.. _readline:

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 :ref:`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.

* :download:`readfile.c`