Merging “C” module into C++ project

Step -1

   Compile the C module alone with C++ compiler. For that we can put the following line in top and bottom of the file

// In the top of the file
#ifdef __cplusplus
extern "C" {
#endif
// in the bottom
#ifdef __cplusplus
}
#endif

OR

If you have only one header file going to include in C++ module than,
extern "C" {
// Get declaration for fun(int i, char c, float x)
#include "C_MOD_code.h"
}

Step-2
If the C module going to access the functions from C++ module, then declare like below
extern "C" void fun(int i, char c, float x);

step-3
Once the compilation get successes than link with C++ linker

Call the destructor more than one time

we can call the destructor as like function, but we can't call the constructor like this.

class Shape
{
   public:
       Shape(){ cout<<" Shape"<
       virtual ~Shape(){ cout<<" ~  Shape"<
};
class Circle : public Shape
{
   public:
      Circle() { cout<<"Circle"<< endl; }
      ~Circle(){ cout<<" ~ Circle" << endl; }
};

int main()
{

   Circle *ptr = new Circle();
   ptr->~Circle();
   ptr->~Circle();

   return 1;
}

output:-

# ./a.out

 Shape

Circle

 ~ Circle

 ~  Shape

 ~  Shape

while calling the destructor function first time , its calling the base call destructor also ( if its virtual ) . but after that not calling the base class destructor.

How to resolve the IPv6 Address from domain name in C++ ?

In general, we are using gethostbyname or gethostbyname_r for resolving IPAddress from domain name. These system calls are not supporting IPv6 format.

For resolve IPv6Address from domain name, we need to use gethostbyname2_r function.

struct in6_addr aadrv6;
struct hostent *host;
char* pszHostName = “localhost6.localdomain6”;
char strIPAddr[50];
char buffer[2048];
int iError = 0,hrr;

iError = gethostbyname2_r( pszHostName, AF_INET6, &hostbuf,buffer, 2048,&host,&hrr );

if( iError == 0 && host != NULL )
{
    memcpy( &aadrv6 , host->h_addr_list[0], sizeof( in6_addr ) );
   if( inet_ntop ( AF_INET6, &aadrv6, strIPAddr, INET6_ADDRSTRLEN ) != NULL )
   {
        printf("IPv6Address: %s\n", strIPAddr);
    }
}

output:
#./a.out
IPv6Address: ::1

In Linux anything is equivalent to windows registry?

I saw the questions in many Linux forums

The RPM package information stored in the below location

/var/lib/rpm

[root@hostrpm]# ls

Basenames     __db.000  __db.002  Dirnames  Group       Name      Providename     Pubkeys      Requireversion  Sigmd5

Conflictname  __db.001  __db.003  Filemd5s  Installtid  Packages  Provideversion  Requirename  Sha1header      Triggername

It uses Berkeley DB as its back-end. It consists of a single database (Packages) containing all of the meta information of the installed rpms.
The RPM database is used to keep track of all files that are changed and created when a user installs a package. If the database gets corrupted, the index databases can be recreated with the rpm --rebuilddb command.

If you issues the rpm- qa ( query ) command then, it will read from the DB and list out the package names.

If you delete the installation directory directly, it won’t delete the record from the RPM DB. For that you need to execute the rpm –ivh (uninstall ) command , otherwise you can’t install the same package.

How to check CPU and memory Hardware detials in RHEL system?

Using the bellow command, we can see the Memory and CPU related hardware details

#cat  /proc/meminfo


#cat  /proc/cpuinfo

How to write / setup SCTP client server program in RHEL system?

Setup:

Before run any SCTP application, we need to install SCTP libs from

http://lksctp.sourceforge.net/

Using the below command, register the SCTP module into kernel.

#modprobe sctp

http://linux.about.com/od/commands/l/blcmdl8_modprob.htm

SCTP Application writing:-

SCTP client and server system call follow same as TCP. ( like socket,bind,listen and accept )

Creating SCTP socket

Sock = socket( AF_INET, SOCK_STREAM, IPPROTO_SCTP );

Before listen, we need to set the value for the no.of stream for the socket using setsockopt system call.

struct sctp_initmsg startupsctp;

startupsctp.sinit_num_ostreams = 3;

startupsctp.sinit_max_instreams = 3;

startupsctp.sinit_max_attempts = 4;

ret = setsockopt( listen_Socket, IPPROTO_SCTP, SCTP_INITMSG, & startupsctp, sizeof(startupsctp) );

Using sctp_sendmsg() and sctp_recvmsg() system calls , we can send/receive data over the SCTP socket.

Example code:-

Please refer : http://www.ibm.com/developerworks/linux/library/l-sctp/

How to decompress the tar.bz2 format file?

#tar -xvjf xxxx.tar.bz2
tmp/test.txt

Options:

* x - extract
* c - create to create
* v - verbose
* z - gzip
* j - bzip2 ( .bz2 )
* f - file name ( after the “f” indicate the input/output file name )