This code works perfectly on Linux, but returns the error "gethostbyname: Undefined error: 0" in the terminal. I have also tried other codes from the net, but all of them either return some error during compilation or display the IPv4 address as 0.0.0.0. Is there anything I can do to make this work?
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
void checkHostName(int hostname)
{
if (hostname == -1) {
perror("gethostname");
exit(1);
}
}
void checkHostEntry(struct hostent* hostentry)
{
if (hostentry == NULL) {
perror("gethostbyname");
exit(1);
}
}
void checkIPbuffer(char* IPbuffer)
{
if (NULL == IPbuffer) {
perror("inet_ntoa");
exit(1);
}
}
int main()
{
char hostbuffer[256];
char* IPbuffer;
struct hostent* host_entry;
int hostname;
hostname = gethostname(hostbuffer, sizeof(hostbuffer));
checkHostName(hostname);
host_entry = gethostbyname(hostbuffer);
checkHostEntry(host_entry);
IPbuffer = inet_ntoa(*((struct in_addr*) host_entry->h_addr_list[0]));
printf("Hostname: %s\n", hostbuffer);
printf("Host IP: %s", IPbuffer);
return 0;
}
Related
When I was writing twitter console application, I faced a problem with C function gethostbyname(). Twitter API offers to connect to https://api.twitter.com/oauth2/token , but when I tried to get IP by that function, it returned NULL. Curl resolves URL fine, and I don't think that's there is problem with DNS. Connected code is same as I've tried that doesn't work properly too.
P.S. Maybe my problem is very obvious, but I wasted at least 7 hour without any changes in code, just trying to find an answer.
#include <stdio.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
int i;
struct hostent *he;
struct in_addr **addr_list;
if (argc != 2) {
fprintf(stderr,"usage: ghbn hostname\n");
return 1;
}
if ((he = gethostbyname(argv[1])) == NULL) { // get the host info
herror("gethostbyname");
return 2;
}
// print information about this host:
printf("Official name is: %s\n", he->h_name);
printf(" IP addresses: ");
addr_list = (struct in_addr **)he->h_addr_list;
for(i = 0; addr_list[i] != NULL; i++) {
printf("%s ", inet_ntoa(*addr_list[i]));
}
printf("\n");
return 0;
}
i'm writing a server/client c program based on AX.25 protocol.
The server creating the socket, binding Successfully and listening for coming connections.
the client running in a different thread but fails on connect with " No route to host"
Server code
#include <sys/socket.h>
#include <netax25/ax25.h>
#include <netax25/axlib.h>
#include <netax25/axconfig.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <syslog.h>
#include <sys/types.h>
#include <linux/socket.h>
#include <stdlib.h>
#include <sys/un.h>
#include <string.h>
#include <errno.h>
int main(int argc,char **argv,char **envp) {
int ax25_socket = -1;
unsigned char buffer[512];
struct full_sockaddr_ax25 addr, axconnect ;
char *port ="3";// sm0 port number:3
char *call = "OH2BNS-8";// sm0 callsign
bzero((char *) &addr, sizeof(struct full_sockaddr_ax25));
addr.fsa_ax25.sax25_family = AF_AX25;
addr.fsa_ax25.sax25_ndigis = 1;
if (ax25_config_load_ports() == 0) {
printf( "Problem with axports file");
//return -1;
}
char* ax25port = (char*) ax25_config_get_addr(port);
ax25_aton_entry( call, addr.fsa_ax25.sax25_call.ax25_call);
ax25_aton_entry( ax25port, addr.fsa_digipeater[0].ax25_call);
ax25_socket = socket(AF_AX25, SOCK_SEQPACKET, 0);
if (ax25_socket < -1)
printf( "error in create socket");
if (bind(ax25_socket, (struct sockaddr *)&addr, sizeof(struct full_sockaddr_ax25)) < 0) {
perror("bind--");
return -1;
}
if(listen(ax25_socket,2) != 0)
{
printf("cannot listen on socket!\n");
close(ax25_socket);
return 0;
}
puts("listening");
//bzero((char *) &axconnect, sizeof(struct full_sockaddr_ax25));
int len =sizeof(struct full_sockaddr_ax25);
int temp_sock_desc = accept(ax25_socket, (struct sockaddr*)&axconnect, &len);
if (temp_sock_desc == -1)
{
printf("cannot accept client!\n");
close(ax25_socket);
return 0;
}
return 0;
}
Client code
#include <sys/socket.h>
#include <netax25/ax25.h>
#include <netax25/axlib.h>
#include <netax25/axconfig.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <syslog.h>
#include <sys/types.h>
#include <linux/socket.h>
#include <stdlib.h>
#include <sys/un.h>
#include <string.h>
#include <errno.h>
int main(int argc, char *argv[])
{
int ax25_socket = -1;
unsigned char buffer[512];
struct full_sockaddr_ax25 axconnect ;
char *port ="3";// sm0 port number:3
char *call ="OH2BNS-8";// sm0 callsign
bzero((char *) &axconnect, sizeof(struct full_sockaddr_ax25));
axconnect.fsa_ax25.sax25_family = AF_AX25;
axconnect.fsa_ax25.sax25_ndigis = 1;
if (ax25_config_load_ports() == 0) {
printf( "Problem with axports file");
//return -1;
}
char* ax25port = (char*) ax25_config_get_addr(port);
ax25_aton_entry( call, axconnect.fsa_ax25.sax25_call.ax25_call);
ax25_aton_entry( ax25port, axconnect.fsa_digipeater[0].ax25_call);
ax25_socket = socket(AF_AX25, SOCK_SEQPACKET, 0);
if (ax25_socket < -1)
printf( "error in create socket");
if (connect(ax25_socket, (struct sockaddr *)&axconnect, sizeof(struct full_sockaddr_ax25)) != 0) {
perror("--");
switch (errno) {
case ECONNREFUSED:
printf("*** Connection refused\r");
break;
case ENETUNREACH:
printf("*** No known route\r");
break;
case EINTR:
printf("*** Connection timed out\r");
break;
default:
printf("ERROR: cannot connect to AX.25 callsign\r");
break;
}
close(ax25_socket);
}
printf("Connected!!\r");
int n = write(ax25_socket,"Message!!!!",18);
if(n = -1)
{
perror("write--");
}
return 0;
}
Simply put, a " No route to host"" would mean that there is no route for the server IP address in the client's routing table. Are you able to ping the server's IP address? Most likely you should not be able to and ping should say that the server is not reachable. If so, then this error has nothing to do with your program, you are probably running into a connectivity issue.
Can you find the entry for your server in the output of "route -n". If there is none, then you should check for a bigger prefix for the subnet of the server. If that also is not present, then you should confirm that you have a default route setup.
To further confirm, I would do the following two tests. First, what happens if you try to run the client/server on the same box? Second, what happens if you try to run the client/server on two boxes (present in the same subnet) and on the same LAN? If you do not see this issue and your application works just fine, then this should confirm that you are running into a connectivity issue.
I know this is an old question, but I would suspect a problem with ax25port - should be something like YOURCALL-0 where YOURCALL matches the HWaddr of an existing ax25 port ( try /sbin/ifconfig | fgrep AX.25
I am new with OpenCV.I've implemented a Stop and Wait protocol,in the sender I used OpenCV to capture frames from a webcam send them to a receiver and I'm having a problem using camera with OpenCV in the receiver with the received frames.I receive the error :
OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file /home/mihai/OpenCV-2.4.1/modules/core/src/array.cpp, line 2482
terminate called after throwing an instance of 'cv::Exception'
what(): /home/mihai/OpenCV-2.4.1/modules/core/src/array.cpp:2482: error: (-206) Unrecognized or unsupported array type in function cvGetMat
send.c
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "lib.h"
#include "cv.h"
#include "highgui.h"
#define HOST "127.0.0.1"
#define PORT 10000
int main(int argc, char *argv[])
{
msg t;
my_pkt p;
int fd, count, filesize;
struct stat f_status;
char buffer[MSGSIZE];
init(HOST, PORT);
printf("[SENDER] Server rocks.\n");
printf("[SENDER] File to send: %s\n", argv[1]);
CvCapture* capture = cvCaptureFromCAM( CV_CAP_ANY );
if(!capture) {
fprintf(stderr, "ERROR:capture is null\n" );
getchar();
return -1;
}
printf("[SERVER] File transfer begins.\n");
while(1) {
IplImage* frame = cvQueryFrame(capture);
if(!frame) {
fprintf(stderr,"ERROR:frame is null...\n");
getchar();
break;
}
memset(t.payload, 0, sizeof(t.payload));
memset(p.payload, 0, sizeof(p.payload));
p.type = TYPE3;
memcpy(p.payload, frame, 8);
t.len = 8;
memcpy(t.payload, &p, t.len);
send_message(&t);
if (recv_message(&t) < 0) {
perror("[SENDER] Receive error");
return -1;
}
p = *((my_pkt *) t.payload);
if (p.type != TYPE4) {
perror("[SENDER] Receive error");
return -1;
}
}
cvReleaseCapture( &capture );
printf("[SERVER] File transfer has ended.\n");
close(fd);
return 0;
}
recv.c
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include "cv.h"
#include "highgui.h"
#include "lib.h"
#define HOST "127.0.0.1"
#define PORT 10001
int main(void)
{
msg t;
my_pkt p;
int filesize, read_so_far, fd;
char filename[MSGSIZE];
init(HOST, PORT);
printf("[RECEIVER] Client rocks.\n");
cvNamedWindow( "camera_jigodiei", CV_WINDOW_AUTOSIZE );
/* Wait for file contents - TYPE 3 messages */
printf("[RECEIVER] Gonna wait for file chunks.\n");
while (1) {
memset(t.payload, 0, sizeof(t.payload));
if (recv_message(&t) < 0) {
perror("[RECEIVER] Receive message");
return -1;
}
p = *((my_pkt*) t.payload);
IplImage* frame=malloc(sizeof(p.payload) );
memmove(frame,&p,sizeof(p.payload) );
if ( !frame ) {
fprintf( stderr, "ERROR: frame is null...\n" );
getchar();
break;
}
cvShowImage( "camera_jigodiei", frame );//HERE I HAVE THE ERROR****
memset(t.payload, 0, sizeof(t.payload));
memset(p.payload, 0, sizeof(p.payload));
p.type = TYPE4;
memcpy(p.payload, ACK_T3, strlen(ACK_T3));
t.len = strlen(p.payload) + sizeof(int);
memcpy(t.payload, &p, t.len);
send_message(&t);
if ( (cvWaitKey(10) & 255) == 27 ) break;
}
cvDestroyWindow( "camera_jigodiei" );
printf("[RECEIVER] All done.\n");
close(fd);
return 0;
}
I've verified that the sender-receiver works sending and receiving the frames and they do.The problem is with OpenCV
gethostbyname works fine in fedora 32 bit but is failing on 64 bit environment giving a segmentation fault? In such scenario what is the problem and how can we resolve it?
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <netinet/in.h>
struct hostent *he;
struct in_addr a;
int main (int argc, char **argv) {
if (argc != 2) {
fprintf(stderr, "usage: %s hostname\n", argv[0]);
return 1;
}
he = gethostbyname (argv[1]);
if (he) {
printf("name :- %s\n", he->h_name);
while (*he->h_aliases)
printf("alias:- %s\n", *he->h_aliases++);
while (*he->h_addr_list) {
bcopy(*he->h_addr_list++, (char *) &a, sizeof(a));
printf("address:- %s\n", inet_ntoa(a));
}
}
else
herror(argv[0]);
return 0;
}
You are missing the correct includes:
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
Without the correct includes, inet_ntoa is assumed to have a return type of int. Because int has the same size as char* on x86, there is no problem. This is not true on x86_64, so the read of that string by printf causes a fault.
How can I get the IPv4 address of an interface on Linux from C code?
For example, I'd like to get the IP address (if any) assigned to eth0.
Try this:
#include <stdio.h>
#include <unistd.h>
#include <string.h> /* for strncpy */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>
int
main()
{
int fd;
struct ifreq ifr;
fd = socket(AF_INET, SOCK_DGRAM, 0);
/* I want to get an IPv4 IP address */
ifr.ifr_addr.sa_family = AF_INET;
/* I want IP address attached to "eth0" */
strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1);
ioctl(fd, SIOCGIFADDR, &ifr);
close(fd);
/* display result */
printf("%s\n", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));
return 0;
}
The code sample is taken from here.
In addition to the ioctl() method Filip demonstrated you can use getifaddrs(). There is an example program at the bottom of the man page.
If you're looking for an address (IPv4) of the specific interface say wlan0 then
try this code which uses getifaddrs():
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[])
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NI_MAXHOST];
if (getifaddrs(&ifaddr) == -1)
{
perror("getifaddrs");
exit(EXIT_FAILURE);
}
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
{
if (ifa->ifa_addr == NULL)
continue;
s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if((strcmp(ifa->ifa_name,"wlan0")==0)&&(ifa->ifa_addr->sa_family==AF_INET))
{
if (s != 0)
{
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\tInterface : <%s>\n",ifa->ifa_name );
printf("\t Address : <%s>\n", host);
}
}
freeifaddrs(ifaddr);
exit(EXIT_SUCCESS);
}
You can replace wlan0 with eth0 for ethernet and lo for local loopback.
The structure and detailed explanations of the data structures
used could be found here.
To know more about linked list in C this page will be a good starting point.
My 2 cents: the same code works even if iOS:
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
showIP();
}
void showIP()
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NI_MAXHOST];
if (getifaddrs(&ifaddr) == -1)
{
perror("getifaddrs");
exit(EXIT_FAILURE);
}
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
{
if (ifa->ifa_addr == NULL)
continue;
s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if( /*(strcmp(ifa->ifa_name,"wlan0")==0)&&( */ ifa->ifa_addr->sa_family==AF_INET) // )
{
if (s != 0)
{
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\tInterface : <%s>\n",ifa->ifa_name );
printf("\t Address : <%s>\n", host);
}
}
freeifaddrs(ifaddr);
}
#end
I simply removed the test against wlan0 to see data.
ps You can remove "family"
I have been in the same issue recently, and this is the code I made up and it works. Make sure to use the name of the network interface, exactly as you have it (could be "eth0" or else).
gotta check if ifconfigcommand beforehand to get the interface name and use it in C.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <unistd.h>
#include <linux/if.h>
#include <errno.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <arpa/inet.h>
void extract_ipaddress()
{
//create an ifreq struct for passing data in and out of ioctl
struct ifreq my_struct;
//declare and define the variable containing the name of the interface
char *interface_name="enp0s3"; //a very frequent interface name is "eth0";
//the ifreq structure should initially contains the name of the interface to be queried. Which should be copied into the ifr_name field.
//Since this is a fixed length buffer, one should ensure that the name does not cause an overrun
size_t interface_name_len=strlen(interface_name);
if(interface_name_len<sizeof(my_struct.ifr_name))
{
memcpy(my_struct.ifr_name,interface_name,interface_name_len);
my_struct.ifr_name[interface_name_len]=0;
}
else
{
perror("Copy name of interface to ifreq struct");
printf("The name you provided for the interface is too long...\n");
}
//provide an open socket descriptor with the address family AF_INET
/* ***************************************************************
* All ioctl call needs a file descriptor to act on. In the case of SIOCGIFADDR this must refer to a socket file descriptor. This socket must be in the address family that you wish to obtain (AF_INET for IPv4)
* ***************************************************************
*/
int file_descriptor=socket(AF_INET, SOCK_DGRAM,0);
if(file_descriptor==-1)
{
perror("Socket file descriptor");
printf("The construction of the socket file descriptor was unsuccessful.\n");
return -1;
}
//invoke ioctl() because the socket file descriptor exists and also the struct 'ifreq' exists
int myioctl_call=ioctl(file_descriptor,SIOCGIFADDR,&my_struct);
if (myioctl_call==-1)
{
perror("ioctl");
printf("Ooops, error when invoking ioctl() system call.\n");
close(file_descriptor);
return -1;
}
close(file_descriptor);
/* **********************************************************************
* If this completes without error , then the hardware address of the interface should have been returned in the 'my_struct.ifr_addr' which is types as struct sockaddr_in.
* ***********************************************************************/
//extract the IP Address (IPv4) from the my_struct.ifr_addr which has the type 'ifreq'
/* *** Cast the returned address to a struct 'sockaddr_in' *** */
struct sockaddr_in * ipaddress= (struct sockaddr_in *)&my_struct.ifr_addr;
/* *** Extract the 'sin_addr' field from the data type (struct) to obtain a struct 'in_addr' *** */
printf("IP Address is %s.\n", inet_ntoa(ipaddress->sin_addr));
}
If you don't mind the binary size, you can use iproute2 as library.
iproute2-as-lib
Pros:
No need to write the socket layer code.
More or even more information about network interfaces can be got. Same functionality with the iproute2 tools.
Simple API interface.
Cons:
iproute2-as-lib library size is big. ~500kb.
I found a quite easy way to get ip, by take advantage of using bash command:
hostname -I
but use "hostname -I" natively will print the result on screen, we need to use "popen()" to read result out and save it into a string, here is c code:
#include <stdio.h> // popen
#include "ip_common_def.h"
const char * get_ip()
{
// Read out "hostname -I" command output
FILE *fd = popen("hostname -I", "r");
if(fd == NULL) {
fprintf(stderr, "Could not open pipe.\n");
return NULL;
}
// Put output into a string (static memory)
static char buffer[IP_BUFFER_LEN];
fgets(buffer, IP_BUFFER_LEN, fd);
// Only keep the first ip.
for (int i = 0; i < IP_BUFFER_LEN; ++i)
{
if (buffer[i] == ' ')
{
buffer[i] = '\0';
break;
}
}
char *ret = malloc(strlen(buffer) + 1);
memcpy(ret, buffer, strlen(buffer));
ret[strlen(buffer)] = '\0';
printf("%s\n", ret);
return ret;
}