I/O problem in socket programming

[polarbear12345]

the program below is to print the IP address of the connected client on server side
however,cout and other C++ stream objects are not working..
however function:
ssize_t write(int fd, const void *buf, size_t count)
is working.....
plzz give me reasons for this odd behaviour and also a possible solution to write in a file the obtained IP address in the for(;;) loop below using C++ stream objects


#include<sys/socket.h>
#include<errno.h>
#include<sys/types.h>
#include<arpa/inet.h>
#include<stdlib.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<fstream>
#include<iostream>
#define TIME_TO_REFRESH_LOG 60
using namespace std;
int main()
{
int listenfd=socket(AF_INET,SOCK_STREAM,0);
if(listenfd==-1)
{
perror("server socket");
exit(1);
}
struct sockaddr_in servaddr;
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(9001);
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr))==-1)
{
perror("server bind");
exit(1);
}
if(listen(listenfd,128)==-1)
{
perror("server listen");
exit(1);
}
int connfd;
struct sockaddr_in cliaddr;
socklen_t clilen;
for(;;)
{
bzero(&cliaddr,sizeof(cliaddr));
clilen=sizeof(cliaddr);
connfd=accept(listenfd,(struct sockaddr*)&cliaddr,&clilen);
if(connfd==-1)
{
perror("server accept");
//continue;
}
char buf[100];
inet_ntop(AF_INET,&cliaddr.sin_addr,buf,sizeof(buf));
cout<<buf;//not working
write(1,buf,100);//working
close(connfd);
}
return 0;
}

[polarbear12345]

the program below is to print the IP address of the connected client on server side
however,cout and other C++ stream objects are not working..
however function:
ssize_t write(int fd, const void *buf, size_t count)
is working.....
plzz give me reasons for this odd behaviour and also a possible solution to write in a file the obtained IP address in the for(;;) loop below using C++ stream objects


#include<sys/socket.h>
#include<errno.h>
#include<sys/types.h>
#include<arpa/inet.h>
#include<stdlib.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<fstream>
#include<iostream>
#define TIME_TO_REFRESH_LOG 60
using namespace std;
int main()
{
int listenfd=socket(AF_INET,SOCK_STREAM,0);
if(listenfd==-1)
{
perror("server socket");
exit(1);
}
struct sockaddr_in servaddr;
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family=AF_INET;
servaddr.sin_port=htons(9001);
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr))==-1)
{
perror("server bind");
exit(1);
}
if(listen(listenfd,128)==-1)
{
perror("server listen");
exit(1);
}
int connfd;
struct sockaddr_in cliaddr;
socklen_t clilen;
for(;;)
{
bzero(&cliaddr,sizeof(cliaddr));
clilen=sizeof(cliaddr);//changed after below //discussion from clilen=0
connfd=accept(listenfd,(struct sockaddr*)&cliaddr,&clilen);
if(connfd==-1)
{
perror("server accept");
//continue;
}
char buf[100];
inet_ntop(AF_INET,&cliaddr.sin_addr,buf,sizeof(buf));
cout<<buf;//not working in loop
write(1,buf,100);//working
close(connfd);
}
return 0;
}

[dwhitney67]

An excerpt from the man-page for accept()...



...
The addrlen argument is a value-result argument: it should initially contain the size
of the structure pointed to by addr; on return it will contain the actual length
(in bytes) of the address returned. When addr is NULL nothing is filled in.

In your code, you set this value to a zero.

You then want to try something like:


const char* sourceAddr = inet_ntoa(addr.sin_addr);
const unsigned short sourcePort = ntohs(addr.sin_port);


P.S. Before you state it, I know... inet_ntoa() is considered deprecated.

[dwhitney67]

Btw, I tested a TCP server application using the inet_ntop(); the results are either wrong or totally misleading, or I just plain don't understand how to use that function.

Here's a snip of the code I tested with:


...
sockaddr_in addr;
socklen_t addrlen = sizeof(addr);

int clntSock = accept(sd, (sockaddr*) &addr, &addrlen);

std::cout << "client connected... ";
char buf[1000] = {0};

inet_ntop(AF_INET, &addr, buf, sizeof(buf));

std::cout << buf << std::endl;

const char* clntaddr = inet_ntoa(addr.sin_addr);
const unsigned short clntport = ntohs(addr.sin_port);

std::cout << "addr = " << clntaddr << ", port = " << clntport << std::endl;

close(clntSock);


The output I got was:


client connected... 2.0.169.203
addr = 127.0.0.1, port = 43467

[smartbei]

Maybe you need to give inet_ntop addr.sin_addr instead of addr?



inet_ntop(AF_INET, addr.sin_addr, buf, sizeof(buf));

[dwhitney67]

Maybe you need to give inet_ntop addr.sin_addr instead of addr?

Yes, thank you, that is correct. I should have paid more attention to the OP's code.

[polarbear12345]

well guys my problem is that when i use cout in above for(;;) loop no result is displayed each time a client connects....
Only when i use write() func result is displayed each time a client is connected...

above problem persists only when cout is used in a loop like above

plzzz help

[smartbei]

Maybe it is a buffering problem?

Try cout.flush()...

[dwhitney67]

well guys my problem is that when i use cout in above for(;;) loop no result is displayed each time a client connects....
Only when i use write() func result is displayed each time a client is connected...

above problem persists only when cout is used in a loop like above

plzzz help

Hopefully you heeded my advice from an earlier post. If not, please fix the following:


struct sockaddr_in cliaddr;
socklen_t clilen = sizeof(cliaddr); // <--- Here's the change


Btw, this code works:


for (;;)
{
int clntSock = accept(sd, (sockaddr*) &cliaddr, &clilen);

char buf[16] = {0};
const char* clntaddr = inet_ntop(AF_INET, &cliaddr.sin_addr, buf, sizeof(buf));
const unsigned short clntport = ntohs(cliaddr.sin_port);

std::cout << "addr = " << clntaddr << ", port = " << clntport << std::endl;

close(clntSock);
}

[polarbear12345]

i got it due to some reason cout buffer was not being flushed at required time
i used flush(cout)

[slavik]

threads merged.