CODEWITHSUNDEEP
coperating-systemubuntu-16.04scheduling
Rajesh Gupta
Rajesh Gupta

Reputation: 21

Why is my programme showing Segmentation Fault on Ubuntu but working fine on Geeks IDE?

Experts, this is the program I made for First Come First Serve Scheduling in C language.
For the inputs like -
4
0 0 0 0
1 2 3 4

and inputs like -
5
0 1 2 3 4
4 3 1 2 5

My program is giving Segmentation fault (Core dumped) when I tried running it on my Ubuntu but it worked fine on GeeksForGeeks IDE.
And for the inputs like -
6
4 3 2 1 2 3
4 3 2 3 4 5

My program is working fine on my Ubuntu as well as on GeeksForGeeks IDE.

#include<stdio.h>
void main(){
    int n,i;
    printf("\nEnter the number of jobs:\n");
    scanf("%d",&n);
    int at[n],bt[n],at_copy[n];
    printf("\nEnter the arrival time:\n");
    for(i=0;i<n;i++){
        scanf("%d",&at[i]);
        at_copy[i]=at[i];   
    }    
    printf("\nEnter the burst time:\n");
    for(i=0;i<n;i++)
        scanf("%d",&bt[i]);
    int priority[n],min=at_copy[0],k,j;
    for(j=0;j<n;j++){
        min=at_copy[0];
        for(i=0;i<n;i++){
            if(at_copy[i]<min){
                min=at_copy[i];
                k=i;
            }
        }
        at_copy[k]=999;
        priority[j]=k;
    }
    int ct[n],wt[n],tat[n],t=0;
    for(i=0;i<n;i++){
        if(at[i]<t)
            k=0;
        else
            k=at[i];
        t+=bt[i]+k;
        ct[i]=t;
        tat[i]=ct[i]-at[i];
        wt[i]=tat[i]-bt[i];
    }
    printf("\nProcess\tAT\tBT\tCT\tTAT\tWT\n");
    for(i=0;i<n;i++){
       printf("P%d\t%d\t%d\t%d\t%d\t%d\n",i+1,at[i],bt[i],ct[i],tat[i],wt[i]);
    }
}

In the output, I am expecting a table like structure displaying the arrival time, burst time, completion time, burst time, turnaround time and waiting time of all the processes.

Upvotes: 1

Views: 69

Answers (1)

Ctx
Ctx

Reputation: 18420

Here:

int priority[n],min=at_copy[0],k,j;
for(j=0;j<n;j++){
    min=at_copy[0];
    for(i=0;i<n;i++){
        if(at_copy[i]<min){
            min=at_copy[i];
            k=i;
        }
    }
    at_copy[k]=999;
    ...

Imagine what happens, when at_copy[0] is the minimal value. Then, the condition atcopy[i]<min is never true and k remains uninitialized resulting in an out-of-bounds access here:

    at_copy[k]=999;

You have to initialize k with 0, since you assume in the first iteration, that at_copy[0] is the minimum.

int priority[n],min=at_copy[0],k=0,j;

With Geeks-IDE, you might have been "lucky" and k had the value 0 without being initialized.

Upvotes: 2

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