with the reference we must use this one,

        printf("x func: %d\n",((struct s *)buf)->x);

The main issue is if you want to dereference in the function you must be defining the structure outside the main
function , since you are actually facing a scope related issues.

[Salem]

> You can convert directly that character pointer into integer,.
Look up what an "alignment exception" is some time, otherwise known as a bus error.

> it gives me the "dereferencing pointer to incomplete type".
So include some header file that declares struct s1