How do I open an existing file so new data is appended in Visual Studion2010 C++

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With the code listed below, new data overwrites the existing data. I want to append the new data to that already in the file

hFile = CreateFile ((LPCTSTR) szSaveName, GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_APPEND_DATA , NULL) ;
bSuccess=WriteFile(hFile,sData,num,&written,NULL);

Regards,Roland

Posted 23-Jun-14 4:21am

Sir Roland

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Comments

[no name] 23-Jun-14 10:28am

http://msdn.microsoft.com/en-us/library/windows/desktop/aa363778(v=vs.85).aspx

Sergey Alexandrovich Kryukov 23-Jun-14 11:56am

Visual Studio is just the IDE. It does not open files of your applications and does not even build them... :-)
—SA

Sir Roland 23-Jun-14 12:28pm

Yes, that's true. Perhaps you didn't notice. I'm referring to Visual Studio C++.

Sergey Alexandrovich Kryukov 23-Jun-14 13:15pm

I noticed that...
—SA

3 solutions

Solution 2

Take a look at MSDN: CreateFile function.

The documentation says that the FILE_APPEND_DATA should go into the second parameter (dwDesiredAccess) and that FILE_WRITE_DATA should not be set in this case.

Have you tried that? Otherwise, I would go with the KarstenK's solution.

Posted 23-Jun-14 10:23am

nv3

Comments

Sir Roland 25-Jun-14 22:02pm

Thanks for the solution. I read the documentation, apparently not closely enough
regards, Roland

Solution 3

Why not just use the (portable) STL? Just create an fstream with read and write permissions (which is the default), move the write-cursor to the end of the buffer and start writing. A demonstrating example:

C++

#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;

int main()
{
    fstream file("somefile");
    file.seekp(0, ios_base::end);

    file << "\nadditional stuff";
}

Posted 24-Jun-14 11:31am

Joren Heit

Updated 24-Jun-14 11:33am

v2

Comments

Sir Roland 25-Jun-14 22:04pm

Thanks for the suggestion. I'll probably go with Solution 2.

Joren Heit 30-Jun-14 7:53am

Sure, always go with the non-portable solution.

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KarstenK · Accepted Answer · 2014-06-23T06:31:00

Solution 1

you need the function SetFilePointer
Here is a sample code from MS.

Posted 23-Jun-14 6:31am

KarstenK

Comments

CPallini 23-Jun-14 12:33pm

5.

Joren Heit 24-Jun-14 17:33pm

Non-portable! Why not use STL when you can? See my answer :-)