Thread: freopen....

I had a program which accepted input file on the command line and redirected output to file specified in the command line. So it was essentially

Code:

$ ./name_of_program <input_file >output_file

Code:

void  main(int Argc, char *Argv[])
/*    ----  */
{
    // Initialise the variables

    /*  Process options  */

    while ( (o = getopt(Argc, Argv, "nNus:a:f:g:V:d:A:w:l:t:m:v:")) != EOF )
    {
	if ( FirstTime )
	{
	    printf("\n    Options:\n");
	    FirstTime = false;
	}

	switch (o)
	{
	    case 'n': // Do some calculations
                       break;

	    case 'N': //Do some calculations
			break;
         }
       }

Now I made some modifications to this program to get it working with Java Native Interface. Also I used freopen to redirect stdin and stdout to the files. One other change that I made was that my program made use of getopt() function to parse the command line arguments. Since now I am not running it on the command line I put the calculations that were being done before the getopt() part. So my modified code looks like this.

Code:

void enter() {

    freopen("inputfile","r", stdin);
    freopen("outputfile","w", stdout);
    enter();
    fclose(stdin);
    fclose(stdout);
    
    // Run again with a different input and output file
    freopen("inputfile","r", stdin);
    freopen("outputfile","w", stdout);
    enter();
    fclose(stdin);
    fclose(stdout);

}

void  main()
/*    ----  */
{
    // Initialise the variables

   // Do some calculations
   // Do some calculations
    /*  Process options  */

    while ( (o = getopt(Argc, Argv, "nNus:a:f:g:V:d:A:w:l:t:m:v:")) != EOF )
    {
	if ( FirstTime )
	{
	    printf("\n    Options:\n");
	    FirstTime = false;
	}

	switch (o)
	{
	    case 'n': // Do some calculations
                       break;

	    case 'N': //Do some calculations
			break;
         }
       }

I got my executable and ran the program with just one input and output file and it ran smoothly. But when I ran it with two input and output files it crashes giving me a Segmentation Fault. If i put printf after I dont see the output being redirected to my output file.

Code:

    // Run again with a different input and output file
    freopen("inputfile","r", stdin);
    freopen("outputfile","w", stdout);
    printf("\nI am here");

Any clues on if there is an issue with using freopen multiple times.

Originally Posted by Bayint Naung

The original stream (if it exists) is closed.

Okay If I understand then I should be doing probably this.

Code:

int main(){
	
	freopen("err.txt","w", stderr);
	FILE* input = freopen("member.d", "r", stdin);
	FILE* output = freopen("log.txt", "w", stdout);
	enter();
	fflush(input);
	fflush(output);
	fclose(input);
	fclose(output);
	
	FILE* in = freopen("member.d", "r", input);
	FILE* out = freopen("log1.txt", "w", output);
	printf("\nI am here");
	enter();
	fflush(in);
	fflush(out);
	fclose(in);
	fclose(out);

	return 0;
}

void  enter()
/*    ----  */
{
    int		o, i, Cases, Errors;
    extern char	*optarg;
    extern int	optind;
    Boolean	FirstTime=true;
    Var		V;
    extern Var	*Arg;	/* in literal.c */
    Relation	R;
    Tuple	Case;
    char	Line[200], PlusOrMinus;

    /* Check overlaying of Const and float */

The good thing is that now I don't get "Segmentation Fault". But my second call to enter() is not generating the output that is genenrated in the first call.