Lab46 Wiki

1. I/O Streams (cin, cout, cerr, stream operators) [C++]
2. Namespaces [C++]
3. Type Casting Operators, Const-Volatility Specifiers (const, volatile) [C++]
4. Classes (Objects, Constructor, Destructor, Access Control, Public, Protected, Private, Friend, “this” pointer) [C++]
5. Inheritance (single, multiple Inheritance), Polymorphism/Virtual Functions, Abstract Base Class [C++]
6. Overloading (Functions, Operators) [C++]
7. Exception Handing (throw, try, catch) [C++]
8. Templates, STL (Standard Template Library) [C++]

I/O Streams (cin, cout, cerr, stream operators)

The concepts of I/O in C++ are streams, insertion, and extraction. The input stream is a source of input. It can be an object from which characters can be obtained (extracted). The output stream is an object to where output can be directed.

Here is and example

#include <iostream>
#include <fstream>
 
int main () 
{
  ofstream myfile;
  myfile.open ("example.txt");
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

Namespaces [C++]

A namespace is a declaration of different areas of the code. It calls them by a name and is then called out from within the code within the cycle of workflow.

Here is an example of the arrangement that a namespace takes within the code.

#include <iostream>
using namespace std;
 
namespace first
{
  int var = 5;
}
 
namespace second
{
  double var = 3.1416;
}
 
int main () {
  cout << first::var << endl;
  cout << second::var << endl;
  return 0;
}

Classes

Classes are groups of data related to a single object type. They are really functions to access information, and the classes possess the ability to inherit from other classes.

Here is an example from wiki. This shows “class” being used to define the called variable “person”. Then person is further allocated to have two containers, a and b.

#include <iostream>
#include <string>
using namespace std;
 
class person
{
public:
  string name;
  int age;
};
 
int main()
{
  person a, b;
  a.name = "Calvin";
  b.name = "Hobbes";
  a.age = 30;
  b.age = 20;
  cout << a.name << ": " << a.age << endl;
  cout << b.name << ": " << b.age << endl;
  return 0;
}

Inheritance

Inheritance is a a structure of reusing existing classes that have already been declared without modifying them, thus producing hierarchical relationships between them.

In the following example the class “A” is called out as public making it inherit the past declaration.

#include <iostream>
using namespace std;
 
class A {
   int data;
public:
   void f(int arg) { data = arg; }
   int g() { return data; }
};
 
class B : public A { };
 
int main() {
   B obj;
   obj.f(20);
   cout << obj.g() << endl;
}

Overloading

Overloading allows functions to have the same name but to have different parameters. So operators can be extend to act as a class within the same code.

Here is an example from wiki. The “time” operators is declared at the code header and given meaning. It is then broken into minutes and seconds.

Time operator+(const Time& lhs, const Time& rhs) 
{
    Time temp = lhs;
    temp.seconds += rhs.seconds;
    if (temp.seconds >= 60) {
        temp.seconds -= 60;
        temp.minutes++;
    }
    temp.minutes += rhs.minutes;
    if (temp.minutes >= 60) {
        temp.minutes -= 60;
        temp.hours++;
    }
    temp.hours += rhs.hours;
    return temp;
}

Exception Handling

Exception Handling is the attempt to have foresight into problems that happen while the code is running. Planning ahead for the inability of the program to do what it is designed to do, like being unable to find the source file that is used to pull up a list of data. While righting you code it is a good idea to “throw and exception” and see how the code responds.

Here is an example where we are asking the user for two numbers… what if they add a letter?

	cout << "Please provide two numbers\n";
	cout << "First Number: ";
	cin >> a;
	cout << "Second Number: ";
	cin >> b;

Adding in an If statement when the input is used can handle this exception and have fun telling the user to go back to Kindergarten.

If (a='A')
   cout << "sorry bro...that is a letter.. and number is the ones you use when you count your pennys";

Templates, STL

STL is short for Standard Template Library. The templates are a standard list of classes and template code.

STL provides many different types of container types. One is called a vector. It is sets a block allocated for use and can grow as needed (something that would make bignum easier). Here is an example i found. You can see the used of the vector.h file and the allocating of it. “vector<int> v;”.

#include <string.h>
#include <algo.h>
#include <vector.h>
#include <stdlib.h>
#include <iostream.h>
 
main ()
{
  vector<int> v;  // create an empty vector of integers
  int input;
  while (cin >> input)    // while not end of file
    v.push_back (input);  // append to vector
 
  sort(v.begin(), v.end());
 
  int n = v.size();
  for (int i = 0; i < n; i++)
    cout << v[i] << "\n";
}

Use a C program to change the IP address of my computer.

While doing other objectives I came across the suggestion that you should change your IP at given increments to increases your privacy while surfing. The documentation i was reading had more to do with other “outlets” for creative computing; however my love of computers comes from finding the limits of what can or cannot be done.

Explore the world for a walk-through or community documentation. Compile that information and implement.

To change your ip the standard ifconfig way

# ifconfig eth0 192.168.1.5 netmask 255.255.255.0 up
# ifconfig eth0

Here is the direct code from lainoox that works very nicely. I would suggest that a script on playing with ifconfig would just be simpler. This is one approach.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <sys/ioctl.h>
#include <linux/sockios.h>
#include <errno.h>
#include <netinet/in.h>
#if defined(__GLIBC__) && __GLIBC__ >=2 && __GLIBC_MINOR__ >= 1
#include <netpacket/packet.h>
#include <net/ethernet.h>
#else
#include <sys/types.h>
#include <netinet/if_ether.h>
#endif
 
int set_ip(char *iface_name, char *ip_addr)
{
	if(!iface_name)
		return -1;	
 
	int sockfd;
	struct ifreq ifr;
	struct sockaddr_in sin;
 
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	if(sockfd == -1){
		fprintf(stderr, "Could not get socket.\n");
		return -1;
	}
 
	/* get interface name */
	strncpy(ifr.ifr_name, iface_name, IFNAMSIZ);
 
	/* Read interface flags */
	if (ioctl(sockfd, SIOCGIFFLAGS, &ifr) < 0) {
		fprintf(stderr, "ifdown: shutdown ");
		perror(ifr.ifr_name);
		return -1;
	}
 
	/*
	* Expected in <net/if.h> according to
	* "UNIX Network Programming".
	*/
	#ifdef ifr_flags
	# define IRFFLAGS       ifr_flags
	#else   /* Present on kFreeBSD */
	# define IRFFLAGS       ifr_flagshigh
	#endif
 
	// If interface is down, bring it up
	if (ifr.IRFFLAGS | ~(IFF_UP)) {
		fprintf(stdout, "Device is currently down..setting up.-- %u\n",ifr.IRFFLAGS);
		ifr.IRFFLAGS |= IFF_UP;
		if (ioctl(sockfd, SIOCSIFFLAGS, &ifr) < 0) {
			fprintf(stderr, "ifup: failed ");
			perror(ifr.ifr_name);
			return -1;
		}
	}
 
	sin.sin_family = AF_INET;
 
	// Convert IP from numbers and dots to binary notation
	inet_aton(ip_addr,&sin.sin_addr.s_addr);	
	memcpy(&ifr.ifr_addr, &sin, sizeof(struct sockaddr));	
 
	// Set interface address
	if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
		fprintf(stderr, "Cannot set IP address. ");
		perror(ifr.ifr_name);
		return -1;
	}	
	#undef IRFFLAGS		
 
	return 0;
}
 
void usage()
{
	const char *usage = {
		"./set_ip [interface] [ip address]\n"
	};
	fprintf(stderr,"%s",usage);
}
 
int main(int argc, char **argv)
{
	if(argc < 3){
		usage();
		return -1;
	}
 
	set_ip(argv[1],argv[2]);
 
	return 0;
}

Out put of the program

 ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:1b:21:0a:d2:cf  
          inet addr:192.168.5.12  Bcast:192.168.5.255  Mask:255.255.255.0
          inet6 addr: fe80::21b:21ff:fe0a:d2cf/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2690 errors:0 dropped:0 overruns:0 frame:0
          TX packets:14732 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:516826 (516.8 KB)  TX bytes:2242645 (2.2 MB)
 
$ sudo ./set_ip eth1 12.13.14.15
Device is currently down..setting up.-- 4163
$ ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:1b:21:0a:d2:cf  
          inet addr:12.13.14.15  Bcast:12.255.255.255  Mask:255.0.0.0
          inet6 addr: fe80::21b:21ff:fe0a:d2cf/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2690 errors:0 dropped:0 overruns:0 frame:0
          TX packets:14742 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:516826 (516.8 KB)  TX bytes:2247309 (2.2 MB

Here is a shell script route

#!/bin/bash
SUBNET=192.168.135.
ETH=eth0

for i in {1..254}
do
  ip addr add ${SUBNET}${i}/24 dev ${ETH}

  # do whatever you want here

  ip addr del ${SUBNET}${i}/24 dev ${ETH}
done

Sources

• http://www.cyberciti.biz/faq/linux-change-ip-address/
• http://www.lainoox.com/set-ip-address-c-linux/
• http://www.lainoox.com/linux-interface-configuration-ifconfig/
• http://www.ehow.com/how_2180157_change-ip-address-linux-shell.html

Reflect upon your results of the measurement to ascertain your achievement of the particular course objective.

• How did you do?
• Is there room for improvement?
• Could the measurement process be enhanced to be more effective?
• Do you think this enhancement would be efficient to employ?
• Could the course objective be altered to be more applicable? How would you alter it?