program in c - error

[Piotr Kirklewski]

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;
}

[Hein van den Heuvel]

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

[Hein van den Heuvel]

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

[Piotr Kirklewski]

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

[Steven Schweda]

> 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?

[James R. Ferguson]

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...

[Steven Schweda · Accepted solution]

> 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.

[Steven Schweda]

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

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