Logging Data

I've tried a lot of times to create a logging function (using \n to go to the next line), but with no luck. Here's my logging function:

PHP Code:

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#include <fstream.h>

char* szDataToLog(char* Data)
{
    ofstream fout;
    fout.open("log.txt");
    fout << Data << "\n";
    fout << flush;
    fout.close();
    return Data;
} 


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and here's how I use it:

PHP Code:

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szDataToLog("data\n"); 


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My problem is that when I do this, when I call it another time, it deletes "data" with the new text.

Anyone got any ideas on how to fix this?

It has something to do with the way your opening the file. Your opening it in write mode, but it should be opened in append mode. I think it should look something like this:

ofstream fout("log.txt", ios::append);

But I'm not sure if its ios::append or not, but give that a go. Its something like that anyway.

I believe it's ios::app. Also, use code tags, not PHP tags. Unless you're posting PHP code that is.

Try

Code:

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fout.open("log.txt", ios::app);

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Quote:

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Originally posted by XSquared
I believe it's ios::app. Also, use code tags, not PHP tags. Unless you're posting PHP code that is.

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That worked, thank you.

Sorry, I just like the cool coloring [heh].

[EDIT: Does anyone know why I can't view the class members? I'm using MSVC++ 6.0 Enterprise].

Ahh there we go, knew it was something like that.

Why don't you guys like code tags? Personally I think they are brilliant for any sort of code, simply because its coloured and so easier to follow. Don't you guys work with any sort of syntax highlighting? Or is that just for us non-pros out there :(

Quote:

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Originally posted by stovellp
Ahh there we go, knew it was something like that.

Why don't you guys like code tags? Personally I think they are brilliant for any sort of code, simply because its coloured and so easier to follow. Don't you guys work with any sort of syntax highlighting? Or is that just for us non-pros out there :(

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Code tags ain't colored, PHP tags are.

One more thing, is there a way to clear the file of data, and then write the stuff again?
(EX: Someone runs my program, it saves data. The person runs the program again, it clears the data, and then writes it again)

At the start of your program, just do this:

Code:

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fout.open( "log.txt" );
fout.close( );

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And it should clear it out.

io open_mode

ios::trunc - Deletes all previous content in the file

Quote:

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Originally posted by XSquared
At the start of your program, just do this:

Code:

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fout.open( "log.txt" );
fout.close( );

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And it should clear it out.

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Yup, that worked, thank you.

[EDIT]: ios::trunc deletes everything except the last line (I have about 4-6 lines to write at the moment to the file). Thanks though.

Ops, its late, when I said 'code' tags it should have read PHP tags. I'm going to make a thread about this in the general discussions forum tommorow to see what people think.

[EDIT]: Does anyone know how to get the last error from GetLastError and turn it into a string? :[/EDIT]

Does anyone know about the not being able to see class members?

[When I do

Code:

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ofstream fout;
fout.open("...");
.....
fout.close();

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VC++ won't display class members of fout, nor any other members.]

I looked at the docs on GetLastError(), and at the bottom in the "See also", it listed FormatMessage(). I'm not 100% sure that's what you're looking for, but it's probably worth looking into. Or, of course, you could do a switch :D

**EDIT**
Just so you know, you should be including <fstream> and not <fstream.h>, and then put "using namespace std;" at the top of your code file.

Quote:

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Originally posted by Hunter2
I looked at the docs on GetLastError(), and at the bottom in the "See also", it listed FormatMessage(). I'm not 100% sure that's what you're looking for, but it's probably worth looking into. Or, of course, you could do a switch :D

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Thank you, I'll look into that, and post to tell what happens.

Code:

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#include <windows.h>
#include <stdio.h>

void DisplayError( LPSTR msg, DWORD err )
{
        char msgbuf[4096];

        sprintf(msgbuf,"%s\nWindows Error %d: ",msg, err );

        FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM, NULL, err,
                MAKELANGID( LANG_NEUTRAL, SUBLANG_DEFAULT),
                msgbuf + lstrlen(msgbuf), sizeof( msgbuf ) - lstrlen(msgbuf), NULL );

        MessageBox(NULL,msgbuf,"Error",MB_ICONERROR);
}

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Quote:

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Originally posted by anonytmouse

Code:

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#include <windows.h>
#include <stdio.h>

void DisplayError( LPSTR msg, DWORD err )
{
        char msgbuf[4096];

        sprintf(msgbuf,"%s\nWindows Error %d: ",msg, err );

        FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM, NULL, err,
                MAKELANGID( LANG_NEUTRAL, SUBLANG_DEFAULT),
                msgbuf + lstrlen(msgbuf), sizeof( msgbuf ) - lstrlen(msgbuf), NULL );

        MessageBox(NULL,msgbuf,"Error",MB_ICONERROR);
}

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This didn't help me at all, I want to display the error as a string, not a #. Thanks though.

Hunter, I'll see what I can do with it.

Quote:

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This didn't help me at all, I want to display the error as a string, not a #. Thanks though.

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The supplied code will display the error message associated with the supplied error number.

Code:

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bRet = ReadFile(...);
if (!bRet) {
    DisplayError("Some Context.", GetLastError() );
}

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Sample output:
Some Context.
Windows Error 38: Reached the end of the file.

Alternatively you can write a thousand plus switch case with the error messages and numbers found here:
http://msdn.microsoft.com/library/en...rror_codes.asp

Please consider actually trying the code.

Have Fun!

Quote:

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Originally posted by anonytmouse
The supplied code will display the error message associated with the supplied error number.

Code:

---

bRet = ReadFile(...);
if (!bRet) {
    DisplayError("Some Context.", GetLastError() );
}

---

Sample output:
Some Context.
Windows Error 38: Reached the end of the file.

Alternatively you can write a thousand plus switch case with the error messages and numbers found here:
http://msdn.microsoft.com/library/en...rror_codes.asp

Please consider actually trying the code.

Have Fun!

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I did try the code....I got something like that working anyhow, thanks though.