C / C++ / MFC

Re: Condition variable question

4-Aug-18 9:32

Possibly, but threads do not always behave the way you expect.

focusdoit4-Aug-18 16:30

focusdoit

4-Aug-18 16:30

Sure, the code is embedded software code, no OS, so, do you think there is a better way to implement the condition variable?

Re: Condition variable question

Richard MacCutchan4-Aug-18 20:57

A Problem in Writing Shared Memory to windows from a C++ application

4-Aug-18 20:57

That's a whole new question.

D_code_writer2-Aug-18 5:00

Re: A Problem in Writing Shared Memory to windows from a C++ application

2-Aug-18 5:00

Hey Guys,

I'm writing an application in C++ that needs to write shared memory to windows and I've hit a stumbling block.

Even though I'm not getting any error messages (I've stepped through with the debugger) it would appear nothing is writing to shared memory. Here is the code that writes the shared memory,

void Write_Physics(PhysicsStruct *s_physics)
{
//	Create the shared memory
	TCHAR szName[] = TEXT("Local\\physics");
	hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(PhysicsStruct), szName);
	if (!hMapFile)
	{
		return;
	}

	//	Open the buffer for file read and write
	mapFileBuffer = (unsigned char*)MapViewOfFile(m_physics.hMapFile, FILE_MAP_ALL_ACCESS, 0, 0, sizeof(PhysicsStruct));
	if (!mapFileBuffer)
	{
		return;
	}
	
	//	Copy the physics pointer over
	CopyMemory(mapFileBuffer,s_physics,sizeof(PhysicsStruct));
	//_getch();
	

	//	Write the shared memory
	UnmapViewOfFile(m_physics.mapFileBuffer);
	CloseHandle(m_physics.hMapFile);
}

My difficulty is that when I try another process to read the shared memory nothing is happening. For completeness here is the code that reads the structure from the shared memory,

void Read_Physics(PhysicsStruct *s_physics)
{
	//	Create the shared memory
	TCHAR szName[] = TEXT("Local\\physics");
	hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(PhysicsStruct), szName);
	if (!m_physics.hMapFile)
	{
		return;
	}

	//	Open the buffer for file read and write
	mapFileBuffer = (unsigned char*)MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, sizeof(PhysicsStruct));
	if (!mapFileBuffer)
	{
		return;
	}

	s_physics = (PhysicsStruct*)mapFileBuffer;

	//	Write the shared memory
	UnmapViewOfFile(mapFileBuffer);
	CloseHandle(hMapFile);	
}
//-----------------------------------------------------------------------

If anyone has any suggestions it would be greatly appreciated. What the problem resembles is like trying to write something to file and forgetting the fprintf or file write commands.

Thanks in advance guys.

Richard Andrew x642-Aug-18 13:00

Re: A Problem in Writing Shared Memory to windows from a C++ application

2-Aug-18 13:00

Where is hMapFile declared?

void Read_Physics(PhysicsStruct *s_physics)
{
	//	Create the shared memory
	TCHAR szName[] = TEXT("Local\\physics");
here >>>>	hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(PhysicsStruct), szName);
	if (!m_physics.hMapFile)
	{
		return;
	}

	//	Open the buffer for file read and write
	mapFileBuffer = (unsigned char*)MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, sizeof(PhysicsStruct));
	if (!mapFileBuffer)
	{
		return;
	}

	s_physics = (PhysicsStruct*)mapFileBuffer;

	//	Write the shared memory
	UnmapViewOfFile(mapFileBuffer);
	CloseHandle(hMapFile);	
}

The difficult we do right away...
...the impossible takes slightly longer.

Richard Andrew x642-Aug-18 13:06

Re: A Problem in Writing Shared Memory to windows from a C++ application

2-Aug-18 13:06

There is another problem with the code for the Read function:

You're passing the pointer s_physics by value. This is not going to do what you want. You need to pass the pointer's address.

You would do that like so:

C++

void Read_Physics(PhysicsStruct **s_physics)

Then inside the function:

C++

*s_physics = (PhysicsStruct*)mapFileBuffer;

And the read function would be called thusly:

C++

Read_Physics(&s_physics);

The difficult we do right away...
...the impossible takes slightly longer.

D_code_writer2-Aug-18 20:24

Re: A Problem in Writing Shared Memory to windows from a C++ application

2-Aug-18 20:24

Richard,

Many thanks for answering. My apologies I wrote this as pseudo code to try and save time. The declarations for those are,

HANDLE hmapFile;
unsigned char *mapFileBuffer;

They are at the beginning of each function. The joys of doing this at 1:00am!

Copy you on the declaration of the read function - leave that with me to sort out.

Apart from this is there any other reason you can see for this and particular the write function not working?

Many thanks in advance.

Richard Andrew x643-Aug-18 2:41

Re: A Problem in Writing Shared Memory to windows from a C++ application

3-Aug-18 2:41

D_code_writer wrote:
I wrote this as pseudo code to try and save time.

It's not helpful if you post code that is not the actual code that is causing the problem.

I can see one other BIG problem:

You're setting s_physics to point to the memory of the file map, but then you're closing the file mapping!

EDIT:
The problem is the same with the write function. You're writing to the memory, but then you're closing the file mapping! The read function cannot read from a file mapping that doesn't exist.

I think this is the main reason it's not working. You need to copy the memory pointed to by mapFileBuffer, and return that as your result. Then you'll need to free this memory somewhere else.

So, in pseudo code:

Read Function:
Create File Map;
Allocate new memory = sizeof(PhysicsStruct);
Copy memory from File Map to new memory;
Set s_physics = new memory;
return s_physics;

The difficult we do right away...
...the impossible takes slightly longer.

modified 3-Aug-18 8:48am.

D_code_writer3-Aug-18 12:45

Re: A Problem in Writing Shared Memory to windows from a C++ application

3-Aug-18 12:45

Richard,

Copy that - I actually figured it out. I found an old VC++ 6 project called MMFAPP1. That actually worked. Here is the crux of the fix.

Declare the following variables,

HANDLE m_hFileMMF;      // memory mapped file
    LPVOID m_pViewMMFFile;       // view of file, contains text in edit box

Then create the file handle,

m_hFileMMF = CreateFileMapping(INVALID_HANDLE_VALUE,NULL,PAGE_READWRITE,0,4*1024,"MyMMF");              
    DWORD dwError = GetLastError();
    if ( ! m_hFileMMF )
    {
        MessageBox(_T("Creation of file mapping failed"));
    }
    else
    {
        m_pViewMMFFile = MapViewOfFile(m_hFileMMF,FILE_MAP_ALL_ACCESS,0,0,0);                         // map all file

        if(! m_pViewMMFFile )
        {
            MessageBox(_T("MapViewOfFile function failed"));
        }
    }

Once that is done to write the data to the shared memory we have

PhysicsStruct s_physics;

if(m_pViewMMFFile )
			CopyMemory(m_pViewMMFFile,&s_physics,sizeof(PhysicsStruct));

To read from the shared memory we have,

if(m_pViewMMFFile )
			CopyMemory((PVOID)&s_physics,m_pViewMMFFile,sizeof(SPageFilePhysics));

I tested that and it worked like a charm. Also many thanks to the guy who wrote MMFAPP1 in the first place. It saved my neck. Also Richard thanks for your help as well.

Richard Andrew x643-Aug-18 13:44

Re: A Problem in Writing Shared Memory to windows from a C++ application

3-Aug-18 13:44

Glad you got it sorted. Smile | :)

The difficult we do right away...
...the impossible takes slightly longer.

D_code_writer3-Aug-18 14:05

Re: CEditCtrl in FrameWnd

3-Aug-18 14:05

So am I!! Thanks again for your help

CEditCtrl in FrameWnd

john56321-Aug-18 23:50

john5632

1-Aug-18 23:50

Hi I need to create edit control on frame window.
please suggest to do so?

Richard MacCutchan2-Aug-18 0:35

Re: CEditCtrl in FrameWnd

2-Aug-18 0:35

See CEdit Class | Microsoft Docs[^]. In future it would help if you provided a proper description of your problem.

Jochen Arndt2-Aug-18 0:51

Jochen Arndt

2-Aug-18 0:51

I already answered that in reply to CEditCtrl in FrameWnd:
Frame windows do not contain user controls. Those should be part of views which in turn are hosted by frame windows.

Re: CEditCtrl in FrameWnd

Victor Nijegorodov2-Aug-18 1:01

Victor Nijegorodov

2-Aug-18 1:01

You could use CEdit::Create method.
However, as already mentioned, there is rarely or maybe not at all a good idea to create control in the frame window.

Run CFile::Open as admin

_Flaviu1-Aug-18 21:47

_Flaviu

1-Aug-18 21:47

Is there possible to run CFile::Open in order to write a text file, inside C:\Program Files\ location, with administrator rights, even the application who call this are not started with administrator rights ?

Re: Run CFile::Open as admin

Jochen Arndt1-Aug-18 22:54

Jochen Arndt

1-Aug-18 22:54

There is no way. A running process can not get higher privileges.

All you can do is starting another process using ShellExecuteEx with the "runas" verb which usually shows the UAC prompt.

Another option is running your application with sufficient priviliges and drop those when no longer needed. See permissions - Dropping privileges in C++ on Windows - Stack Overflow[^].

See also the CP article Riding the Vista UAC elevator, up and down[^].

But I suggest to rethink your request. An application should not modify data in the Program Files directory tree. That should be only modified by installation and update processes. Windows provides common directories for application specific data (shared and per user).

Re: Run CFile::Open as admin

_Flaviu1-Aug-18 23:00

_Flaviu

1-Aug-18 23:00

Ok, understood. Thank you.

execl in c++ example

Shaul.amir30-Jul-18 22:12

Shaul.amir

30-Jul-18 22:12

need example

Re: execl in c++ example

Jochen Arndt30-Jul-18 23:02

Jochen Arndt

30-Jul-18 23:02

Using your subject with a search engine should give you multiple results.

But read the function documentation first to understand the examples.

_execl, _wexecl | Microsoft Docs[^]
_exec, _wexec Functions | Microsoft Docs[^] (with example code)
exec(3) - Linux manual page[^]
exec family of functions in C - GeeksforGeeks[^] (with example code)

help me~ for use..... #define macro ## #@ #

dsyoon ds29-Jul-18 17:00

dsyoon ds

29-Jul-18 17:00

#define FUNC_1(x) (x+1)
#define FUNC_2(x) (x+2)
#define FUNC_3(x) (x+3)
#define FUNC_4(x) (x+4)

#define FUNC_N(n, x) (FUNC_##n(x))

----------------------------------------

int result1 = FUNC_N(1, 100);//OK

but i want to below:
int a = 1;
int result2 = FUNC_N(a, 100);//NG

please help ~

Re: help me~ for use..... #define macro ## #@ #

Daniel Pfeffer29-Jul-18 20:45

Daniel Pfeffer

29-Jul-18 20:45

Please don't cross-post. See my answer in Algorithms.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.

The new upgrade system

Anthony Appleyard28-Jul-18 12:50

Anthony Appleyard

28-Jul-18 12:50

I have used Visual C++ for many years without trouble.

But in the last few days, an automatic upgrade came: it shows a MessageBox that says "One-way upgrade. Visual Studio will automatically make functional changes to the following projects in order to open them. ...".

With one of my projects (called 'dragclip_vc'), today, however often I open it and look in it and close it, the new upgrade system shows and needs attention, every time I open that project, and it does not preserve the display of opened files. Please how can I stop that from happening? (I know that the automatic upgrade needs doing once for each of my projects.)

(Another of my projects (called 'makeobj_vc') auto-upgraded correctly and did not ask again for upgrading, and it preserves the display of opened files.)

dragclip_vc is a very small project; all that it does is that if I drag a file into it from a directory display, it puts that file's full pathname in the Windows clipboard. It is useful.

makeobj_vc is a big project.

The '_vc' on the ends of their names means "for Visual C++"; it is to distinguish from old versions that I had written for Borland C.

modified 29-Jul-18 2:41am.

Re: The new upgrade system

Anthony Appleyard28-Jul-18 18:35

Anthony Appleyard

28-Jul-18 18:35

The affected project ('dragclip_vc') is still doing it this morning (5.37 a.m. by UK time), and wanting this upgrade every time that I open it.

The other mentioned project ('makeobj_vc') opened correctly this morning and did not ask for this upgrade again.

If needed, I have old backup copies of all my Visual C++ projects on an offload-disk.

modified 29-Jul-18 0:47am.

Re: The new upgrade system

Richard MacCutchan28-Jul-18 22:20