read from file using forks

Applications Programming
1

i'm tring to make 2 processes each read from the same file but only one of them read the file.

FILE * fileptr1;
fileptr1 = fopen("file1.txt","rt");
pid2=fork();
while(1)		
{
	fscanf(fileptr1,"%s",temp1);
	if(feof(fileptr1)==0)
	{
		printf("%i",getpid());	//id of current process 
		printf(" Read: ");
		printf("%s",temp1);	//what was just read
		printf("\n");		
	}
	else
		break;
}
if(pid2==0)
fclose(fileptr1);			//close reading file
2

go through this link

3

The file is available to both the processes after the fork call.
So most likely one of the process reads the file & the file offset is
updated , and the other process gets an EOF .
So only one process prints the contents .
May get the desired result with read system call since you can control the
number of bytes to be read .
Or may try with setting the buffering options with setbuf function.

4

i really can't use read do to the fact that i want it to read a whole line and all the lines aren't the same length. i got it to work using read but it didn't complete my objective to read line by line.

And i don't understand why one process gets an EOF. I thought they shared the same pointer?

5

this is what i have now still no idea why is doesn't work

#include <stdio.h>
#include <fcntl.h>
main( )
{
	FILE *fileptr;
	char temp1[100];
	char buff2[20];
	int pid2;
	FILE * fileptr1;
	fileptr1 = fopen("file1.txt","rt");
	pid2=fork();
	printf("%i",getpid());
	printf("just created \n");
	while(1)		
	{
		printf("%i",getpid());
		printf("in the while loop\n");
		fscanf(fileptr1,"%s",temp1);
		if(feof(fileptr1)==0)
		{
			printf("%i",getpid());	//id of current process 
			printf(" Read: ");
			printf("%s",temp1);	//what was just read
			printf("\n");
			sleep(5);		
		}
	else
		break;
	}
}

this was the output

26017just created 
26017in the while loop
26017 Read: m+n
26016just created 
26016in the while loop
26017in the while loop
26017 Read: o+p
26017in the while loop
26017 Read: q+r+s
26017in the while loop
26017 Read: a+b+c+d
26017in the while loop
6

I don't really have the foggiest idea of what you're actually trying to do here. But try this... open the file, then shut off buffering like this:

        fileptr1 = fopen("file1.txt","r");
        setvbuf(fileptr1, (char *)NULL, _IONBF, 0);
7

omg it works... !!!! wow thanks. all i want was for 2 processes to read from the same file one line at a time