I've looked over this about 15 times by now to no avail. I cannot understand why this is seg faulting? It doesn't even get to the "print" statement which makes no sense. the error codes actually do work tho (when I dont have a shared memory present) I have a load.c program but it works perfectly (im 100% sure of this)
#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <sys/sem.h>
#include "header.h"
//BEGIN MAIN FUNCTION
main()
{
int id; //ID to data shmem
struct StudentInfo *infoptr; //ptr to data
int found = 0; //found 'boolean'
char input[15]; //user input buffer
struct StudentInfo *beginptr; //ptr to beginning of data
int rcid; //Read count ID to shmem
int *rcptr; //RC ptr
int sema_set; //ID to shared semaphores
//Find the shmem at our ID
id = shmget(KEY,SEGSIZE,0);
if(id < 0)
{
perror("Query: shmget failed");
exit(1);
}
//set the ptr to our shared mem and attach to program
infoptr = (struct StudentInfo *)shmat(id,0,0);
if(infoptr <= (struct StudentInfo *)(0))
{
perror("Query: shmat failed");
exit(1);
}
//Get our RC in shared memory
rcid = shmget(RCKEY,READCOUNT,0);
if(rcid < 0)
{
perror("Query: shmget failed");
exit(1);
}
//Set ptr to shmem and attach to process
rcptr = (int*)shmat(rcid,0,0);
if(rcptr <= (int*)(0))
{
perror("Print: Shmat failed");
exit(1);
}
//Get semaphores
sema_set = semget(SEMA_KEY,NUM_SEMAPHS,0);
if(sema_set < 0)
{
perror("Query: Semget failed");
exit(1);
}
//Set program to queue up to wait
Wait(sema_set,1);
//Increment the read counter
*rcptr += 1;
//If we are the first reader, stop writers
if(*rcptr == 1)
Wait(sema_set,0);
//Signal readers
Signal(sema_set,1);
//Set our begin ptr
beginptr = infoptr;
//Begin user input loop
while(1)
{
//Ask user for input IT DOESN"T EVEN GET TO HERE <--
printf("Please input a student ID :");
scanf("%s",input);
//While the record is not found search
while(strcmp(infoptr->Name,"")!=0 && found != 1)
{
//If record found, print the record
if((strncmp(input,infoptr->ID,9)) == 0)
{
//Set found
found = 1;
printf("\n%s\n",infoptr->Name);
printf("%s\n",infoptr->telNumber);
printf("%s\n",infoptr->Address);
printf("%s\n\n",infoptr->ID);
}
else
infoptr++;
}
//If not found, print error message
if(found == 0)
printf("Record not found.\n");
//Wait on readers
Wait(sema_set,1);
//Decrement
*rcptr--;
//If no readers left
if(*rcptr == 0)
Signal(sema_set,0); //Signal writers
//Signal readers
Signal(sema_set,1);
exit(0);
}
}
HEADER
#define KEY ((key_t)(11111)) /*change it to last five digits of your SSN*/
#define SEGSIZE sizeof(struct StudentInfo)
#define NUM_SEMAPHS 2
#define SEMA_KEY ((key_t)(1111)) /* change this to last four digits of SSN */
#define READCOUNT sizeof(int) //Set the size of shmem for read count
#define RCKEY ((key_t)(4003)) //Set the key of the shmem for RCount
//Struct student info
struct StudentInfo{
char Name[20];
char ID[15];
char Address[50];
char telNumber[15];
};
//Checks the semaphore whether or not to wait
void Wait(int semaph, int n);
//Signals that it's ok to run
void Signal(int semaph, int n);
//Gets the semaphore information
int GetSemaphs(key_t k, int n);