c + shared memory

dilberim82 · 03-07-2005, 06:48 PM

Ok here i have a program thats supposed to compute the fibanocci sequence with a child & parent process. Does everything it is supposed to do but when i do ./fibMem X where X > 7, it cuts off the last two numbers. So my output for ./fibMem 9 is:

Ok, Child is done!
*1123581234

What am i doing wrong? and can i have spaces between so its easier to read instead of printing everything in one line?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/shm.h>
#include <sys/stat.h>

#define max_sequence 10

typedef struct{
	long fib_sequence[max_sequence];
	int sequence_size;
}shared_data;

void main(int argc, char *argv[])
{
	pid_t pid;
	int status;
	int m = 0;	
	long oldnum = 1;
	long curnum = 1;
	long nextnum, i;
	int num_counter = 0;
	char* shmem;			
	int segment;
	shared_data *sdptr;
	shared_data sd;
	int temp;
	
	if(argc < 2){
		printf("Invalid Number of Arguments\n");
		exit(0);
	}
	else 
		i = atoi(argv[1]);
	
	i =i - 1;

	if(i < 2 || i > max_sequence)
	{
		printf("Invalid Number \n");
		exit(2);
	}

	sd.sequence_size = i;

	segment = shmget(IPC_PRIVATE, sizeof(sd), S_IRUSR | S_IWUSR);
	
	shmem = (char*) shmat(segment, NULL, 0);

	switch(pid = fork())
	{
		case -1:
			perror("Fork Failed \n");
			break;
		case 0:
			sprintf(shmem, "%d%c ", oldnum, ' ');
			num_counter++;
			
			while(i > 0)
			{
				shmem++;
				sprintf(shmem, "%d ", curnum);
				nextnum = curnum + oldnum;
				oldnum = curnum;
				curnum = nextnum;
				i--;
			}
			printf("\n");
			exit(1);
			
		default:
			wait(&status);
			printf("Ok, Child is done! \n");
				printf("*%s \n", shmem);
			break; 
                }
}

jtshaw · 03-07-2005, 07:07 PM

Code:

switch (pid = fork()) {
        case -1:
                perror("Fork Failed \n");
                break;
        case 0:
                sprintf(shmem, "%s %ld", shmem,oldnum);
                num_counter++;

                while (i > 0) {
                        shmem++;
                        sprintf(shmem, "%s %ld", shmem,curnum);
                        nextnum = curnum + oldnum;
                        oldnum = curnum;
                        curnum = nextnum;
                        i--;
                }
                printf("\n");
                exit(1);

        default:
                wait(&status);
                printf("Ok, Child is done! \n");
                printf("*%s \n", shmem);
                break;
}

Ok, this example should both have spaces and not have the problems with your text being overwritten.

dilberim82 · 03-07-2005, 07:21 PM

Thanks jt,
That works

. And i figured out why you did it the way you did by reading the man pages. Thanks again...

jtshaw · 03-07-2005, 07:49 PM

Np, sorry, I ment to have more of an explination... but apparently I'm doing to many things at once.