What is the problem here

clunix · 04-10-2006, 09:36 AM

hi my friends
I have written this program
#include<stdio.h>
#include<unistd.h>
FILE*a;
main()
{
int z,status;
a=fopen("result.txt","r+");
if(fork()==0)
{
printf("I am the child\n");
z=2+5;
fprintf(a,"%d",z);
}
else
{
wait(&status);
printf("I am the perant,I will prent the result\n");
fscanf(a"%d",&z);
printf("%d",z);
}
}
*****************
And the result was
I am the child
I am the perant
1073824832
**************
I think should be :
*****************
I am the child
I am the perant
7
******************
What is this number 1073824832!!!!
please help me if you can

manishsingh4u · 04-10-2006, 09:44 AM

mann@Manish:~$ cc test.c -o test
test.c: In function ‘main’:
test.c:18: error: syntax error before string constant

PTrenholme · 04-10-2006, 10:02 AM

Your fprintf statement (the one manishsingh4u commented about) is printing the address of z, (i.e., &z), not the value of z. The number you display is reasonable for an address value.

perfect_circle · 04-10-2006, 10:24 AM

and please use the code tag. Your code is not readable.
Doesn't this look a lot better?

Code:

#include <stdio.h>
#include <unistd.h>

main()
{
	FILE*a;
	int z,status;
	a=fopen("result.txt","r+");
	if(!fork()){
		printf("I am the child\n");
		z=2+5;
		fprintf(a,"%d",z);
	}
	else{
		wait(&status);
		printf("I am the parant,I will prent the result\n");
		fscanf(a,"%d",&z);
		printf("%d",z);
	}
}

addy86 · 04-10-2006, 12:37 PM

You made a very bad mistake: you didn't check the return value of fopen. On my system the program even segfaults (for some reason, fscanf doesn't seem to check for NULL-pointers).
fopen( ..., "r+" ) opens for reading and writing, but it doesn't create the file, and thus fails. If the file already exists, it works.

clunix · 04-10-2006, 01:06 PM

hi my friends
thnak you for replay
DO not worry about syntax errors my main problem is
I don't want to prnit the adderss of z I want the perant to print value of 7
that is WHAT I WANT ,,
thank you again for replying...

addy86 · 04-10-2006, 01:16 PM

I can't help you if you don't read my posts. It is not printing the address of z,
printf("%d",z);
is correct and will print 7. As I already wrote, the bug is in the fopen function call of and the lack of checking the return value of fopen.

clunix · 04-11-2006, 12:49 AM

thank you mr.add86
Let's us forget writing and reading from file
I will write program without files

#include<stdio.h>
#include<unistd.h>
main()
{
int status,z;

if(fork()==0)
{
printf("I am the child\n");
z=2+5;
}
else
{
wait(&status);
printf("I am the perant\n");
printf("Z=%d",z);
}
}

here it will not printf 7
it will print something like address

paulsm4 · 04-11-2006, 01:16 AM

Uh - Z remains uninitialized in the parent.

You realize, of course, that just because a child shares a *copy* of the parent's data ... it doesn't share the data itself. The process space of a parent and a child are completely seperate.

clunix · 04-11-2006, 01:24 AM

ok my friend"paulsm4",,,,
How can I solve this problem????????????

paulsm4 · 04-11-2006, 01:38 AM

Code:

#include<stdio.h>
#include<unistd.h>

int
main()
{
  int status = 0, z = 8;

  // the child will print "7"...
  if(fork()==0)
  {
    z=2+5;
    printf("I am the child, z= %d\n", z);
  }
  // ... the parent will print "8"
  else
  {
    wait(&status);
    printf("I am the parent, z= %d\n", z);
  }

  //  ... and neither should print uninitialized garbage any more...
  return 0;
}

Here's another version of your original program:

Code:

#include<stdio.h>
#include<unistd.h>

int
main()
{
  FILE *fp = NULL;
  int z = 0, status = 0;

  // Fork the process
  if(fork()==0)
  {
    // .. Child: write the value to a text file
    z = 2 + 5;
    printf("I am the child, z = %d\n", z);
    if (fp = fopen ("result.txt", "w"))
    {
      fprintf (fp, "%d",z);
      fclose (fp);
    }
  }
  else
  {
    // .. Parent: wait until the child completes, then read the value from the file
    wait (&status);
    printf ("I am the parent, I will print the result...\n");
    if (fp = fopen ("result.txt", "r"))
    {
      fscanf (fp, "%d", &z);
      fclose (fp);
      printf("z= %d", z);
    }
  }

  return 0;
}

manishsingh4u · 05-13-2006, 03:18 PM

I have a very simple program which is not running fine as expected. I know there's some mistake from my side but where?

Code:

#include<stdio.h>
struct s
{
	char name[20];
	int age;
	int fare;
	char gender;
}s[3];
int main()
{
	int i,sum=0;
	for(i=0;i<3;i++)
	{
		printf("\nenter the name of passenger ");
			scanf("%s",s[i].name);
		printf("\nenter the age of the passenger ");
			scanf("%d",&s[i].age);
		printf("\nenter the fare to collect ");
			scanf("%d",&s[i].fare);
		printf("\nenter the gender of passenger ");
			scanf("%c",&s[i].gender);

		if(s[i].gender=='m')
		{
			sum=sum+s[i].fare;
		}
	}
	printf("\nthe totale fare collected from male is : %d",sum);
return (0);
}

The program runs like this.

Code:

mann@Manish:~/Desktop$ cc struc.c -o struc
mann@Manish:~/Desktop$ ./struc

enter the age of the passenger 11

enter the fare to collect 222

enter the gender of passenger
enter the age of the passenger
mann@Manish:~/Desktop$ cc struc.c -o struc
mann@Manish:~/Desktop$ ./struc

enter the name of passenger Manish

enter the age of the passenger 25

enter the fare to collect 111

enter the gender of passenger
enter the name of passenger

I don't know why the program does not allow me to input for gender. that is it goes straight to name for next value for i.

Any suggesttions about where I am doing it wrong?

exvor · 05-13-2006, 03:35 PM

There is a newline that is being imputed in there. Its left over from the first scanf call when you hit enter to compleate putting in text.

i get around this by doing something like this

Code:

 

int d; 
char grab[10]; 

scanf("%s",grab); 
sscanf(grab,"%d",d);

that way the first scanf will grab everything includeing the /n charecter. then the second will scan though the array and get the correct value you wanted.

of course this is not full proof but it at least stops anything from being left in the stdin buffer.

manishsingh4u · 05-13-2006, 03:46 PM

Thanks exvor for your help.