Q39216: Opening Files Using Command Line Arguments.

Article: Q39216
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | s_quickc | mspl13_c
Last Modified: 29-DEC-1988

File names may be specified as command line arguments to a C
program.  The example below uses the first command line argument as
the name of the input file and the second as the name of the output
file.  The parameter argv, which is declared by main(), is used to
access the command line arguments.

In the example below, the following occurs:

1. argv[0] will contain a full path to the source (exe) file

2. argv[1] will contain the first argument, which is the input file
name

3. argv[2] will contain the second argument, which is the output file
name

The following program opens a file for reading and writing and
also prints argv[0], argv[1], and argv[2].  Note that argc is checked
to make sure that two argument strings were actually passed and that
the file pointers are checked to make sure that the files were
actually opened.

#include <stdio.h>

main (argc,argv)
int argc;
char *argv[];
{
  FILE *in, *out;

  if (argc < 3)  {         /* enough arguments? */
    puts("Usage:  demo infile outfile");
    exit(1);
  }

  printf("%s\n", argv[0]);
  printf("%s\n", argv[1]);
  printf("%s\n", argv[2]);

  in  = fopen (argv[1],"r");
  out = fopen (argv[2],"w");

  if (in == NULL || out == NULL)  {
    puts("Could not open both files");
    exit(2);
  }
  puts("Opened both files OK");
  exit(0);
}

The command line: "C:\>demo infile outfile" produces the
following output if infile and outfile can be opened:

   C:\demo.exe
   infile
   outfile
   Opened both files OK

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