READING CSV USING SYSTEM CALLS

Demonstration to read csv using fgets and then calculate average of the scores of section A and section B using fork().

Steps to run

#Makefile
all: q1 q1.o
q1:q1.o
	gcc q1.o -o q1
	./q1

q1.o:q1.c
	gcc -c q1.c -o q1.o
	gcc -S q1.c -o q1.s
	gcc -E q1.c -o q1.i

As the main function is evoked we create a process using fork().
Parent function reads the csv file ,computes the average of each student in section B.
Child process does the same thing but for section A students.I used a struct called student to store roll no,section,scores in 4 assignments and its average.
Made an array of struct students and computed average differently for both processes.


typedef struct student{
   int rollno;
   char section[1];
   int marks1;
   int marks2;
   int marks3;
   int marks4;
   float avg;

}stud;

Removed the storage of the first line i.e label so that the values are stored accordingly.

While forking the current process -checked whether fork is being done properly or not(pid<0)

 if (pid < 0) {
      perror("fork() failure\n");
      return 1;
   }

In the child process ,after all the tasks are done I used exit(0) to avoid abrupt ending and signalling the parent process about the exit.
In the parent process,I used the waitpid() command to wait till the child process exited then checked it using WIFEXITED(status) command. waitpid(pid,&status,0); if(WIFEXITED(status))

While using read syscall -i required file descriptor,buff to store ,and its size to be mentioned so that it can read that amount of bytes from the file.
But when i used it i couldn't get the correct amount of size to be sent to the buffer since each line has different no of bytes requirement as in some columns roll no was 3 digit and marks in 1 digit.
So if i read some amount of bytes for the first line if the second line required one more or less bytes got affected in the second run of loop so i couldn't extract the line and its values.Thus,incorrect values get stored into the specific fields of the struct thereby giving wrong output.

  read(fd,buff,1024);
  printf("%s",buff );
  write(1,buff,1024)

Fgets-requires pointer to that file ,size of the input line and the pointer to store input line. while(fgets(temp[i],1024,fd))
Once the line is stored in the array,I used string_token strtok() to break it into parts and store it in the respective fields of the struct(here student).
Usually open int fd= open("data.csv",O_RDONLY)is used to get file descriptor since I used fgets(), I used fopen to get file pointer.Both take similar arguments name of the file and mode of the file to be opened asFILE *fd= fopen("data.csv","r")
I used the printf function to print the values to the console .

The input file must contain the first line as a label(student id,section,scores etc).
The input file must have only these entries and in the same order as roll no,section,marks1,marks2,marks3,marks4.
The input file is a space separated csv file named as data.csv.