C socket program error - c

Question

This is my C client code. Somehow it is not working. It worked when I tried with argument passing.
I want the program to ask user to give hostname then it will ask for portname and then the message to send:
Enter hostname: localhost
Enter portname: 56456
Enter message : Hi user
Enter message : What's up
Enter message : How are you
And once the host and port given it should not ask for again (until restart the program). I tried with do while loop, but it is not working.
On server it will display the sent message
Here is my code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
void error(const char *msg)
{
perror(msg);
exit(0);
}
//int main(int argc, char *argv[])
int main()
{
char *argv[256];
int argc;
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
printf("\n\nEnter Hostname\n\n");
fgets(argv[0],256,stdin);
char buffer[256];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
printf("Please enter the message: ");
bzero(buffer,256);
//buffer = tempFunc();
fgets(buffer,255,stdin);
printf("\n\nHere Goes the output\n%s",buffer);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}

Answer 1

First, do not use char * argv[256]
char buffer[256];
printf("\n\nEnter Hostname\n\n");
fgets(buffer,256,stdin);
Then check Removing trailing newline character from fgets() input to deal with fgets.
For an infinite loop, don't do
int a=2; // Useless declaration
do
{
// Your code
}while(a=2) // I guess you wanted (a == 2)
use:
while(1)
{
// Your code
}
Or
for(;;)
{
// Your code
}
It seems that you need a little bit of training, try some tutorials, look for good practices in C, enable warning flags on compilation and learn to use a debugger like gdb.
P.S:
https://stackoverflow.com/help/asking
https://stackoverflow.com/help/answering

Answer 2

Let's fix some basic things first.
Your argv was an array of pointers, pointing to some arbitrary place in memory, here your program could crash.
Next thing is, when you're reading input with fgets, you are reading the \n, too. So localhost\n isn't a valid hostname. Overwrite the last character with an binary zero, to remove the \n.
int main()
{
char hostname[256];
char port[16];
char buffer[256];
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
printf("\n\nEnter Hostname\n\n");
fgets(hostname, 256,stdin);
hostname[ strlen(hostname) - 1 ] = '\0';
fgets(port, 16, stdin);
port[ strlen(port) - 1] = '\0';
portno = atoi(port);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(hostname);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
//...
}

Answer 3

For command line argument you should not declare argc and argv again! Try this-
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
printf("Please enter the message: ");
bzero(buffer,256);
//buffer = tempFunc();
fgets(buffer,255,stdin);
printf("\n\nHere Goes the output\n%s",buffer);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}
and add the do while loop where you want!

Answer 4

Here is the code that works with loop. Thanks to #Coconop
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main()
{
char hostname[256];
char port[16];
char buffer[256];
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
printf("\n\nEnter Hostname\n\n");
fgets(hostname, 256,stdin);
hostname[ strlen(hostname) - 1 ] = '\0';
fgets(port, 16, stdin);
port[ strlen(port) - 1] = '\0';
portno = atoi(port);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(hostname);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
int a=2;
do {
printf("Please enter the message: ");
bzero(buffer,256);
//buffer = tempFunc();
fgets(buffer,255,stdin);
printf("\n\nHere Goes the output\n%s",buffer);
n = write(sockfd,buffer,strlen(buffer));
}while(a=2);
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}