Templates revisited: Best coding practice

[mythescriptid]

Hi All,
I know templates and STL might have been discussed many a times here, I'm bit of newbie as far as templates are concerned and was itching to test my new found linking of templates. I would like to continue discussing pro/cons and best methods of template implementation.

As a start I'm posting two simple template classes I have written for your review and let me know how can they be further improved and do they follow standard STL?

Feel free to post some good/innovative Template code you might have written ( as long as it does not infringe copyright ;-) )

Thanks in advance.
Hari.


*** CODE listing ***

/* Template class to join to strings 
I used templates since it will allow us to join any datatypes ( unless user defined!). 
I have written two versions of same functionality 
1. uses template class 
2. using static template function 
which approach is better and more generic?
 
*/
 
#if !defined mystrcat_HPP
#define mystrcat_HPP
 
#include <iostream>
#include <sstream>
#include <fstream>
#include <time.h>
 
using namespace std;
 
/* My Exception class  to handle if failed to join strings*/
 
class StrCatException { 
private: 
    std::string mFailedMsg;
public: 
     StrCatException(std::string failedReason){
          mFailedMsg="StrCatException: "+failedReason;
 
       }
      void printStackTrace()
      {
          cout <<mFailedMsg<<endl;
      }
};
 
 
/*
 * Template Class used for joining any two strings( any data type)
 */
 
template <class T,class S > 
class mystrcat 
{ 
    private:
        T mFirstString;
        S mSecondString;
        //mystrcat(){} // don't allow any default construction. Can't join without any param's right?
    public:
        mystrcat( T aFirstString ,S aSecondString) 
          {
              mFirstString=aFirstString;
              mSecondString =aSecondString;
          }
 
        std::string join()
        {
            time_t currTime;
            time(&currTime);
 
            std::stringstream _time2sString;
            _time2sString<<currTime;
 
            string _sString2String;
            _time2sString>>_sString2String;
 
            string fileName ="./strconv";
            fileName +=_sString2String;// forming a unique name
 
            ofstream ofs (fileName.c_str());
            if(!ofs) { throw StrCatException("Unable to open File for writing"); }
            ofs<<mFirstString<<mSecondString;
            ofs.close();
            ifstream ifs(fileName.c_str());
            if(!ifs) { throw StrCatException("Unable to open File for reading"); }
            std::string finalString;
            while(!ifs.eof())
            {
                std::string cline;
                getline(ifs,cline);
                finalString += cline;
            }
            remove(fileName.c_str());
            return finalString;
        }
 
};
 
#endif
 

***** end mystrcat.hpp ****

*** test class ***

#include "mystrcat.hpp"
int main()
{
 
try{
         mystrcat<std::string,int> cCatStrs("Hello How are :",10);
         std::string jS= cCatStrs.join();
         cout<<"Value is : "<<jS<<endl;
         cout<<"Value is : "<<mystrcat<std::string,std::string>(" second call "," Friday ").join()<<endl;
         cout<<"Value is : "<<mystrcat<std::string,double>(" double call ",5645.3434).join()<<endl;
         cout<<"Value is : "<<mystrcat<int,double>(1,45.3434).join()<<endl;
     }
     catch (StrCatException sce)
     {
        sce.printStackTrace();
        exit(-1);
     }
     catch (...)
     {
            cout<<"Failed to "<<endl;
            exit(-2);
     }
 
}

[mythescriptid]

*** Second version *****

#if !defined STRINGCAT_HPP
#define STRINGCAT_HPP
 
#include <iostream>
#include <sstream>
#include <fstream>
#include <time.h>
 
using namespace std;
 
/* My Exception class  to handle if failed to join strings*/
 
class CatException { 
private: 
    std::string mFailedMsg;
public: 
     CatException(std::string failedReason){
          mFailedMsg=failedReason;
 
       }
      void printStackTrace()
      {
          cout <<"CatException:"<<mFailedMsg<<endl;
      }
};
 
 
/*
 * Template Class used for joining any two strings( any data type)
 */
 
class StringCat 
{ 
 
    private:
        StringCat( )
          {
          }
 
    public:
        template <class T,class S> static std::string join(T mFirstString ,S mSecondString)
        {
            time_t currTime;
            time(&currTime);
 
            std::stringstream _time2sString;
            _time2sString<<currTime;
 
            string _sString2String;
            _time2sString>>_sString2String;
 
            string fileName ="/tmp/strconv";
            fileName +=_sString2String;// forming a unique name
 
            ofstream ofs (fileName.c_str());
            if(!ofs) throw CatException("Unable to open File for writing");
            ofs<<mFirstString<<mSecondString;
            ofs.close();
 
            ifstream ifs(fileName.c_str());
            if(!ifs) throw CatException("Unable to open File for reading"); 
            std::string finalString;
            while(!ifs.eof())
            {
                std::string cline;
                getline(ifs,cline);
                finalString += cline;
            }
 
            remove(fileName.c_str());
            return finalString;
        }
 
};
 
#endif

**** End of StringCat.hpp ****

#include "StringCat.hpp"
 
int main()
{
  cout <<StringCat::join("Hello", " Hi")<<endl;
  cout <<StringCat::join(10, " Hi")<<endl;
  cout <<StringCat::join(.01212, .2323)<<endl;
  cout <<StringCat::join(10, 11)<<endl;
  cout <<StringCat::join("Hello", 1231)<<endl;
 
}

[weaknessforcats]

What are you trying to do? Recreate the STL??

You concatenate strings in the STL by:

string str("Hello");
         str += "World";
 

You append strings by:

string str("Hello");
string str1("World");
string str2;
 
         str2 = str + str1;
 

[mythescriptid]

What are you trying to do? Recreate the STL??
Not Really :-)
You concatenate strings in the STL by:

string str("Hello");
         str += "World";
 

You append strings by:

string str("Hello");
string str1("World");
string str2;
 
         str2 = str + str1;
 

I know strings can be joined , actually I was writing some code where I need to join a String and a Int. And std::string does not allow that. So I wrote my own join method which can join two different data types ( like string + int, string+float etc ).

[weaknessforcats]

The STL solution is a different approach. Check this out:

//Concatenate a string and an int into a string
stringstream ss;
string str("The magic number is: ");
int data  = 123;
ss << str << data;
string result;
string token;
  while (!ss.eof())
  {
     ss >> token;
     result += token;
     result += ' ';
  }
cout << result << endl;
 

Here a stringstream is used and you just insert your data into the stream. Everything is converted to char since all of the templates are specialzed on char (or wchar_t but's that a different story). Then you just use the extractor of the stream to fetch the tokens. You build the result by appending the token and a space.

The type of code you are trying to get working is a duplication of STL features.

[mythescriptid]

The STL solution is a different approach. Check this out:

//Concatenate a string and an int into a string
stringstream ss;
string str("The magic number is: ");
int data  = 123;
ss << str << data;
string result;
string token;
  while (!ss.eof())
  {
     ss >> token;
     result += token;
     result += ' ';
  }
cout << result << endl;
 

Here a stringstream is used and you just insert your data into the stream. Everything is converted to char since all of the templates are specialzed on char (or wchar_t but's that a different story). Then you just use the extractor of the stream to fetch the tokens. You build the result by appending the token and a space.

The type of code you are trying to get working is a duplication of STL features.

agree stringstream does allow us to use "<<" operator to write(append) and read back into string. But I find it to be confusing and it eats up the spaces in a string for example:
if str = " Hello here are _sp_ _sp_ _sp_ many spaces in ";// _sp_ to represent a single white space
even if I use your logic ( as above ) would still lose the multiple spaces.