6.7. String Example - ReadLine

Let us now consider an example of string processing along with file I/O. This program simply reads a file and displays its contents. It uses a function called ReadLine that provides a more robust mechanism for reading lines of text than scanf(). The name of the file to read is passed as a command line argument.

#include <stdio.h>
#include <string.h>

#define MAXLINE 150
#define true 1
#define false 0
int ReadLine(char *,int ,FILE *);

int main(int argc, char **argv)
{
  char line[MAXLINE];
  FILE *fp;

  if(argc < 2) {
      printf("USAGE: %s filename\n", *argv);
      printf("list a file name on the command line to be read and printed\n");
      return 1;
      // In Unix: exit(1);
  }
  if ((fp = fopen(argv[1], "r")) == NULL) {
      printf("cannot open file %s\n", argv[1] );
      return 1;
  }

  /*
   * Use ReadLine to read the whole file - just print it out for
   * this example.
   */
  while( ReadLine(line, MAXLINE, fp) ) {
      printf( "%s\n", line );
  }
  /*
   * remember to close the file.
   */
  fclose(fp);
  return 0;
}


int ReadLine(char *buff, int size, FILE *fp)
{
  buff[0] = '\0';
  buff[size - 1] = '\0';             /* mark end of buffer */
  char *tmp;

  if (fgets(buff, size, fp) == NULL) {
      *buff = '\0';                   /* EOF */
      return false;
  }
  else {
      /* remove newline */
      if ((tmp = strrchr(buff, '\n')) != NULL) {
        *tmp = '\0';
      }
  }
  return true;
}

Here is this file that may be downloaded.

• readfile.c