isNumeric()

For some reason many C++ programmers believe there is an isNumeric() function available as part of the language. In fact I was searching for the header file to include to get a piece of code to work.

Its not difficult to create a function that will be able to check if the string is numeric or not. Here is the code.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include <iostream>
#include <string>
#include <sstream>

using namespace std;
 
bool isNumeric1(string stringToCheck)
{
  bool numeric = false;
 
  if(stringToCheck.find_first_not_of("0123456789.") == string::npos)
    numeric = true;
 
  return numeric;
}
 
bool isNumeric2(string stringToCheck)
{
  bool numeric = true;
  unsigned i = 0;
 
  while(numeric && i < stringToCheck.length())
  {
    switch (stringToCheck[i])
    {
    case '0': case '1': case '2': case '3': case '4': case '5': 
    case '6': case '7': case '8': case '9': case '.':
      //do nothing
      break;
    default:
      numeric = false;
    }
    i++;
  }
 
  return numeric;
}
 
bool isNumeric3(string stringToCheck)
{
  stringstream streamVal(stringToCheck);
  double tempVal;
 
  streamVal >> tempVal; //If numeric then everything transferred to tempVal

  if(streamVal.get() != EOF)
    return false;
  else
    return true;
}
 
int main()
{
  string str1("123"), str2("134.567"), str3("12AB");
  cout << "Approach 1" << endl;
  cout << str1 << (isNumeric1(str1) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str2 << (isNumeric1(str2) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str3 << (isNumeric1(str3) ? " is Numeric" : " is Not Numeric") << endl;
 
  cout << "\nApproach 2" << endl;
  cout << str1 << (isNumeric2(str1) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str2 << (isNumeric2(str2) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str3 << (isNumeric2(str3) ? " is Numeric" : " is Not Numeric") << endl;
 
  cout << "\nApproach 3" << endl;
  cout << str1 << (isNumeric3(str1) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str2 << (isNumeric3(str2) ? " is Numeric" : " is Not Numeric") << endl;
  cout << str3 << (isNumeric3(str3) ? " is Numeric" : " is Not Numeric") << endl;
 
  return 0;
}
 

Output is as follows:

There are few problems in the program above:

1. It does not cater for negative numbers

2. It will return wrong result when you have incorrect string like 12.34.56.78

I have intentionally left it as an exercise.

Other approaches are possible as well. Why not try and think of an approach yourself.

Switch Case using string

When I started thinking of this example, I also faced some of the other problems that I have encountered in my initial days of C++. One of these problems was how to convert String to multiple Ints and how to split strings easily, etc. Hopefully you will find the example useful.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<string>
#include<sstream>
#include<map>

using namespace std;

void split(const string& input, int& num1, int& num2, string& operation);
int calculate(int num1, int num2, string operation);

int main()
{
 string s[5] = {"2 + 2", "4 - 1", "4 * 6", "18 / 3", "12 ^ 2"};

 for(int i = 0; i < 5 ; i++)
 {
   int num1=0, num2=0;
   string op;
   split(s[i], num1, num2, op);
   int retVal = calculate(num1, num2, op);
   cout<<s[i]<<" = "<<retVal<<endl;
 }

 return 0;
}

void split(const string& input, int& num1, int& num2, string& operation)
{
 istringstream iss(input);
 iss >> num1;
 iss >> operation;
 iss >> num2;
}

int calculate(int num1, int num2, string operation)
{
 enum Operators {unknown, add, sub, mul, div};
 map<string, Operators> mapOfOperators;
 mapOfOperators["+"] = add;
 mapOfOperators["-"] = sub;
 mapOfOperators["*"] = mul;
 mapOfOperators["/"] = div;

 switch(mapOfOperators[operation])
 {
 case add:
   return num1 + num2;
 case sub:
   return num1 - num2;
 case mul:
   return num1 * num2;
 case div:
   return num1 / num2;
 default:
   cout<<"Unrecognised Operator "<<operation<<endl;
 }
 return 0;
}

The output is as follows:

See Also: Codeguru article on 'Switch on Strings in C++'.

Client/Server communication via sockets

The following is a simple Client Server example that actually covers quite a few different topics. The code is modified from the MadWizard.org Winsock Tutorial. It may be a good idea to go through the StringStreams example here and C/C++ String differences example here.

Please note that the code below is not the best example of coding practice.

Server code:

//Original Client-Server code from www.MadWizard.org
//Part of the Winsock networking tutorial by Thomas Bleeker
//Modified and tested on Microsoft Visual Studio 2008 - Zahid Ghadialy

#include <iostream>
#include <string>
#include <sstream>

#define WIN32_MEAN_AND_LEAN
#include <winsock2.h>
#include <windows.h>

//Add ws2_32.lib in Properties->Linker->Input->Additional Dependencies

using namespace std;

const int  REQ_WINSOCK_VER   = 2; // Minimum winsock version required
const int  DEFAULT_PORT      = 4444; 
const int  TEMP_BUFFER_SIZE  = 128;

//Forward Declarations
bool RunServer(int portNumber);

//MAIN
int main()
{ 
 int iRet = 1;
 WSADATA wsaData;

  cout << "SERVER STARTED" << endl;
 cout << "Initializing winsock... ";

 if (WSAStartup(MAKEWORD(REQ_WINSOCK_VER,0), &wsaData)==0)
 {
  // Check if major version is at least REQ_WINSOCK_VER
  if (LOBYTE(wsaData.wVersion) >= REQ_WINSOCK_VER)
  {
   cout << "initialized.\n";
   
   int port = DEFAULT_PORT;
   iRet = !RunServer(port);
  }
  else
  {
   cerr << "required version not supported!";
  }

  cout << "Cleaning up winsock... ";

  // Cleanup winsock
  if (WSACleanup()!=0)
  {
   cerr << "cleanup failed!\n";
   iRet = 1;
  }   
  cout << "done.\n";
 }
 else
 {
  cerr << "startup failed!\n";
 }
 return iRet;
}


string GetHostDescription(const sockaddr_in &sockAddr)
{
 ostringstream stream;
 stream << inet_ntoa(sockAddr.sin_addr) << ":" << ntohs(sockAddr.sin_port);
 return stream.str();
}

void SetServerSockAddr(sockaddr_in *pSockAddr, int portNumber)
{
 // Set family, port and find IP
 pSockAddr->sin_family = AF_INET;
 pSockAddr->sin_port = htons(portNumber);
 pSockAddr->sin_addr.S_un.S_addr = INADDR_ANY;
}

void HandleConnection(SOCKET hClientSocket, const sockaddr_in &sockAddr)
{
 // Print description (IP:port) of connected client
 cout << "Connected with " << GetHostDescription(sockAddr) << ".\n";
  exception e;

 char tempBuffer[TEMP_BUFFER_SIZE];

 // Read data
 while(true)
 {
  int retval;
  retval = recv(hClientSocket, tempBuffer, sizeof(tempBuffer), 0);
  if (retval==0)
  { 
   break; // Connection has been closed
  }
  else if (retval==SOCKET_ERROR)
  {
   exception e("socket error while receiving.");
      throw e;
  }
  else
  {
      string tempBufferString(tempBuffer);
      cout<<"Received over the socket :"<<tempBufferString<<endl;
      string tempString = "Loopbacked: " + tempBufferString + '\0';
      strcpy_s(tempBuffer, tempString.length() + 1, tempString.c_str());
   if (send(hClientSocket, tempBuffer, strlen(tempBuffer)+1, 0)==SOCKET_ERROR)
    {
     exception e("socket error while sending.");
        throw e;
    }
  }
 }
 cout << "Connection closed.\n";
}

bool RunServer(int portNumber)
{
 SOCKET hSocket = INVALID_SOCKET, hClientSocket = INVALID_SOCKET;
 bool bSuccess = true;
 sockaddr_in sockAddr = {0};
 
 try
 {
  // Create socket
  cout << "Creating socket... ";
  if ((hSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
    {
      cout << "failed Creating socket... \n";
      return false;
    }
  cout << "created.\n";
  
  // Bind socket
  cout << "Binding socket... ";
  SetServerSockAddr(&sockAddr, portNumber);
  if (bind(hSocket, reinterpret_cast<sockaddr*>(&sockAddr), sizeof(sockAddr))!=0)
    {
      cout << "failed Binding socket... \n";
      return false;
    }
  cout << "bound.\n";

  // Put socket in listening mode
  cout << "Putting socket in listening mode... ";
  if (listen(hSocket, SOMAXCONN)!=0)
    {
      cout << "failed Putting socket in listening mode... \n";
      return false;
    }
  cout << "done.\n";

  // Wait for connection
  cout << "Waiting for incoming connection... ";
  
  sockaddr_in clientSockAddr;
  int clientSockSize = sizeof(clientSockAddr);
  
  // Accept connection:
  hClientSocket = accept(hSocket,
       reinterpret_cast<sockaddr*>(&clientSockAddr),
       &clientSockSize);
 
  // Check if accept succeeded
  if (hClientSocket==INVALID_SOCKET)
    {
      cout << "accept function failed... \n";
      return false;
    }
  cout << "accepted.\n";
 
  // Wait for and accept a connection:
  HandleConnection(hClientSocket, clientSockAddr);

 }
 catch(exception& e)
 {
  cerr << "\nError: " << e.what() << endl;
  bSuccess = false; 
 }

 if (hSocket!=INVALID_SOCKET)
  closesocket(hSocket);
 
 if (hClientSocket!=INVALID_SOCKET)
  closesocket(hClientSocket);
  
 return bSuccess;
} 

Client code:

//Original Client-Server code from www.MadWizard.org
//Part of the Winsock networking tutorial by Thomas Bleeker
//Modified and tested on Microsoft Visual Studio 2008 - Zahid Ghadialy

#include <iostream>
#include <sstream>

#define WIN32_MEAN_AND_LEAN
#include <winsock2.h>
#include <windows.h>

using namespace std;

//Add ws2_32.lib in Properties->Linker->Input->Additional Dependencies

using namespace std;

const int  REQ_WINSOCK_VER   = 2; // Minimum winsock version required
const char DEF_SERVER_NAME[] = "127.0.0.1"; //localhost - can be your server name like "www.google.com"
const int  SERVER_PORT       = 4444; 
const int  TEMP_BUFFER_SIZE  = 128;

// IP number typedef for IPv4
typedef unsigned long IPNumber;

//Forward Declarations
bool RunClient(const char *pServername);

//MAIN
int main(int argc, char* argv[])
{
 int iRet = 1;
 WSADATA wsaData;

  cout << "CLIENT STARTED" << endl;
 cout << "Initializing winsock... ";

 if (WSAStartup(MAKEWORD(REQ_WINSOCK_VER,0), &wsaData)==0)
 {
  // Check if major version is at least REQ_WINSOCK_VER
  if (LOBYTE(wsaData.wVersion) >= REQ_WINSOCK_VER)
  {
   cout << "initialized.\n";
   
   // Set default hostname:
   const char *pHostname = DEF_SERVER_NAME;
   iRet = !RunClient(pHostname);
  }
  else
  {
   cerr << "required version not supported!";
  }

  cout << "Cleaning up winsock... ";

  // Cleanup winsock
  if (WSACleanup()!=0)
  {
   cerr << "cleanup failed!\n";
   iRet = 1;
  }   
  cout << "done.\n";
 }
 else
 {
  cerr << "startup failed!\n";
 }
 return iRet;
}


IPNumber FindHostIP(const char *pServerName)
{
 HOSTENT *pHostent;

 // Get hostent structure for hostname:
 if (!(pHostent = gethostbyname(pServerName)))
  {
    exception e("could not resolve hostname.");
    throw e;
  }
 
 // Extract primary IP address from hostent structure:
 if (pHostent->h_addr_list && pHostent->h_addr_list[0])
  return *reinterpret_cast<IPNumber*>(pHostent->h_addr_list[0]);
 
 return 0;
}

void FillSockAddr(sockaddr_in *pSockAddr, const char *pServerName, int portNumber)
{
 // Set family, port and find IP
 pSockAddr->sin_family = AF_INET;
 pSockAddr->sin_port = htons(portNumber);
 pSockAddr->sin_addr.S_un.S_addr = FindHostIP(pServerName);
}

bool RunClient(const char *pServername)
{
 SOCKET     hSocket = INVALID_SOCKET;
 char      tempBuffer[TEMP_BUFFER_SIZE];
 sockaddr_in sockAddr = {0};
 bool      bSuccess = true;
 
 try
 {
  // Lookup hostname and fill sockaddr_in structure:
  cout << "Looking up hostname " << pServername << "... ";
  FillSockAddr(&sockAddr, pServername, SERVER_PORT);
  cout << "found.\n";
 
  // Create socket
  cout << "Creating socket... ";
  if ((hSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
    {
      cout<<"could not create socket. "<<endl;
      return false;
    }
  cout << "created.\n";
  
  // Connect to server
  cout << "Attempting to connect to " << inet_ntoa(sockAddr.sin_addr)
       << ":" << SERVER_PORT <<  "... ";
  if (connect(hSocket, reinterpret_cast<sockaddr*>(&sockAddr), sizeof(sockAddr))!=0)
    {
      cout<<"could not connect. "<<endl;
      return false;
    }
  cout << "connected.\n";
  
  cout << "Sending requests and checking for loopbacks... "<<endl;

    //Lets sent 100 packets and get it looped back from Server
    for(int i = 0; i < 10; i++)
    {
      int retval = 0;
      stringstream ss (stringstream::in | stringstream::out);
      ss << "Message " << i <<"\n";

      std::string s = ss.str() + '\0'; //Adding the null charachter
      if (send(hSocket, s.c_str(), s.size() + 1, 0)==SOCKET_ERROR)
      {
        cout<<"failed to send data. "<<endl;
        return false;
      }

      retval = recv(hSocket, tempBuffer, sizeof(tempBuffer), 0);
      if (retval==0)
      {
        cout<<"Connection closed"<<endl;
        break;
      }
      else if (retval==SOCKET_ERROR)
      {
        exception e("socket error while receiving.");
        throw e;
      }
      else
      {
    // retval is number of bytes read
    // Terminate buffer with zero and print as string
    tempBuffer[retval] = 0;
        cout << "Received " << retval << " bytes. Received : " <<tempBuffer;
      }
    }  
 }
 catch(exception& e)
 {
  cerr << "\nError: " << e.what() << endl;
  bSuccess = false; 
 }

 if (hSocket!=INVALID_SOCKET)
 {
  closesocket(hSocket);
 }
 return bSuccess;
} 

The Server Output is as follows:

The Client output is as follows:

Example of Permutations in C++

Example of how you can let the Algorithm class generate permutations of String

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<algorithm>
#include<string>
#include<vector>

using namespace std;

int main()
{
  string someString="ABC";
  vector<string> someVector;

  someVector.push_back(someString);

  string::iterator itBegin = someString.begin();
  string::iterator itEnd = someString.end();

  while(next_permutation(itBegin, itEnd)) //std::next_permutation defined in algorithm
  {
    someVector.push_back(string(itBegin, itEnd));
  }
  copy(someVector.begin(), someVector.end(), ostream_iterator<string>(cout, "\n"));

  return 0;
}

The output is as follows:

Via: Learning C++: Permutations in C++

Example of Stringstreams

Here is an example of stringstream that I picked up from here and modified it slightly.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Simple example of C++ stringstreams

#include<iostream>
#include<sstream>
#include<string>

using namespace std;

int main()
{
  string input;

  cout<< "Please enter some numbers speretaed by space and press enter once done: ";
  getline(cin, input);

  cout<< "input = " << input << endl;

  stringstream memString(input, ios_base::in); //stringstream( string s, openmode mode )

  cout<<"memString = " << memString << endl;
  cout<<"memString (contents) = " << memString.str() << endl;

  double summ = 0; 
  double temp;
  while (memString >> temp)
  { 
    summ+= temp;
  }

  cout<<"summ = " << summ << endl;

  return 0;
}

The output is as follows:


See Also:
C++ Reference on stringstreams
Using Stringstreams in C++
String Stream example
String Streams Constructors