1. watchA
https://docs.oracle.com/cd/E36784_01/html/E36873/libresolv-3lib.html
https://docs.oracle.com/cd/E36784_01/html/E36875/resolver-3resolv.html#REFMAN3Bresolver-3resolv
libresolv(3LIB) Name libresolv - resolver library Synopsis cc [ flag... ] file... –lresolv –lsocket –lnsl [ library... ] #include <sys/types.h> #include <netinet/in.h> #include <arpa/nameser.h> #include <resolv.h> #include <netdb.h>
2. example
#include <resolv.h>
#include <string.h>
int main(int argc, char **argv)
{
int len;
struct __res_state statp;
union msg {
uchar_t buf[NS_MAXMSG];
HEADER h;
} resbuf;
/* Initialize resolver */
memset(&statp, 0, sizeof(statp));
if (res_ninit(&statp) < 0) {
fprintf(stderr, "Can't initialize statp.\n");
return (1);
}
/*
* Turning on DEBUG mode keeps this example simple,
* without need to output anything.
*/
statp.options |= RES_DEBUG;
/* Search for A type records */
len = res_nsearch(&statp, "example.com", C_IN, T_A,
resbuf.buf, NS_MAXMSG);
if (len < 0) {
fprintf(stderr, "Error occured during search.\n");
return (1);
}
if (len > NS_MAXMSG) {
fprintf(stderr, "The buffer is too small.\n");
return (1);
}
/* ... Process the received answer ... */
/* Cleanup */
res_ndestroy(&statp);
return (0);
}