Reading from input file for C

[ahteck5]

i am required to code in C but i have limited knowledge.
Can i read a certain number of lines in a input file, then stop reading and do some functions, then continue to read from the point where i stop by calling a method to read again?

[RedSon]

i am required to code in C but i have limited knowledge.
Can i read a certain number of lines in a input file, then stop reading and do some functions, then continue to read from the point where i stop by calling a method to read again?

Yes. Your input stream or input buffer will remember where it is as long as you have set up a pointer to the data.

[ahteck5]

Yes. Your input stream or input buffer will remember where it is as long as you have set up a pointer to the data.

How do i actually do it? At the moment, i only know how to read the first line from the input file

#include <stdio.h>
 
int main()
{
  int input_character;
  FILE *my_stream;
  char my_filename[] = "command.txt";
  // char my_string[100];
   int bytes_read;
  int nbytes = 100;
  char *my_string;
 
  my_stream = fopen (my_filename, "r");
 
  my_string = (char *) malloc (nbytes + 1);
  bytes_read = getline (&my_string, &nbytes,my_stream);
 
  /* Close stream; skip error-checking for brevity of example */
  fclose (my_stream);
 
  printf ("%s", my_string);
 
  return 0;
 
}
 

[RedSon]

How do i actually do it? At the moment, i only know how to read the first line from the input file

#include <stdio.h>
 
int main()
{
  int input_character;
  FILE *my_stream;
  char my_filename[] = "command.txt";
  // char my_string[100];
   int bytes_read;
  int nbytes = 100;
  char *my_string;
 
  my_stream = fopen (my_filename, "r");
 
  my_string = (char *) malloc (nbytes + 1);
  bytes_read = getline (&my_string, &nbytes,my_stream);
 
  /* Close stream; skip error-checking for brevity of example */
  fclose (my_stream);
 
  printf ("%s", my_string);
 
  return 0;
 
}
 

What if you put a loop around the getline statement? What if you didn't close the stream but instead did some functions then called getline again? There is nothing in the C language or steam class that says you have to read one line, then close the stream then do some functions with the data you read.

[ahteck5]

What if you put a loop around the getline statement? What if you didn't close the stream but instead did some functions then called getline again? There is nothing in the C language or steam class that says you have to read one line, then close the stream then do some functions with the data you read.

Thanks for the reply.

1) if my file contains multiple lines, how do i loop and print out each line until the end of file. I tried using read (bytes_read!=-1), but it gives me error.

2) I do not want to put a while loop bcos the function that will be running will invoke the readFile only when necessary..
Something like function A want to read 3 lines, then do it processing, then it want to read 4 lines.

Thks again

[RedSon]

Thanks for the reply.

1) if my file contains multiple lines, how do i loop and print out each line until the end of file. I tried using read (bytes_read!=-1), but it gives me error.

2) I do not want to put a while loop bcos the function that will be running will invoke the readFile only when necessary..
Something like function A want to read 3 lines, then do it processing, then it want to read 4 lines.

Thks again

1) There must be a way to tell if the stream has more data in it to read or if it has reached the end of file. You will have to read up on the documentation of the stream code or getline to see what the end of file result is.

2) Then put the readFile inside an if statement and then if a certain condition is met then you can read the file again.