/********************************************************************
---------------------------------------------------------------------
MODUL  : $RCSfile: openfile.c,v $

TASK   : Opens a file. If the file name is not specified, the user
         will be asked for it. In case of a wrong user input it can
	    betried again until WDH times. A pointer to the opend file
	    will be returned. 

INPUT  : infostr - Short description of the file
         file    - file name
                 ( Attention! Length of file name is limited )
         mode    - Handling mode for the file (r , w)
         dialog  - Flag: 1 for interactive work, 0 otherwise

OUTPUT : Pointer to the opened file
         ( NULL at error )

GLOBAL : Possible failures will be stored in the global variable
	    errno.

AUTHOR : Dr. Vinzenz Brendler
         Research Center Rossendorf Inc., Institute of Radiochemistry

VERSION : $Revision: 1.1 $         $Date: 1996/09/17 07:56:58 $
---------------------------------------------------------------------
********************************************************************/

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

#define WDH		2		/* Number of user input retrials */
#define PROMPT1	"Name of"
#define PROMPT2	"?? Please try again for"

extern int errno;

FILE *openfile(infostr, file, mode, dialog)
	char infostr[];				/*  File descriptor  */
	char file[];					/*  File name        */
	char mode[];					/*  Access mode      */
	short int dialog;				/*  Interactive ?    */
{
	FILE *filepointer;

	char filename[BUFSIZ];

	if(strlen(file) < BUFSIZ)
		strcpy(filename, file);
	else
		return(NULL);

	if(dialog)
		dialog += WDH;

	if(dialog && !strlen(filename))  {
		fprintf(stderr, "%s %s : ", PROMPT1, infostr);
		if(gets(filename) == NULL)
			return(NULL);
	}

	do  {
		if(dialog)
			dialog--;
		errno = 0;
		if((filepointer = fopen(filename, mode)) == NULL)  {
			perror(filename);
			if(dialog)  {
				fprintf(stderr, "%s %s : ", PROMPT2, infostr);
				if(gets(filename) == NULL)
					return(NULL);
			}
		}
	} while(dialog && errno);

	return(filepointer);
}