#include <ev.h>
#include <stdio.h>

ev_io stdin_watcher;
ev_timer timeout_watcher;

static void stdin_cb(EV_P_ ev_io *w,int revents)
{
    puts ("stdin ready");
    ev_io_stop(EV_A_ w);
    ev_break (EV_A_ EVBREAK_ALL);
}

static void timeout_cb (EV_P_ ev_timer *w,int revents)
{
    puts ("timeout");
    ev_break( EV_A_ EVBREAK_ONE );
}

int main(int argc,char* argv[])
{
    struct ev_loop *loop = EV_DEFAULT;

    ev_io_init(&stdin_watcher,stdin_cb,0,EV_READ);
    ev_io_start (loop,&stdin_watcher);

    ev_timer_init (&timeout_watcher,timeout_cb,5.5,0); // in document the last is 0. not 0,I don‘t know why yet 
    ev_timer_start (loop,&timeout_watcher);

    ev_run (loop,0);

    return 0;
}

output:
root@debian:/home/xzc/cpp/test# gcc -o libev_hello libev_hello.c
/tmp/ccNN2QkE.o: In function `stdin_cb‘:
libev_hello.c:(.text+0x20): undefined reference to `ev_io_stop‘
libev_hello.c:(.text+0x33): undefined reference to `ev_break‘
/tmp/ccNN2QkE.o: In function `timeout_cb‘:
libev_hello.c:(.text+0x5a): undefined reference to `ev_break‘
/tmp/ccNN2QkE.o: In function `main‘:
libev_hello.c:(.text+0x71): undefined reference to `ev_default_loop‘
libev_hello.c:(.text+0xc9): undefined reference to `ev_io_start‘
libev_hello.c:(.text+0x11f): undefined reference to `ev_timer_start‘
libev_hello.c:(.text+0x133): undefined reference to `ev_run‘
collect2: ld returned 1 exit status