Software USB write blocker for linux - C / C++ / MFC Discussion Boards

Re: Operator overload question

CPallini7-Apr-14 2:28

CPallini

7-Apr-14 2:28

Please don't do that.
Such a operator should only return a MyString reference.

Veni, vidi, vici.

Re: Operator overload question

econy7-Apr-14 5:51

econy

7-Apr-14 5:51

but, I use :

C++

return MyString(newStr);

I got a compile error message.

Re: Operator overload question

CPallini7-Apr-14 6:21

CPallini

7-Apr-14 6:21

You have to change the method signature.
It is safe to add a C-like string to a MyString object and then return a reference to the latter:

C++

MyString & operator+(MyString & iMyStr, const char * str);

Veni, vidi, vici.

Reference variable assignment and copy constructor call

trinh.nguyen4-Apr-14 19:05

trinh.nguyen

4-Apr-14 19:05

I am testing the constructor call with the code below:

#include <iostream>

class A
{
public:
    A(int n = 0)
        : m_n(n)
    {

    }

    A(const A& a)
        : m_n(a.m_n)
    {

    }

private:
    int m_n;
};


int main()
{
    A a(2), b(1);

    const A c(a);

    const A &d = c;

    const A e = b; //Note 1

    b = d; //Note 2: I am confused here

    return 0;
}

Everything is OK with me.

But there is one point that I cannot understand is that: At the line "b = d" (Note 2), why the copy constructor is not called while at the line "const A e = b" (Note 2) the constructor is called?

I expect that at line Note 2, the copy constructor will be called to copy the value of "c" (referenced by "d") to "b", but it doesn't happen.

Please explain it, thank you in advance!

Re: Reference variable assignment and copy constructor call

Randor 4-Apr-14 21:47

Randor

4-Apr-14 21:47

Hi,

You are not invoking the assignment operator with your const A e = b;. You are constructing a new object of const A e and performing initialization by copy of b.

This is covered in section 8.5 paragraph 15 of the latest standard.

www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3690.pdf‎[^]

Best Wishes,
-David Delaune

Re: Reference variable assignment and copy constructor call

trinh.nguyen4-Apr-14 23:10

trinh.nguyen

4-Apr-14 23:10

Thanks Randor for your prompt reply.

As your answer, I can conclude that the copy constructor will be call for initialization only, not for "=" (assignment operator). Since long time ago, I have believed that the copy constructor will be call for "=" operator if there is no "=" operator defined for that class.

But I still wonder this: If there is no "=" operator defined for that class, what will be implemented for "=" operator? Binary copy?

Thanks.

Re: Reference variable assignment and copy constructor call

Randor 4-Apr-14 23:57

Randor

4-Apr-14 23:57

Hi,

trinh.nguyen wrote:
But I still wonder this: If there is no "=" operator defined for that class, what will be implemented for "=" operator? Binary copy?

If you do not write an assignment operator for your class the compiler will generate a default assignment operator that performs a memberwise copy[^] of base classes and members.

Have a look at section 12.8 paragraph 15:

www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3690.pdf[^]

Best Wishes,
-David Delaune

Software USB write blocker for linux

dream qq4-Apr-14 13:32

dream qq

4-Apr-14 13:32

Hello,
I want to make a USB write blocker with c++ to work for linux. I have been looking for open source USB write blockers, but I just found few for windows that disable the writing functionality from the registry. The idea is to prevent the OS from changing the USB devices timestamps while plugging the device for cloning or analysis the data.
I need help in figure out the best way to do it.
Thank you.

How to change tab event of property sheet

kangte22223-Apr-14 15:15

kangte2222

3-Apr-14 15:15

Override ::
MSVC > Class View > Properties > Override >
OnKillActive , OnSetActive

/*Dialog ( in sheet page ) */
virtual BOOL OnKillActive();
virtual BOOL OnSetActive();

/*exit page*/
BOOL CMyPropertyPage1::OnKillActive()
{

TRACE(_T("OnKillActive\n"));
return CMFCPropertyPage::OnKillActive();
}

/* entrance page*/
BOOL CMyPropertyPage1::OnSetActive()
{

TRACE(_T("OnSetActive\n"));
return CMFCPropertyPage::OnSetActive();
}

Visual C

Re: How to change tab event of property sheet

David Crow3-Apr-14 16:43

David Crow

3-Apr-14 16:43

Do you have a specific question, or are you just posting random code? Confused | :confused:

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Re: How to change tab event of property sheet

Malli_S3-Apr-14 23:59

Malli_S

3-Apr-14 23:59

What is the question?

Please go through the guidelines HOW-TO-ASK-A-QUESTION[^] before posting the question.

[Delegates] [Virtual Desktop] [Tray Me !]

-Malli...!

Re: How to change tab event of property sheet

Randor 4-Apr-14 8:56

Randor

4-Apr-14 8:56

Hi,

You should be getting a CPropertyPage::OnKillActive [^]call when you tab to the next page. If this is not working... then the way to debug this would be checking the CWnd::OnNotify[^] handler and make sure your WM_NOTIFY is not consuming the PSN_KILLACTIVE notification code[^].

Best Wishes,
-David Delaune

GetWindowRect(),GetClientRect() question

econy3-Apr-14 8:42

econy

3-Apr-14 8:42

Hi, I am confused with screen/window/client coordinate in windows programming.
As I understand, 3 coordinates are like the following:
screen top left point: spoint(Xs,Ys);
window top left point: wpoint(Xw,Yw);
client top left point: cpoint(Xc,Yc);

so the related position for 3 points are:

spoint -----------
  |  wpoint----------
  |    | 
       |    cpoint ----------
               |
               |

GetWindowRect(&rect) gets wpoint;
ScreenToClient(&rect) gets which point? if it gets cpoint,then
cpoint (x,y) based on wpoint, or spoint?

And in a dialog template:

  CONTROL         "",IDC_STATIC_TST,"Static",SS_BLACKFRAME,80,83,118,35
80,83,118,35 based on client top left point?

Re: GetWindowRect(),GetClientRect() question

Randor 3-Apr-14 9:08

Randor

3-Apr-14 9:08

Hi,

It's all relative, my dear Watson.

econy wrote:
ScreenToClient(&rect) gets which point?

ScreenToClient will convert a screet RECT (your 'spoint') coordinates to be relative to client RECT (your 'cpoint'). In your example the top and left will be negative coordinates relative to the client top/left.

Window Coordinate System[^]

Best Wishes,
-David Delaune

solar irradiance c++ program

Member 107223713-Apr-14 6:53

Member 10722371

3-Apr-14 6:53

Hi

I am new to c++ and I have an assignment to write a program to compute the Average daily solar energy collectable from January 1st to December 31st per square meter (kWh/m^2/day) using a 2-axis tracking collector in Albuquerque, can any one help me with this

Re: solar irradiance c++ program

Albert Holguin3-Apr-14 7:00

Albert Holguin

3-Apr-14 7:00

Well... get started and ask specific questions. I think you'll get more fruitful responses that way. Good luck!

Re: solar irradiance c++ program

Member 107223713-Apr-14 7:13

Member 10722371

3-Apr-14 7:13

Thanks Albert

I will attached more specific information

Re: solar irradiance c++ program

fat___boy3-Apr-14 10:25

fat___boy

3-Apr-14 10:25

Its very simple, from an IT perspective. Your hardware, whatever it is that measures radiation, plugs into your serial/USB port, your app opens that, and takes readings on a periodic basis, collates them, and averages them.

The problem is how you distinguish solar radiation at the surface from back radiation from GH gasses. (assuming you will be measuring at the surface and not TOA).

reading stdout

C^hris L^osinger3-Apr-14 5:52

C^hris L^osinger

3-Apr-14 5:52

i have a library, which i can not modify. this library is called from a console app, and as part of its processing, this library dumps a large and variable amount of debug/trace info to stdout. i'd like to be able to read what the library is sending to stdout from the calling code, in order to extract certain pieces of info for analysis. basically, i want to capture some of what the library prints during a call, save that info away until the call completes, then re-print the info in a better format. this would help me from having to search the hundreds of lines of output to find the particular bits i need.

(this is Windows, C++)

is such a thing possible?

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Re: reading stdout

Albert Holguin3-Apr-14 7:05

Albert Holguin

3-Apr-14 7:05

Have you tried redirection operators[^]?

Re: reading stdout

C^hris L^osinger3-Apr-14 7:08

C^hris L^osinger

3-Apr-14 7:08

i need to do this within the calling app, not from the shell.

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Re: reading stdout

Albert Holguin3-Apr-14 7:15

Albert Holguin

3-Apr-14 7:15

Do you need this for trouble-shooting or all the time? ...because it sounded like you just needed for troubleshooting, in which case... why not use the shell options?

..but otherwise, you can always try reassigning the stream using freopen[^].
Here's an actual example...
http://support.microsoft.com/kb/58667[^]

Re: reading stdout

C^hris L^osinger3-Apr-14 7:17

C^hris L^osinger

3-Apr-14 7:17

Albert Holguin wrote:
Do you need this for trouble-shooting or all the time

all the time.

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Re: reading stdout

Albert Holguin3-Apr-14 7:26

Albert Holguin

3-Apr-14 7:26

Ok, try out the freopen option... hopefully that gets the job done.

Re: reading stdout

Randor 3-Apr-14 8:37

Randor

3-Apr-14 8:37

Hey Chris,

Creating a Child Process with Redirected Input and Output[^]

If you don't get any redirected output from the sample above... then your third-party console app might be writing to the STD_ERROR_HANDLE rather than the STD_OUTPUT_HANDLE. GetStdHandle function[^].

Best Wishes,
-David Delaune

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.