Problem with pointers memory allocation on the same memory area - C / C++ / MFC Discussion Boards

Re: Reading a text file from a remote machine in LAN using c, c++, vc++

CPallini28-May-20 10:08

CPallini

28-May-20 10:08

Nice.

Get expanded macros from precompiler and insert as comments in source code?

arnold_w27-May-20 20:14

arnold_w

27-May-20 20:14

I am working with embedded C and sometimes I compile with Eclipse/GCC and sometimes with STMicroelectronics System Workbench. In my code there are a lot of nested macros and I think it would be great to display the expanded macro value as a comment right after the macro (note: only the macros without parameters). So I was thinking of having a post-build .exe-file/script that takes the result from the precompiler and puts it back into the source code as comments after the macros. As an alternative, I could have a pre-build .exe-file/script that executes the pre-compiler (meaning it will be executed twice for each compile) and then modifies the source code. I feel fairly confident about writing the .exe-file/script, but I have no idea how to execute the precompiler "on demand" or how to view the results of it. Could someone please provide some guidelines on how to achieve this? I know pretty much nothing about makefiles, precompilers, compilers, etc, so please feel free to formulate your answers in this thread in the way you would communicate with a beginner programmer.

Re: Get expanded macros from precompiler and insert as comments in source code?

Richard MacCutchan27-May-20 22:44

Richard MacCutchan

27-May-20 22:44

See Overall Options (Using the GNU Compiler Collection (GCC))[^]. The -E option of gcc allows you to stop the build after running the preprocessor. The out put will be the expanded source. But be aware that this will include the expansions of all input from included headers so may well be quite extensive. If you run a few samples you should be able to see how to get to the source that you are interested in.

Re: Get expanded macros from precompiler and insert as comments in source code?

arnold_w27-May-20 23:23

arnold_w

27-May-20 23:23

I just tried it, but it seems I need to reference the macros in order to get the expanded values. Most of my macros are never referenced in the project I would like to generate the explanatory comments in, they are just defined in a (shared) .h-file.

Re: Get expanded macros from precompiler and insert as comments in source code?

Richard MacCutchan27-May-20 23:34

Richard MacCutchan

27-May-20 23:34

If they are not used then the preprocessor will ignore them. Macro expansion happens at the reference, not at the definition. You may need to create some dummy file to get the expansions. A better idea would be to write proper documentation comments so they can be seen by anyone looking at the definitions. And I think that may also make them visible through intellisense.

How to mount an ISO file with disc type - CD/DVD

Member 1001484126-May-20 5:04

Member 10014841

26-May-20 5:04

I am creating an application using c# winform to create and mount ISO files like wincdemu. I am able to create the ISO file and mount it like a local drive. I want to mount the image with disc type CD-ROM/DVD-ROM. I am using AttachVirtualDisk() to mount the image.

Is there any API/library support to mount the image with disc type CD-ROM/CD-R/CD-RW/DVD-ROM/DVD-RAM etc. ?

I appreciate any advice.

Re: How to mount an ISO file with disc type - CD/DVD

jeron126-May-20 5:21

jeron1

26-May-20 5:21

You might be better off asking in the C# forum.

"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
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Problem with pointers memory allocation on the same memory area

Member 959508024-May-20 20:37

Member 9595080

24-May-20 20:37

Hello,

We use a third party library for our grids. Each grid cell has a style, one member of which is the font:

C++

class CLibStyle
{
	[...]
	CLibFont m_pFont;
	[...]
};

During deserialization ~~serialization~~ in the library methods, the font is managed as follows:

C++

ar >> m_pFont;

For our part, we deserialize the styles line by line, column by column, then storing them in a map to use them later:

C++

CLibStyle * pStyle = NULL;
for (int nNumRow = 0; nNumRow ++; nNumRow <nNbRow)
	for (int nNumCol = 0; nNumCol ++; nNumCol <nNbCol)
	{
		pStyle = new CLibStyle();
		pStyle->Serialize(ar);
		mapStyle->AddTail(pStyle);
	}

So far it's very basic but this is where we have a big problem because it happens that this deserialization, as simple as it is, allocates pointers m_pFont on the same memory areas from one loop to another. With the same archive file, this problem does not necessarily arise depending on whether you are in Debug or in Release, or even differs from one PC to another. Unsure | :~

Afterwards, we inevitably have problems even if the pointers are destroyed ...

Any ideas for ensuring that pointers are not allocated on the same memory range?

Thanks a lot for your help.

modified 25-May-20 3:49am.

Re: Problem with pointers memory allocation on the same memory area

Stephane Capo24-May-20 21:19

Stephane Capo

24-May-20 21:19

Hello,

I'm not sure to understand how the "serialization" works in your exemple.

What is ar ?

C++

ar >> m_pFont

m_pFont is a pointer, so in my opinion, there is no allocation here, only a pointer (ar) affected to another pointer (m_pFont). You probably have one instance of your font ( managed by your code or the library, I don't know ) referenced ( pointed ) by several m_pFont.

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan24-May-20 21:29

Richard MacCutchan

24-May-20 21:29

Stephane Capo wrote:
What is ar ?

It is an instance of CArchive Class | Microsoft Docs[^]

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan24-May-20 21:25

Richard MacCutchan

24-May-20 21:25

You appear to be confusing serialization and deserialization. The first line above ar >> m_pFont; is deserializing from the archive into the m_pFont object. So where is the deserialize code that loads the object from the archive, and what type is m_pFont?

Re: Problem with pointers memory allocation on the same memory area

Member 959508024-May-20 21:52

Member 9595080

24-May-20 21:52

You are right. I've just modified and corrected my previous post ...

Re: Problem with pointers memory allocation on the same memory area

Member 959508024-May-20 22:40

Member 9595080

24-May-20 22:40

Well, in fact, I've two cases :

if I serialize with the following way, I've got some CLibStyle::m_pFont on the same memory during the serialization :

C++

CLibStyle Style;
for (int nNumRow = 0; nNumRow ++; nNumRow <nNbRow)
	for (int nNumCol = 0; nNumCol ++; nNumCol <nNbCol)
	{
		Style.Free();
		m_pGrid->GetStyleRowCol( nRow, nCol, Style);
		Style.Serialize(ar);
	}

if I serialize with this second way, I've got problem during deserialization in the ar >> m_pFont line : CArchive::ReadObject can't find the corresponding runtime class ...

C++

CLibStyle *pStyle;
for (int nNumRow = 0; nNumRow ++; nNumRow <nNbRow)
	for (int nNumCol = 0; nNumCol ++; nNumCol <nNbCol)
	{
		pStyle = new CLibStyle();
		m_pGrid->GetStyleRowCol( nRow, nCol, *pStyle);
		pStyle->Serialize(ar);
	}

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan24-May-20 22:54

Richard MacCutchan

24-May-20 22:54

Well your code remains unclear. However, if m_pFont is a pointer, then you are going to have problems unless you also serialize the object that it is pointing at. Deserializing a pointer without the underlying object means that it will be pointing to some random portion of memory.

Re: Problem with pointers memory allocation on the same memory area

Member 959508024-May-20 23:03

Member 9595080

24-May-20 23:03

This point is treated by the MFC CArchive::ReadObject and CArchive::WriteObject methods which are automatically called by the >> or << operator. They are able to detecte or serialize the associated RuntimeClass.

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan24-May-20 23:19

Richard MacCutchan

24-May-20 23:19

Well if that is working then you need to use your debugger to find out what is going wrong. Also it is still not clear exactly what is wrong when you have deserialized from the archive.

The comments at Storing and Loading CObjects via an Archive | Microsoft Docs[^] seem to imply that you may need to use the Serialize function rather than the insertion/extraction operators.

Re: Problem with pointers memory allocation on the same memory area

Member 95950801-Jun-20 20:36

Member 9595080

1-Jun-20 20:36

Thanks for this interesting link.

This one is also interesting : TN002: Persistent Object Data Format | Microsoft Docs

Re: Problem with pointers memory allocation on the same memory area

phil.o25-May-20 0:21

phil.o

25-May-20 0:21

The most obvious flaw I can see is that your are interverting loop test and variable increment in your for loops.
The syntax is

C++

for (init; condition; increment)

, and you are using

C++

for (init; increment; condition)

instead.

"Five fruits and vegetables a day? What a joke!
Personally, after the third watermelon, I'm full."

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan25-May-20 0:31

Richard MacCutchan

25-May-20 0:31

Well spotted, but I would expect his app to crash if that is in the actual running system.

Re: Problem with pointers memory allocation on the same memory area

Member 959508025-May-20 1:25

Member 9595080

25-May-20 1:25

Yes, very well spotted ... I wrote the sample code too quickly Wink | ;)

Re: Problem with pointers memory allocation on the same memory area

phil.o25-May-20 1:36

phil.o

25-May-20 1:36

I also wonder why these loops are needed, since you do not even use nNumRow and nNumCol in the loops. What is the relation of the loop variables nNumRow and nNumCol to the ar variable?

"Five fruits and vegetables a day? What a joke!
Personally, after the third watermelon, I'm full."

Re: Problem with pointers memory allocation on the same memory area

Richard MacCutchan25-May-20 1:46

Richard MacCutchan

25-May-20 1:46

It is no wonder we are getting confused if you are not even showing the actual code that has the problem.

Re: Problem with pointers memory allocation on the same memory area

Member 95950801-Jun-20 20:42

Member 9595080

1-Jun-20 20:42

Thank you all for your help.

The example code is very close to the actual code and the problem is that sometimes, depending on the computer, because of the operator >> to deserialize the style m_pFont, several m_pFont pointed to the same memory area.

I studied the problem with a minimal grid ... and finally realized that in my application I was not using this m_pFont. I modified my code so that I would no longer use it at all, destroy it and set it to NULL which definitively resolved my problem.

If I don't fully explain the phenomenon, I think it comes from the fact that these m_pFont contained the same data and that the operators << consider the pointer had already been serialized as explained in the TN002: Persistent Object Data Format | Microsoft Docs ... Maybe ...

Regards

Printing With Crystal Report

a_alise21-May-20 11:09

a_alise

21-May-20 11:09

Any Thing To Send Data To Crystal Report By VC++ 6.0
,We Can Say , PrintOut Method
Object : Change No Copies Dynamic Through Code

Re: Printing With Crystal Report

_Flaviu22-May-20 0:12

_Flaviu

22-May-20 0:12

Other application can print out without problem ? Have tried to print to another printer ? Or, have you tried to run that command on another machine ? You can find more if you do some debugging on your code ...

modified 24-May-20 2:43am.

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