C++ & MFC: Absurdal memory leaks... Why?

[NTxC]

Hello.
I'm currently having a memory leak problem in my program (C++ with MFC, VS2005) and I don't know WHY it happens, as the code seems to be OK to me. Anyway, here's the code that causes memory leaks:

char* va( char* FormatStr, ... )
{
	va_list ArgPtr;
	char *FinalString;
	int length;

	va_start( ArgPtr, FormatStr );

	length = _vscprintf( FormatStr, ArgPtr )+1;
	FinalString = new char[length];
	vsprintf_s( FinalString, length, FormatStr, ArgPtr );

	va_end( ArgPtr );
	return FinalString;
}

void CMFC1Dlg::OnBnClickedButton1()
{
	if( m_POpened )
	{
		CString cmd;
		m_EditCmd.GetWindowTextA( cmd );
		m_Port.WriteToPort( va( "%s%c", cmd, 13 ) );
	}
}

I have searched the forums already, but found no solution to this... These are the leaks (assuming cmd = "AT" ):

The thread 'Win32 Thread' (0x9a4) has exited with code 100 (0x64).
The thread 'Win32 Thread' (0x6b0) has exited with code 0 (0x0).
Detected memory leaks!
Dumping objects ->
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {140} normal block at 0x003B9ED0, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {112} normal block at 0x003B9BB8, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {110} normal block at 0x003B3828, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
Object dump complete.
The program '[2636] MFC1.exe: Native' has exited with code 0 (0x0).

Debugger points to FinalString = new char[length]; as the source of the leak. Could you please help me out?

Kind regards
Pat

[Ancient Dragon]

memory is allocated on line 10 but never deleted. Try this:

void CMFC1Dlg::OnBnClickedButton1()
{
        char *ptr;
	if( m_POpened )
	{
		CString cmd;
		m_EditCmd.GetWindowTextA( cmd );
                ptr = va( "%s%c", cmd, 13 );
		m_Port.WriteToPort( ptr);
                delete[] ptr;
	}
}

[tux4life]

Hello.
I'm currently having a memory leak problem in my program (C++ with MFC, VS2005) and I don't know WHY it happens, as the code seems to be OK to me. Anyway, here's the code that causes memory leaks:

char* va( char* FormatStr, ... )
{
	va_list ArgPtr;
	char *FinalString;
	int length;

	va_start( ArgPtr, FormatStr );

	length = _vscprintf( FormatStr, ArgPtr )+1;
	FinalString = new char[length];
	vsprintf_s( FinalString, length, FormatStr, ArgPtr );

	va_end( ArgPtr );
	return FinalString;
}

void CMFC1Dlg::OnBnClickedButton1()
{
	if( m_POpened )
	{
		CString cmd;
		m_EditCmd.GetWindowTextA( cmd );
		m_Port.WriteToPort( va( "%s%c", cmd, 13 ) );
	}
}

I have searched the forums already, but found no solution to this... These are the leaks (assuming cmd = "AT" ):

The thread 'Win32 Thread' (0x9a4) has exited with code 100 (0x64).
The thread 'Win32 Thread' (0x6b0) has exited with code 0 (0x0).
Detected memory leaks!
Dumping objects ->
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {140} normal block at 0x003B9ED0, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {112} normal block at 0x003B9BB8, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
e:\dawg\prg\vs2005\c++\mfc1\mfc1\mfc1\mfc1.cpp(102) : {110} normal block at 0x003B3828, 4 bytes long.
 Data: <AT  > 41 54 0D 00 
Object dump complete.
The program '[2636] MFC1.exe: Native' has exited with code 0 (0x0).

Debugger points to FinalString = new char[length]; as the source of the leak. Could you please help me out?

Kind regards
Pat

Yes, every time the 'va' function executes it allocates new memory, and returns a pointer to the newly allocated memory, but you don't delete the assigned memory when you don't need it anymore and that causes the memory leak :) ...

[NTxC]

Thank you very much! I forgot to free up the memory indeed.
But this way, I won't be able to use va() inline... I have to declare a pointer and delete it every time I want to use va(). Or is there some other way around, like freeing up the memory in va()?

[tux4life]

Or is there some other way around, like freeing up the memory in va()?

In the code you post this will lead to undefined behavior, as you're returning a pointer which points to deallocated memory, that's very dangerous :)

[NTxC]

Well, it looks like my dream of an inline variable argument function is gone...

Thank you for your help! :)

[Ancient Dragon]

you could do this:

void CMFC1Dlg::OnBnClickedButton1()
{
        char *ptr;
	if( m_POpened )
	{
		CString cmd;
		m_EditCmd.GetWindowTextA( cmd );
		m_Port.WriteToPort( (ptr = va( "%s%c", cmd, 13 )));
                delete[] ptr;
	}
}

or this:

const char* va( char* FormatStr, ... )
{
	va_list ArgPtr;
	static char FinalString[2048];
	va_start( ArgPtr, FormatStr );
	vsprintf_s( FinalString, sizeof(FinalString), FormatStr, ArgPtr );
	va_end( ArgPtr );
	return FinalString;
}

[NTxC]

or this:

const char* va( char* FormatStr, ... )
{
	va_list ArgPtr;
	static char FinalString[2048];
	va_start( ArgPtr, FormatStr );
	vsprintf_s( FinalString, sizeof(FinalString), FormatStr, ArgPtr );
	va_end( ArgPtr );
	return FinalString;
}

Sir, you are my saviour! Thank you very much, it's much better this way.

Thank you and have a good day! ;)