no match for 'operator*' in 'shared_data *shm' error - c++

Question

This program is suppose to create a shared memory between a child and parent process where the child process saves into it the fibonacci sequence of a certain length (argument) and the parent process spits it out. it's also suppose to attach and detach the shared memory. Everything seems functional except for the fact that I get this error:
proj2.cpp:40: error: no match for 'operator*' in 'shared_data *shm' error
Any help? code below.
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <iostream>
#define MAX_SEQUENCE 10
struct shared_data{
long fib_sequence[MAX_SEQUENCE];
int sequence_size;
} shared_data;
using namespace std;
char * shm;
int Fibonacci(int n){
int first = 0, second = 1, temp = 0;
shared_data.fib_sequence[0] = first;
shared_data.fib_sequence[1] = second;
for(int i = 2; i<=n; i++){
temp = first + second;
shared_data.fib_sequence[i] = temp;
first = second;
second = temp;
}
return 0;
}
int main(int argc, char *argv[])
{
pid_t pid;
int seg_id;
const int shd = 4096;
seg_id = shmget(IPC_PRIVATE, shd, S_IRUSR | S_IWUSR);
shared_data *shm = shmat(seg_id, NULL, 0);
int number = atoi(argv[1]);
if(number < 0 || number > 10){
cout << "Invalid number. Please enter a number greater than 0 \n";
return(1);
}
shared_data.sequence_size = number;
pid = fork();
if(pid == 0)
Fibonacci(number);
else{
waitpid(pid,0,0);
for (int i = 0; i <= shared_data.sequence_size; i++)
cout << shared_data.fib_sequence[i];
cout << "\n";
}
return 0;
}

Answer 1

You defined a struct shared_data and at the same time created an object of type shared_data with the name .... shared_data.
Then you create a char* called shm.
So in shared_data *shm = shmat(seg_id, NULL, 0);, the * is interpreted as the binary * operator, trying to 'multiply' your object shared_data with your char pointer shm.

Answer 2

This line:
shared_data *shm = shmat(seg_id, NULL, 0);
has the following properties:
shared_data is an object, not a type.
shm is an object that was declared earlier as well.
You are attempting to multiply those two variables together, and then assign to the result.
You might want something like:
struct shared_data *shm = shmat(seg_id, NULL, 0);
Or you might want to use a typedef in your declaration of the shared_data struct.