Hi all. I am new to C, at least to the concept of pointers. I am trying to write a process scheduling simulator for my operating systems class (at the last minute of course). Anyway, I wrote a program just using arrays and got it to compile but then of course I got a Segmentation Fault so I am trying to start fresh using pointers. Right now, all I want to do is take the input file and add the pieces of input into structs (this part works) but then when I add a for loop to go through the structs again and increment values, etc. I get another segmentation fault. Here is the code:

#include <stdio.h>
#include <stdlib.h>

int p, clock;
int addition, numJobs;
int i, j, availableMem;

// Enum, structure declarations
enum state {
        NOTARRIVED,
        NOTINSYSTEM, 
        READYTORUN,
        SLEEPINGIO,
        RUNNING,
        EXITED
} currentState;

/*******************************************************
For each process:
unique PID, arrival time, service time, priority rating,
memory allocation, no start, time in IO state,
time in Ready to Run state, time in Running state,
timeslice
*******************************************************/
typedef struct
{
    int pid;
    int arrivalTime;
    int serviceTime;
    int priorityRating;
    int memoryAllocation;
    int noStart;
    int timeInIO;
    int timeInReadytoRun;
    int timeslice;
    int memTaken;
    enum state currentState;
} process;

typedef struct
{
    process elems[1000];
    int back; // Initialized to -1
    int front; // Initialized to 0
} queue;

/* Input processes from data file into array of structs:
    Process ID : Arrival Time : Service Time : Priority : Memory Requirement in MB */
process *proc[20];

/* Priority Queues: 0, 1, 2, 3, 4, I/O queue, Not In System queue. */        
queue queue0, queue1, queue2, queue3, queue4, queueIO, queueNoMem;    

/* Begin Main */
int main(int argc, char *argv[0])
{
    char  line[80];
    FILE *inputFile, *outputFile;
    
    inputFile = fopen("input_file.txt", "r");

    if (inputFile == NULL) 
    {
        fprintf(stderr, "Can't open input file!\n");
        exit(1);
    }

    outputFile = fopen("output_file.txt", "w");

    if (outputFile == NULL) 
    {
        fprintf(stderr, "Can't open output file!\n");
        exit(1);
    }
    
    p = 0;
    clock = 0;
        
    fprintf(outputFile, "Input File: \n");

    while(fgets(line, 80, inputFile))
    {
        int uniquePID, arriveTime, serviceTime, priority, memAlloc;

        sscanf(line, "%d : %d : %d : %d : %d", &uniquePID, &arriveTime, &serviceTime, &priority, &memAlloc);    

        proc[p] = (process *)malloc(sizeof(process));

        proc[p]->pid = uniquePID;
        proc[p]->arrivalTime = arriveTime;
        proc[p]->serviceTime = serviceTime;
        proc[p]->priorityRating = priority;
        proc[p]->memoryAllocation = memAlloc;
        proc[p]->noStart = 0;
        proc[p]->timeInIO = 0;
        proc[p]->timeInReadytoRun = 0;
        proc[p]->timeslice = 0;
        proc[p]->currentState = NOTARRIVED;

        // LATER -> free(proc[p]);
        
        addition = proc[p]->memoryAllocation%4;
        proc[p]->memTaken = proc[p]->memoryAllocation + addition;

        fprintf(outputFile, "PID = %d Arrival Time = %d Service Time = %d Priority = %d Memory Needed = %d \n", 
                  proc[p]->pid, proc[p]->arrivalTime, proc[p]->serviceTime, proc[p]->priorityRating, proc[p]->memoryAllocation);

        p++;
    }

    // Set total number of jobs
    numJobs = p;

    fprintf(outputFile, "Number of jobs: %d \n", numJobs);

    // Set memory size for entire simulation
    availableMem = 32;

    fprintf(outputFile, "Available Memory: %d \n", availableMem);

    // THIS IS WHERE I THINK THE SEGMENTATION FAULT OCCURS
    // WHEN I TRY TO ACCESS THE PIECES IN THE STRUCTS
    // Add new incoming jobs to the "Ready to Run" state
    for(i = 1; i <= numJobs; i++)
    {
         if(availableMem > proc[i]->memTaken)
            {
                // Allocate necessary memory for this process
                availableMem = availableMem - proc[i]->memTaken; 

                // Set the state to Ready to Run
                proc[i]->currentState = READYTORUN;
            }
            else
            {
               // Keep this job out of the system until 
               // more memory is available
                proc[i]->currentState = NOTINSYSTEM;
                proc[i]->noStart++;
            }
    }
}

Any advice, tips would be greatly appreciated! Thanks so much!

int main(int argc, char *argv[0])

That looks strange.

You're right, I got that from a really old simple program. Although, I don't think that is the reason for the problem because I do get the data from the input file. I just do not have the right syntax - or idea - about how to loop through the structs and increment values in them.

Thank you for the quick reply!

int main(int argc, char *argv[0])

That looks strange.

Yes, it should be

int main(int argc, char *argv[])

I tried running the same code but didnt got any segmentation fault.
Just changed the prototype of main and try it

Sorry Knorden ... Me too got it

Solution is simple.....

Instead of using for(i = 1; i < = numJobs; i++) use
for(i = 1; i < numJobs; i++)

The array was going out of bound.

Sorry Knorden ... Me too got it

Solution is simple.....

Instead of using for(i = 1; i < = numJobs; i++) use
for(i = 1; i < numJobs; i++)

The array was going out of bound.

Wow I definitely should've caught onto that. Thanks!

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