Writting on a file

im working on a project for college and I have a problem. I have to manage a theatre room. Everything is fine about it, but now I have to copy the state of the room to a file. When I call the function guarda_estado_sala(), which should print the ids of the clients in the file (stored at the variable sala which is a pointer), it doesn't do anything at all. I even added a printf inside the function, but it doesn't work, any clues on why?

Here is the code (the function I need to change is marked with a comment):

//Cuerpo biblioteca
#include <stdlib.h> 
#include <stdio.h>
//cabeceras archivos
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h> //para close
int* sala;
int aforo;
void crea_sala(int capacidad){
sala = (int*) malloc(capacidad* sizeof(int));
aforo = capacidad;
for(int i = 0; i<capacidad; i++){
*(sala+i) = -1;
}
}
int reserva_asiento(int id){
for(int i = 1; i <= aforo; i++){
if(*(sala+i-1) ==id){
return -2;
}
}
for(int i = 1; i <= aforo; i++){
if(*(sala+i-1) ==-1){
*(sala+i-1) = id;
return i;
}
}
return -1;
}
int libera_asiento(int asiento){
int devuelve = *(sala+asiento-1);
*(sala+asiento-1) = -1;
return devuelve;
}
int estado_asiento(int asiento){
if(*(sala+asiento-1) == -1){
return 0;
}else if(*(sala+asiento-1) > 0){
return *(sala+asiento-1);
}else{
return -1;
}
}
int asientos_libres(){
int contador = 0;
for(int i = 1; i<=aforo; i++){
if(estado_asiento(i) == 0){
contador++;
}
}
return contador;
}
int asientos_ocupados(){
return aforo-asientos_libres();
}
int capacidad(){
return aforo;
}
void elimina_sala(){
free(sala);
}
int encuentra_asiento(int id){
for(int i = 0; i<aforo; i++){
if(estado_asiento(i) == id){
return i+1;
}
}
return -1;
}
// THIS IS THE FUNCTION:
int guarda_estado_sala(const char* ruta_fichero){
int fd = creat(ruta_fichero, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
for(int i=0; i<aforo; i++){
write(fd, (char) *(sala+i), sizeof(char)); 
}
close(fd);
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include "../cabeceras/sala.h"
void main(){
crea_sala(10);
reserva_asiento(10);
guarda_estado_sala("saladeprueba.txt");
elimina_sala();
}

This is wrong in multiple ways:

write(fd, (char) *(sala+i), sizeof(char)); 

• (char) *(sala+i) This dereferences sala[i] and cast it to a char. You should supply a void*.
• sizeof(char) is not the correct size since you are writing ints. Corrected, it'd look like this:

for(int i = 0; i < aforo; i++) {
    write(fd, sala + i, sizeof *sala);
}

but, there's no reason to do it in a loop. Just write it all at once:

write(fd, sala, aforo * sizeof *sala);