en faite voila mon code :
char buffer[PACKET_SIZE +1];
readn(fin, buffer, PACKET_SIZE);

int readn(int fd, char *ptr, int n){
int nl, nr;
nl = n;
while ( nl > 0 ) {
printf("buffer size : %d\n",nl);
nr = read(fd,ptr,nl);
printf("point 1 : %s\n",ptr);
if (nr < 0 ) {
if ( nr == -1 ) {
*ptr = 0x00;
return (n-nl);
}
return nr; /*error*/
} else {
if ( nr == 0 )
break;
}
nl -= nr;
ptr += nr;
}
/*pointing ptr to the adress 0x00*/
*ptr = 0x00;
return (n-nl);