problem with fifos linux
- by nunos
I am having problem debugging why n_bytes in read_from_fifo function in client.c doesn't correspond to the value written to the fifo. It should only write 25 bytes but it tries to read a lot more (1836020505 bytes (!) to be exact). Any idea why this is happening?
server.c:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <signal.h>
#include <pthread.h>
#include <sys/stat.h>
typedef enum { false, true } bool;
//first read the int with the number of bytes the data will have
//then read that number of bytes
bool read_from_fifo(int fd, char* var)
{
int n_bytes;
if (read(fd, &n_bytes, sizeof(int)))
{
printf("going to read %d bytes\n", n_bytes);
if (read(fd, var, n_bytes))
printf("read var\n");
else {
printf("error in read var. errno: %d\n", errno);
exit(-1);
}
}
return true;
}
int main()
{
mkfifo("/tmp/foo", 0660);
int fd = open("/tmp/foo", O_RDONLY);
char var[100];
read_from_fifo(fd, var);
printf("var: %s\n", var);
return 0;
}
client.c:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
typedef enum { false, true } bool;
//first write to fd a int with the number of bytes that will be written afterwards
bool write_to_fifo(int fd, char* data)
{
int n_bytes = (strlen(data)) * sizeof(char);
printf("going to write %d bytes\n", n_bytes);
if (write(fd, &n_bytes, sizeof(int) != -1))
if (write(fd, data, n_bytes) != -1)
return true;
return false;
}
int main()
{
int fd = open("/tmp/foo", O_WRONLY);
char data[] = "some random string abcdef";
write_to_fifo(fd, data);
return 0;
}
Help is greatly appreciated. Thanks in advance.
