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How to create an enum and callback function

, 2 Apr 2005 CPOL
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This article describes how to declare an enum function

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Introduction

Have you ever seen functions by name EnumFunctions? Like EnumWindows etc. Have you ever wondered how they are created? In this article, we will create a simple one! Just be relaxed and read this article to EOF!

What is an enum function?

These types of functions are ...!?! Let me explain like this: assume that you have some fruits. OK? Some apples, oranges, and bananas. You are searching for apples. And, for each apple you can find, you will shout: "Hey I found another apple!" This is the role of this type of functions: for each element, return something.

Let's start

Declaring an EnumFunction is simple. First, you should have a variable type to tell the function what kind of function is the input. See this code snippet (declarations in the header file):

typedef BOOL (CALLBACK*YOURPROCTYPE)(FirstType,SecondType,...);

Now see mine:

typedef BOOL (CALLBACK*MYPROC)(LPCTSTR);

And for declaring the EnumFunction:

ReturnType WINAPI EnumFunction(YOURPROCTYPE lpProcname,arg-list,…);

And mine:

BOOL WINAPI EnumFunc(MYPROC lpProc);

EnumFunc passes the parameters to a callback function:

ReturnType CALLBACK yourProcName(FirstType,SecondType,...);

Note that the argument list of this callback function must be what you give in YOURPROCTYPE:

BOOL CALLBACK MyProc (LPCTSTR prompt);

Here are my sample code declarations:

typedef BOOL (CALLBACK*FILESPROC)(LPCTSTR);
void WINAPI EnumFiles(FILESPROC lpEnumFiles,LPCTSTR lpszFileName);
int CALLBACK EnumFilesProc (LPCTSTR lpszFileName);

And here goes the EnumFiles function. Its task is to find the files in the given path, and for each file, calls the callback function:

void WINAPI EnumFiles(FILESPROC lpEnumFiles,LPCTSTR lpszFileName)
{
        CString nfle;
        numoffiles=0;
        CFileFind file;
        BOOL bFind=file.FindFile(lpszFileName,NULL);//Find first file in the given
        //path
        while (bFind)//While bFind==True continue finding...
        {
               bFind=file.FindNextFile(); //Find next file
               numoffiles=lpEnumFiles(file.GetFileName());//Call given callback function
               //by user with appropriate inputs 
        }
        nfle.Format("%d  Files found",numoffiles);
        AfxMessageBox(nfle);//Give the user number of files found in
        //the given path
}

BOOL CALLBACK EnumFilesProc(LPCTSTR lpszFileName)
{ 
        numoffiles++;
        list->InsertString(list->GetCount(),lpszFileName); 
        return numoffiles;
}

Now for calling the EunmFunction, you only need to write some code:

list->ResetContent();
EnumFiles(EnumFilesProc,"C:\\*.exe");

In this source code, we will get a path and enumerate all the files in the path! I use this enumeration technique to get all the sections in an INI file, and you can do anything you want! Any opinions and comments are welcome. Or questions maybe..

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

dSolariuM
Web Developer
United States United States
I started Visual C++ on 2003 and I am a beginner now,I am working on a Network program and I am searching for some partners.I am intrested in DLLs and GUI in programing.

Comments and Discussions

 
GeneralThank You! PinmemberAndy San23-May-06 2:20 
QuestionWhat? PinmemberSreekanth Muralidharan6-Dec-05 19:24 
AnswerRe: What? PinmemberThatsAlok6-Dec-05 21:46 
GeneralRe: What? PinmemberSreekanth Muralidharan8-Dec-05 16:51 
GeneralRe: What? PinmemberThatsAlok8-Dec-05 17:34 
GeneralRe: What? PinmemberSreekanth Muralidharan8-Dec-05 22:00 
GeneralRe: What? PinmemberSreekanth Muralidharan22-Nov-06 5:51 
GeneralRe: What? PinmemberThatsAlok23-Nov-06 0:09 
GeneralRe: What? PinmemberSreekanth Muralidharan24-Nov-06 5:22 
GeneralRe: What? Pinmemberoldkingcoleman21-Nov-06 7:51 

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