Extension to the STL "find_if" and "for_each"

The stl algorithms for_each and find_if are inadequate when you need more data for the predicate. Here are two new algorithms TDfind_if and TDfor_each which solve that problem.
To use:

std::list<OBJECT> theList;

class DATA
{
public:
    bool IsValid(const OBJECT& rObject) const;
    void OperateOn(OBJECT& rObject) const;
};

bool IsValid(OBJECT theObject, DATA theData)
{
    return theData.IsValid(theObject);
}

void DoOperation(OBJECT theObject, DATA theData)
{
    theData.OperateOn(theObject);
}

DATA theData;

OBJECT theObject = ::TDFind_if(theList.begin(), theList.end(), IsValid, theData);
or
::TDfor_each(theList.begin(), theList.end(), DoOperation, theData);

// CODE STARTS HERE:
/////////////////////////////////////////////////////////////////
// This is like the Standard c++ algorithm find_if, but it takes a second parameter
template<class _II, class _Pr, class T_DATA> inline 
_II
TDfind_if(
  _II _F, // First iterator
  _II _L, // Last iterator
  _Pr _P, // Predicate: a static function that returns bool having two
paramters
  T_DATA dwData)
{
    for (; _F != _L; ++_F)
    {
        if (_P(*_F, dwData))
        {
            break;
        }
    }

    return (_F);
}


template<class _II, class _Fn, class T_DATA> inline
void
TDfor_each(
  _II _F,
  _II _L,
  _Fn _Op,
  T_DATA dData)
{
    for (; _F != _L; ++_F)
    {
        _Op(*_F, dData);
    }
}

Date Posted: 5/4/98
Posted by: Pat Laplante.



Comments

  • mayyouhelpme

    Posted by Legacy on 11/03/2002 12:00am

    Originally posted by: tangsilai

    hello
    I am a new man in this aspect, And I want some comments of your how to use c++ freely.I am too sad to found it is to hard to learn.Help me please!!

    Reply
  • Even plainer STL

    Posted by Legacy on 08/13/1999 12:00am

    Originally posted by: Dana P'Simer

    The following code shows how to use just STL to implement
    
    the exact same functionality without the use of custom
    implementations of find_if and for_each, custom function
    objects, or custom adapter objects. It uses std::bind1st
    and std::mem_fun1 to call the memeber functions of DATA
    with the OBJECT as an argument.

    -----------------------
    #include <list>
    #include <algorithm>
    #include <iostream>

    typedef int OBJECT;

    std::list<OBJECT> theList;

    class DATA
    {
    public:
    bool IsValid(OBJECT rObject) { return rObject == 5; }
    int OperateOn(OBJECT rObject) { std::cout << rObject << std::endl; return 0; }
    };

    int main(int argc, char* argv[])
    {
    DATA theData;

    // fill the list
    for( OBJECT i = 0; i < 10; i++ )
    theList.push_back(i);

    // find the 5
    std::cout << "The results of find_if:" << std::endl;
    OBJECT theObject = *std::find_if(theList.begin(), theList.end(), std::bind1st(std::mem_fun1(DATA::IsValid),&theData) );
    std::cout << theObject << std::endl;

    // print the list
    std::cout << "The results of for_each:" << std::endl;
    std::for_each(theList.begin(), theList.end(), std::bind1st(std::mem_fun1(DATA::OperateOn),&theData));

    char c;
    std::cin >> c;
    return 0;
    }

    Reply
  • Plain STL

    Posted by Legacy on 10/27/1998 12:00am

    Originally posted by: Ithier de Lestrange

    You do not need to rewrite the find_if and for_each algorithms to have more arguments. You just need to use a
    struct (and the operator() function) as shown below:
    
    


    struct ex : public std::unary_function<OBJECT&, void>
    {
    ex (short Param1, bool Param2) :
    n_Param1(Param1), b_Param2 (Param2)
    {
    }
    void operator() (OBJECT& x)
    {
    x.Function1 (m_Param1, b_param2);
    }

    int n_Param1;
    bool b_Param2;
    };

    std::list<OBJECT> TheList;

    std::for_each (TheList.begin(), TheList.end(), ex(3, false));


    At http://www.sgi.com/Technology/STL/ you can find a very good documentation about STL.

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • With JRebel, developers get to see their code changes immediately, fine-tune their code with incremental changes, debug, explore and deploy their code with ease (both locally and remotely), and ultimately spend more time coding instead of waiting for the dreaded application redeploy to finish. Every time a developer tests a code change it takes minutes to build and deploy the application. JRebel keeps the app server running at all times, so testing is instantaneous and interactive.

  • Download the Information Governance Survey Benchmark Report to gain insights that can help you further establish business value in your Records and Information Management (RIM) program and across your entire organization. Discover how your peers in the industry are dealing with this evolving information lifecycle management environment and uncover key insights such as: 87% of organizations surveyed have a RIM program in place 8% measure compliance 64% cannot get employees to "let go" of information for …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds