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error: invalid application of ‘sizeof’ to incomplete type ‘struct shared_use_st’

shmid = shmget(1294,sizeof(struct shared_use_st),0666 | IPC_CREAT);

struct shared_use_st *shared_stuff;

s1.c:51: error: ‘shared_use_st’ undeclared (first use in this function)
s1.c:51: error: (Each undeclared identifier is reported only once
s1.c:51: error: for each function it appears in.)

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/shm.h>

#include <sys/sem.h>

//#include "shm_com.h"





union semun

{ int val, arg1, arg2; /* hodnota pre SETVAL */

struct semid_ds *buf; /* buffer pre IPC_STAT, IPC_SET */

unsigned short int *array; /* pole pre GETALL, SETALL */

struct seminfo *__buf; /* buffer pre IPC_INFO */

};



static int set_semvalue(void);

static void del_semvalue(void);

static int semaphore_p(void);

static int semaphore_v(void);

static int sem_id;





int main()

{

 int i;

 int pause_time;

 char op_char = 'X';

 srand((unsigned int)getpid());

 int running = 1;

 void *shared_memory = (void *)0;

 struct shared_use_st *shared_stuff;

 int shmid;

 srand((unsigned int)getpid());

 



sem_id = semget((key_t)1284, 1, 0666 | IPC_CREAT);

if(sem_id==-1){

perror("semget()");

exit(EXIT_FAILURE);

}



printf("Program sem1.c ID semaforu: %d\n",sem_id);

if (!set_semvalue()) {

fprintf(stderr, "Failed to initialize semaphore\n");

exit(EXIT_FAILURE);

}



shmid = shmget(1294,sizeof( shared_use_st),0666 | IPC_CREAT);



if (shmid == -1) {

fprintf(stderr, "shmget failed\n");

exit(EXIT_FAILURE);

}





shared_memory = shmat(shmid, (void *)0, 0);

if (shared_memory == (void *)-1) {

fprintf(stderr, "shmat failed\n");

exit(EXIT_FAILURE);

}



printf("Memory attached at %X\n", (int)shared_memory);

shared_stuff = (struct shared_use_st *)shared_memory;



sleep(2);

while(running) {

     if (!semaphore_p()) exit(EXIT_FAILURE);

         printf("You wrote: %s\n", shared_stuff->some_text);

       if (!semaphore_v()) exit(EXIT_FAILURE);

              if (strncmp(shared_stuff->some_text, "end", 3) == 0) {

                  running = 0;

}

sleep(1);

}

del_semvalue();



if (shmdt(shared_memory) == -1) {

fprintf(stderr, "shmdt failed\n");

exit(EXIT_FAILURE);

}

if (shmctl(shmid, IPC_RMID, 0) == -1) {

fprintf(stderr, "shmctl(IPC_RMID) failed\n");

exit(EXIT_FAILURE);

}

exit(EXIT_SUCCESS);

}







static int set_semvalue(void){

union semun sem_union;

sem_union.val = 1;

if (semctl(sem_id, 0, SETVAL, sem_union) == -1) return(0);

return(1);

}



static void del_semvalue(void){

if (semctl(sem_id, 0, IPC_RMID) == -1)

fprintf(stderr, "Failed to delete semaphore\n");

}





static int semaphore_p(void)

{

struct sembuf sem_b;

sem_b.sem_num = 0;

sem_b.sem_op = -1;

sem_b.sem_flg = SEM_UNDO;

if (semop(sem_id, &sem_b, 1) == -1) {

fprintf(stderr, "semaphore_p failed\n");

return(0);

}

return(1);

}





static int semaphore_v(void)

{

struct sembuf sem_b;

sem_b.sem_num = 0;

sem_b.sem_op = 1;

sem_b.sem_flg = SEM_UNDO;

if (semop(sem_id, &sem_b, 1) == -1) {

fprintf(stderr, "semaphore v failed\n");

return(0);

}

return(1);

}