A Class for Creating a Trace Log

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Introduction

So the Debug build works great, but the Release build crashes? Or the program works fine on your computer, but crashes on the customer's computers? You need to add trace functionality to the Release build.

CLogTrace is a class that allows you to easily add trace functionality to the release build of a program. You make the program write lines of text to a log file at various stages in the program. You provide the code to turn the logging on or off. Much like using the TRACE macro, you get a text file that tells you what functions were called, with a date/time stamp. Except you can get this information in release builds.

The class is easy to use.

1. Make a static CLogTrace object as a member of the application class.
2. Add the initialization lines in the program's InitInstance function.
3. Any time you want to write to the log file, use the CLogTrace::WriteLine functions - these will write the text along with date and time.

Here is an example log file output:

11/4/99 10:16:44 PM	Started the application
11/4/99 10:16:44 PM	Created doc template
11/4/99 10:16:44 PM	CDoc constructor
11/4/99 10:16:44 PM	Precreate window
11/4/99 10:16:44 PM	Precreate window
11/4/99 10:16:44 PM	CView Constructor
11/4/99 10:16:44 PM	CView::Precreate window
11/4/99 10:16:44 PM	Created main window
11/4/99 10:16:44 PM	Created tool bar
11/4/99 10:16:44 PM	Created status bar
11/4/99 10:16:44 PM	OnNew Document
11/4/99 10:16:44 PM	Leaving InitInstance
11/4/99 10:16:46 PM	Leaving the application

Here is the class interface:

////////////////////////////////////////////////////////////////////////
//  LogTrace.cpp -- Interface for the CLogTrace class
//  A class to do debug logging

#ifndef __LOGTRACE_H__
#define __LOGTRACE_H__

class CLogTrace
{
// Construction/Destruction
public:
	CLogTrace();
	~CLogTrace();

// Attributes
public:
	CString m_strAppName;

protected:
	BOOL m_bActive;
	CString m_strFileName;
	BOOL m_bTimeStamp;

// Operations
public:
	void WriteLine(LPCTSTR szLine);
	void WriteLine(LPCTSTR szFormat, LPCTSTR szAddInfo);
	void WriteLine(LPCTSTR szFormat, int nAddInfo);
	void ResetFile();
	void OnStartup(BOOL bActive, BOOL bTimeStamp);
	void SetFileName(LPCTSTR szFileName);

protected:

// Inlines
public:
	inline void SetActive(BOOL bSet)
	{
		m_bActive = bSet;
	}
	inline CString GetFileName()
	{
		return m_strFileName;
	}
};

#endif // __LOGTRACE_H__

Here is the class implementation:

////////////////////////////////////////////////////////////////////////
//  LogTrace.cpp -- Implementation of the CLogTrace class

#include "stdafx.h"
#include "LogTrace.h"

/**************************************************

 How to use CLogTrace

	1.  Make a static CLogTrace object as a member of the application class
	2.	Add the following lines to the InitInstance of the program
	
	m_LogTrace.m_strAppName = "MyApp"; // use appropriate name here
	m_LogTrace.SetFileName("Log.txt"); // sets the log file name and puts it in the exe path
	m_LogTrace.OnStartup(TRUE, TRUE); // activates the log trace

	3.  Also in InitInstance, add the following line if you want to empty the log file
	each time the application starts
	m_LogTrace.ResetFile();

	4.  Any time you want to write to the log file, use the CLogTrace::WriteLine functions
	these will write the text along with date and time

*******************************************************/

//////////////////////////////////////////////////////
//  Construction/Destruction

CLogTrace::CLogTrace()
{
	m_bActive = FALSE;
	m_bTimeStamp = TRUE;

	CString s;
}

CLogTrace::~CLogTrace()
{

}

////////////////////////////////////////////////////////
//  CLogTrace operations

void CLogTrace::ResetFile()
{
	CStdioFile f;
	CFileException fe;
	CString s;

	if (m_strFileName.IsEmpty()) return;

	if (f.Open(m_strFileName, CFile::modeWrite | CFile::modeCreate, &fe) == FALSE)
	{
		return;
	}

	f.Close();
}

// bActive tells us if we want the trace to be active or not
// bTimeStamp tells us if we want time stamps on each line
// eliminating the time stamp allows us to use this class for a regular log file
void CLogTrace::OnStartup(BOOL bActive, BOOL bTimeStamp)
{
	m_bActive = bActive;
	m_bTimeStamp = bTimeStamp;
	if (bTimeStamp == FALSE) return;
	CString s;

	// these ***'s help to indicate when one ru of the program ends and another starts
	// because we don't always overwrite the file each time

	WriteLine("\n\n******************************************\n\n");
	s.Format("%s Log Trace %s\n\n", m_strAppName, COleDateTime::GetCurrentTime().Format());
	WriteLine(s);
}

// function to write a line of text to the log file
void CLogTrace::WriteLine(LPCTSTR szLine)
{
	CStdioFile f;
	CFileException fe;
	CString s;

	if (m_bActive == FALSE) return;
	if (m_strFileName.IsEmpty()) return;

	if (f.Open(m_strFileName, CFile::modeWrite | CFile::modeCreate |
		CFile::modeNoTruncate, &fe) == FALSE)
	{
		return;
	}

	try
	{
		f.SeekToEnd();
		TRACE("LOGGIN %s\n", szLine);
		if (m_bTimeStamp)
		{
			s.Format("%s\t%s\n", COleDateTime::GetCurrentTime().Format(),
				szLine);
		}
		else
		{
			s.Format("%s\n", szLine);
		}
		f.WriteString(s);
	}
	catch (CException* e)
	{
		// Note that there is not much we can do if there is an exception
		// It is not practical to tell the user each time
		// and we can't write the error to a log file!!!!
		e->Delete();
	}
	f.Close();
}

// function to write a line of text, with an extra string
void CLogTrace::WriteLine(LPCTSTR szFormat, LPCTSTR szAddInfo)
{
	if (m_bActive == FALSE) return;
	CString s;
	s.Format(szFormat, szAddInfo);
	WriteLine(s);
}

// function to write a line of text with an extra integer
void CLogTrace::WriteLine(LPCTSTR szFormat, int nAddInfo)
{
	if (m_bActive == FALSE) return;
	CString s;
	s.Format(szFormat, nAddInfo);
	WriteLine(s);
}

// function to set the log file name.  don't pass a fill path!
// just pass something like "log.txt"
// the file will be placed in the same dir as the exe file
void CLogTrace::SetFileName(LPCTSTR szFileName)
{
	TCHAR drive[_MAX_PATH], dir[_MAX_PATH], name[_MAX_PATH], ext[_MAX_PATH];
	const char *path = _pgmptr ;
	_splitpath(path, drive, dir, name, ext);
	m_strFileName.Format("%s%s%s", drive, dir, szFileName);
}

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