How to Retrieve the data from text file using VC++ Win32

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In Win32, Dynamically I have created the empty file & i had written some data to the newly created file. The code is like this:

C++

HANDLE hFile = CreateFile("E:\\pszFileName.txt", GENERIC_READ|GENERIC_WRITE,0,0,OPEN_ALWAYS, 
                          FILE_ATTRIBUTE_NORMAL, 0);

if( hFile != INVALID_HANDLE_VALUE)
{
    	char text[] = "This line was added\r\n";
    	DWORD dwBytesWritten = 0;
    	SetFilePointer(hFile, 0, 0, FILE_END);
    	WriteFile(hFile,text, strlen(text), &dwBytesWritten, 0);
    
    	CloseHandle(hFile);
}

Now the file pszFileName contains the data as "This line was added".

My question is : I want to Retrive the data from the file. Is there any way to get the data from the file ?

Posted 6-Mar-12 2:22am

Guru_C++

Updated 6-Mar-12 8:16am

Chris Maunder773K

v4

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6 solutions

Solution 1

If you already feel comfortable with WriteFile, ReadFile should be a cinch...
You may find that time spent in MSDN is time well invested.
Hope this helps,
Pablo.

Posted 6-Mar-12 2:25am

Pablo Aliskevicius

Comments

Guru_C++ 6-Mar-12 8:28am

I have used the ReadFile function, but actually it doesn't help me to retrieve the data .. Actually i need data from the File ...

Pablo Aliskevicius 6-Mar-12 8:41am

ReadFile will read the data in the file; you have to create CreateFile again, with different flags (GENERIC_READ only).
Try to play with the MSDN examples for ReadFile.
If what you want is data about the file (size on disk, date, ...) there are other API functions that may be of assistance.

See: http://msdn.microsoft.com/en-us/library/windows/desktop/aa365467(v=vs.85).aspx
and GetFileInformationByHandleEx (http://msdn.microsoft.com/en-us/library/windows/desktop/aa364953(v=vs.85).aspx)
Best wishes,
Pablo.

Solution 2

Use ReadFile() to get the data back. What is your problem?

Posted 6-Mar-12 2:34am

Richard MacCutchan

Solution 5

you can use fstream class available in standard template library (std) to read and write to files instead of the more complex win32 functions.I have used it before to create my on file system for my programs.

You can write to file as shown below

C++

#include <fstream>

using namespace std;

void main()
{

 string text = "This line was added\r\n"; //would rather use string than array

 ofstream out("E:\\pszFileName.txt",ios::out); //create and open file

 out>>text; //write to file

 out.close(); //close file

 return;
}

and you can read from file

C++

#include <fstream>

#include <iostream>

using namespace std;

void main()
{

 string text,str;

 ifstream in("E:\\pszFileName.txt"); //open existing file

 if(!in) return; //check if file actual exists return otherwise

  while(in)
  {
     in>>str; // read from file. NOTE: Here reading ignores the whitespaces
              
     if(in.eof()) break; //check if end of file is reached

     text += str + " "; // concatenate strings
  } 

 cout<<text; //write to console to check results

 in.close(); //close file

 return;
}

This is simpler and saves you from the complicated win32 functions.

Posted 6-Mar-12 12:12pm

BupeChombaDerrick

Updated 6-Mar-12 12:17pm

v2

Solution 6

If you want to use the average c++ style file I/O, try this link [^]and read away! :-)

Posted 6-Mar-12 16:38pm

DrBones69

Solution 3

I guess that you added that for test issue. Anyway if you wanna create an empty file just use the TRUNCATE_EXISTING mode: look here

http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858%28v=vs.85%29.aspx[^]

Posted 6-Mar-12 3:43am

Schehaider_Aymen

Updated 6-Mar-12 3:44am

v2

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Chandrakantt · Accepted Answer · 2012-03-06T06:05:00

Below provided code writes data and reads data from a text file. Have a look on it.

int _tmain(int argc, _TCHAR* argv[])
{
	HANDLE hFile = CreateFile("E:\\pszFileName.txt", GENERIC_READ|GENERIC_WRITE,0,0,OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);
	if( hFile != INVALID_HANDLE_VALUE)
	{
	   char text[] = "This line was added\r\n";
	   DWORD dwBytesWritten = 0;
	   SetFilePointer(hFile, 0, 0, FILE_END);
	   WriteFile(hFile,text, strlen(text), &dwBytesWritten, 0);

	   CloseHandle(hFile);
	}

	// Now Read the Data
	hFile = NULL;
	hFile = CreateFile("E:\\pszFileName.txt", GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);

	if( hFile != INVALID_HANDLE_VALUE)
	{
		char textOut[1024] = {0};
	   DWORD dwBytesRead = 0;
	   SetFilePointer(hFile, 0, 0, FILE_BEGIN);
	   ReadFile(hFile,textOut, 1024, &dwBytesRead, 0);
		MessageBox(NULL,textOut,"",MB_OK);
	   CloseHandle(hFile);
	}
	return 0;
}