topic Re: program in c - error in Operating System - HP-UX

program in c - error

Piotr Kirklewski — Fri, 20 May 2011 04:55:26 GMT

I'm trying to compile the below program but there is an error:

gcc -o portcheck portcheck.c
portcheck.c: In function ‘main’:
portcheck.c:26: error: incompatible types when assigning to type ‘char[1023]’ from type ‘char *’

Please help
==============================================
#include
#include
#include

#include

#include

#include
#include
#include
#include
#include
#include
#include

int main(int argc, char **argv)
{
u_short port; /* user specified port number */
char addr[1023]; /* the address */
struct sockaddr_in address; /* address structures */
struct hostent *host_info; /* host info structure */
short int sock = -1; /* the socket descriptor */

port = atoi(argv[1]);
addr = strncpy(addr, argv[2], 1023);
bzero((char *)&address, sizeof(address)); /* init addr struct */
address.sin_addr.s_addr = inet_addr(addr); /* assign the address */
address.sin_port = htons(port); /* translate int2port num */

/*
* Three simple steps:
* 1. Open the master socket locally
* 2. Try to connect to hostbyport, if it works
* print the successful message.
* 3. If no route then complain with vulgarity
* (it is just a rapid prototype after all)
* Otherwise do nothing.
*/
sock = socket(AF_INET, SOCK_STREAM, 0);
if(connect(sock,(struct sockaddr *)&address,sizeof(address)) == 0)
printf("%i is open on %s\n", port, argv[2]);

if (errno == 113) fprintf(stderr, "F*^k - no route to host\n");

close(sock);

return 0;
}

Re: program in c - error

Hein van den Heuvel — Fri, 20 May 2011 05:12:57 GMT

In the line 26 you have addr as input as ouput:

addr = strncpy(addr, argv[2], 1023);

It is not a proper L value valid for output as provided.
Just drop it and use only:

strncpy(addr, argv[2], 1023);

If you need the output then you need something like:

char *p;
:
p = strncpy(addr, argv[2], 1023);

hth,
Hein

Re: program in c - error

Hein van den Heuvel — Sat, 21 May 2011 17:43:45 GMT

Hmm, 5/10. Did the reply not address the problem for which you asked for help?
Is there an other problem? Do explain.
Or just fat fingered the assignment? Just close.

Cheers,
Hein

Re: program in c - error

Piotr Kirklewski — Sat, 21 May 2011 18:08:20 GMT

Thanks
Now it compiles fine but it always says the host is active even if there is no such IP in the network.
What would be the reason for that ?
Reagrds
Peter

Re: program in c - error

Steven Schweda — Sat, 21 May 2011 20:03:28 GMT

> What would be the reason for that ?

Uh, bad code?

> sock = socket(AF_INET, SOCK_STREAM, 0);

Did that work? How would you know?

> if (errno == 113) fprintf(stderr, "F*^k - no route to host\n");

How does that help you for any other value of
errno?

man strerror

> return 0;

Always? How informative is that?

Re: program in c - error

James R. Ferguson — Sat, 21 May 2011 21:20:54 GMT

Hi:

Do you mean to do something like this (replace the body of your code with this)?

...
sock = socket(AF_INET, SOCK_STREAM, 0);
if (bind(sock,(struct sockaddr *)&address,sizeof(address)) == -1) {
perror("bind");
exit(1);
}
if (connect(sock,(struct sockaddr *)&address,sizeof(address)) == -1) {
perror("connect");
exit(1);
}
printf("%i is open on %s\n", port, argv[2]);
close(sock);
exit(0);
}

Now, if I compile and run this like:

# ./a.out 22 127.0.0.1
bind: Address already in use
# ./a.out 123 127.0.0.1
123 is open on 127.0.0.1

Better?

Regards!

...JRF...

Re: program in c - error

Steven Schweda — Sat, 21 May 2011 23:02:23 GMT

> Do you mean to do something like this
> [...]?

I was guessing more like this:

alp $ type portcheck.c
#include
#include
#include

#include

#include

#include
#include
#include
#include
#include
#include
#include

int main(int argc, char **argv)
{
u_short port; /* user specified port number */
struct sockaddr_in address; /* address structures */
struct hostent *host_info; /* host info structure */
short int sock = -1; /* the socket descriptor */
int sts = 0;

if (argc != 3)
exit( EINVAL);

port = atoi(argv[1]);
bzero((char *)&address, sizeof(address)); /* init addr struct */
address.sin_addr.s_addr = inet_addr(argv[2]); /* assign the address */
address.sin_port = htons(port); /* translate int2port num */
address.sin_family = AF_INET; /* Address family. */

sock = socket( address.sin_family, SOCK_STREAM, 0);
if (sock < 0)
{
fprintf( stderr, " socket(): %s\n", strerror( errno));
sts = errno;
}
else
{
if (connect( sock, (struct sockaddr *)&address, sizeof(address)) == 0)
{
fprintf( stderr, "Port %d is open on %s.\n", port, argv[2]);
}
else
{
fprintf( stderr, " connect(): %s\n", strerror( errno));
sts = errno;
}
close(sock);
}
exit( sts);
}

alp $ cc portcheck /define = (_POSIX_EXIT)
alp $ link portcheck
alp $ exec portcheck 80 10.0.0.9
Port 80 is open on 10.0.0.9.
alp $ exec portcheck 81 10.0.0.9
connect(): connection refused

I don't write enough socket code to know
much, but I can find plenty of good code from
which to steal some working bits.

Re: program in c - error

Steven Schweda — Sun, 22 May 2011 01:01:20 GMT

> Hmm, 5/10. [...]

Smug ingratitude from the helpless is what
makes Forum participation so satisfying for
me.