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// file: listener-async.c
//
// This program demonstrates how to use LCM in a select-based event loop where
// the program has other things to do while waiting for LCM messages (e.g.,
// periodically transmit messages of its own).
//
// To use LCM in another event loop (e.g., the GTK+ or QT event loops), see the
// API documentation on how to use file descriptors with the corresponding
// event loop.
//
// compile with:
// $ gcc -o listener-async listener-async.c -llcm
//
// On a system with pkg-config, you can also use:
// $ gcc -o listener-async listener-async.c `pkg-config --cflags --libs lcm`
#include <stdio.h>
#include <inttypes.h>
#include <sys/select.h>
#include <lcm/lcm.h>
#include "exlcm_example_t.h"
static void
my_handler(const lcm_recv_buf_t *rbuf, const char * channel,
const exlcm_example_t * msg, void * user)
{
int i;
printf("Received message on channel \"%s\":\n", channel);
printf(" timestamp = %"PRId64"\n", msg->timestamp);
printf(" position = (%f, %f, %f)\n",
msg->position[0], msg->position[1], msg->position[2]);
printf(" orientation = (%f, %f, %f, %f)\n",
msg->orientation[0], msg->orientation[1], msg->orientation[2],
msg->orientation[3]);
printf(" ranges:");
for(i = 0; i < msg->num_ranges; i++)
printf(" %d", msg->ranges[i]);
printf("\n");
printf(" name = '%s'\n", msg->name);
printf(" enabled = %d\n", msg->enabled);
}
int
main(int argc, char ** argv)
{
lcm_t * lcm;
lcm = lcm_create(NULL);
if(!lcm)
return 1;
exlcm_example_t_subscription_t * sub =
exlcm_example_t_subscribe(lcm, "EXAMPLE", &my_handler, NULL);
while(1) {
// setup the LCM file descriptor for waiting.
int lcm_fd = lcm_get_fileno(lcm);
fd_set fds;
FD_ZERO(&fds);
FD_SET(lcm_fd, &fds);
// wait a limited amount of time for an incoming message
struct timeval timeout = {
1, // seconds
0 // microseconds
};
int status = select(lcm_fd + 1, &fds, 0, 0, &timeout);
if(0 == status) {
// no messages
printf("waiting for message\n");
} else if(FD_ISSET(lcm_fd, &fds)) {
// LCM has events ready to be processed.
lcm_handle(lcm);
}
}
exlcm_example_t_unsubscribe(lcm, sub);
lcm_destroy(lcm);
return 0;
}