C / C++ / MFC Discussion Boards

Struct with union with different sized members - How can I declare the smallest struct?

arnold_w6-Mar-22 1:17

6-Mar-22 1:17

I am writing code in standard C for a microcontroller (STM32L) and I compile with GCC. I have a struct that contains a union and the union can be of different size:

struct MyStruct
{
    int someInteger;
    union
    {
        int smallMember[1];
        int bigMember[1000];
    } smallOrBigMember;
};

Is it possible for me to declare an object of MyStruct that only occipies 8 bytes of memory if I only intend to use the smallMember of that object?

Re: Struct with union with different sized members - How can I declare the smallest struct?

Mircea Neacsu6-Mar-22 2:39

Mircea Neacsu

6-Mar-22 2:39

No, you cannot. If you need a flexible size structure, the idiomatic solution is to add a zero size array at the end of the structure. Then, presumably, one of the fixed length fields tells you the size of the variable part. Something like this:

C++

struct MyStruct
{
  int small_or_big;
  int variable_part[0]; //or int variable_part[] if you want to conform to C90
};

struct MyStruct *ptr;
if (ptr->small_or_big == BIG_STRUCT)
{
  ptr->variable_part[999] = some_value; //we know that variable part size is 1000
  //...
}

When you allocate the structure you have to account for the variable part:

C++

//...
ptr_small = malloc(sizeof(MyStruct) + SIZE_OF_SMALL_PART);
ptr_small->big_or_small = SMALL_STRUCT;

ptr_big = malloc (sizeof(MyStruct) + SIZE_OF_BIG_PART);
ptr_big->big_or_small = BIG_STRUCT;

Mircea

modified 6-Mar-22 11:10am.

Line Break Rich Edit

ForNow5-Mar-22 17:42

ForNow

5-Mar-22 17:42

I have been using carriage return 0X0AD line feed 0A to break lines on Rich Edit using SF_TEXT until I noticed some of the data I am trying to Dump contains a 0x0d 0X0A causing an inadvertent line break
is there an another way to break lines

Thanks

Re: Line Break Rich Edit

Richard Andrew x646-Mar-22 4:33

Richard Andrew x64

6-Mar-22 4:33

I think what you need to do is find another way to represent the 0xAD data so that it doesn't trigger a line break. Like use a special character to represent it in the data stream that you're loading into the control.

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

Re: Line Break Rich Edit

ForNow6-Mar-22 5:19

ForNow

6-Mar-22 5:19

I thought rich edit uses BOTH CR / LF as new line seems different versions Of Richedit now to 4.1 have different methods of line breaking trying to figure which rich edit dll/class version I am running

C++ even numbers query

Member 1555051328-Feb-22 16:30

Member 15550513

28-Feb-22 16:30

Write a C++ program that reads a positive integer n, and prints the first
n even numbers.

For example, one execution would look like this:
Please enter a positive integer: 3
2
4
6

File Name

evennumbers.cpp

Score

There are three tests each worth 2 points

1.#include<iostream>
2.using namespace std;
3.
4.int main()
5. {
6. int n;
7. cout<<"Please enter a positive integer:";
8. cin>>n;
9.
10. cout<<"These are all even numbers in between 1 to "<

Re: C++ even numbers query

Victor Nijegorodov28-Feb-22 20:31

Victor Nijegorodov

28-Feb-22 20:31

Well, looks like good and not complicated exercise. Did you solve it?

Re: C++ even numbers query

Member 1555051328-Feb-22 21:33

Member 15550513

28-Feb-22 21:33

Hi it's okay when I run it,but the Autograrder says FAILED.What could be the problem? Should I submit the executable file only.If I rename the executable file as .cpp the Autograder results to errors of 2 .cpp files.What should I do please?

Re: C++ even numbers query

Victor Nijegorodov28-Feb-22 23:02

Victor Nijegorodov

28-Feb-22 23:02

Sorry, I could not understand what you mean... Sigh | :sigh:

The code you've posted is not complete, it doesn't compile and it does nothing. Thumbs Down | :thumbsdown:

Re: C++ even numbers query

Member 155505131-Mar-22 17:31

Member 15550513

1-Mar-22 17:31

Re: C++ even numbers query

Victor Nijegorodov1-Mar-22 22:32

Victor Nijegorodov

1-Mar-22 22:32

Please, stop reposting the same! Mad | :mad:

I've already read it (your post from 1-Mar-22 9:33) And answered!

Re: C++ even numbers query

Richard MacCutchan1-Mar-22 22:40

Richard MacCutchan

1-Mar-22 22:40

How do you expect anyone here to answer? We have no idea what the Autograrder is, or what criteria it uses to judge your code. And unless you show the complete code we cannot suggest any changes.

Re: C++ even numbers query

David Crow1-Mar-22 3:50

David Crow

1-Mar-22 3:50

So what's the problem, exactly?

"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: C++ even numbers query

Richard Andrew x642-Mar-22 9:42

Richard Andrew x64

2-Mar-22 9:42

Is there any doubt? He wants someone to do his work. Laugh | :laugh:

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

Christine Belisario25-Feb-22 20:48

Christine Belisario

25-Feb-22 20:48

#include<stdio.h>

int getFactorial(int);

int main(void) {
    int n;
    printf("Enter n: ");
    scanf("%d",&n);

    printf("Factorial of %d is %d", n, getFactorial(n));

    return 0;
}

int getFactorial(int n) {
    // how to Implement this recursive function 
}

Re: C

Richard MacCutchan25-Feb-22 22:52

Richard MacCutchan

25-Feb-22 22:52

Christine Belisario wrote:
// how to Implement this recursive function

Google will find you many explanations of the factorial function. You just need to think about how you could implement it in code.

Re: C

RedDk26-Feb-22 8:47

RedDk

26-Feb-22 8:47

When you've got a plank of code like this, and haven't necessarily begun stepping a mast of methods by leafing through your function library, presumeably squirreled away in the hold in a rat-free database, sometimes it's best to just go to a search engine that's got three sheets to the wind (open to the public), type in each word grain separated by commas and hammer the return.

And marking the returns using your favorites folder by hanging the list of code fragments off the hook of the internet browser you're buckling, for future reference, you're well on your way to driving the sea with your bark of ... lively functions ... and saving CP from a dumb trend which is hopefully on it's way south.

Re: C

Greg Utas26-Feb-22 10:32

Greg Utas

26-Feb-22 10:32

Prize winner for metaphor density. Big Grin | :-D

Robust Services Core | Software Techniques for Lemmings | Articles
The fox knows many things, but the hedgehog knows one big thing.

how to dynamically delete sub-control created in run-time

wuxianzhong18-Feb-22 15:54

wuxianzhong

18-Feb-22 15:54

first of all, i shall thanks all of you guys.
In my project, i created some STATIC & EDIT controls in a CDialog and set these control's parent to a group box(also a STATIC control).
it works well for create, but it can't be delete dynamically.
For example, i create 5 EDIT control then delete it(there are no sub-controls in group box this time), and i create 2 EDIT control again, oops! there are 5 EDIT control showing in the group box. So, i guess this caused by the group box haven't refreshed in time. and then i sendmessage to group box to force it to refresh. unfortunately it doesn't works.
here is my code:
<pre lang="C++">
void CPLCDlg::DynamicCreateEdit(UINT nNums)
{
const int YSpace = 15;
const int EHeight = 20;
const UINT EDITID = 72000;
if (nNums <= 0)
return;
CButton* pGroup = (CButton*)GetDlgItem(IDC_STATIC_GROUP);
if (NULL != pGroup)
{
if (NULL != m_pDynEdit && m_siNumsOfDynEdit > 0)
{
for (short i = 0; i < m_siNumsOfDynEdit; i++)
{
if (NULL != m_pDynEdit[i].GetSafeHwnd())
{
m_pDynEdit[i].ShowWindow(SW_HIDE);
m_pDynEdit[i].DestroyWindow();
}
delete m_pDynEdit[i];
}
delete[] m_pDynEdit;
m_pDynEdit = NULL;
::SendMessage(pGroup->GetSafeHwnd(), WM_ERASEBKGND, 0, 0);
}
pGroup->Invalidate(FALSE);
pGroup->RedrawWindow();
pGroup->UpdateWindow();
CRect rcPos;
CString str;
rcPos.SetRectEmpty();
m_pDynEdit = new CEdit[nNums]();
for (short i = 0; i < nNums; i++)
{
rcPos.left = 10;
rcPos.top = 20 + (EHeight + YSpace) * i;
rcPos.right = rcPos.left + 30;
rcPos.bottom = rcPos.top + EHeight;
str.Empty();
str.Format(_T("%d"), i + 1);
if (m_pDynEdit[i].CreateEx(WS_EX_STATICEDGE, _T("EDIT"), (LPCTSTR)str, ES_CENTER | WS_VISIBLE | WS_CHILD | WS_TABSTOP, rcPos, pGroup, EDITID + i))
{
//m_pDynEdit[i].SetWindowText(_T("0"));
}

}
m_siNumsOfDynEdit = nNums;
}
}

</pre>

Re: how to dynamically delete sub-control created in run-time

Gerry Schmitz18-Feb-22 20:30

Gerry Schmitz

18-Feb-22 20:30

Just recreate the dialog? Place it over the old and delete the old, if it's noticeable. (25 cent solution)

"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I

Re: how to dynamically delete sub-control created in run-time

Victor Nijegorodov18-Feb-22 21:18

Victor Nijegorodov

18-Feb-22 21:18

Rather than destroy and recreate just hide and then show again them!
Do destroy/delete only by destroying the dialog itself!

Re: how to dynamically delete sub-control created in run-time

Randor 19-Feb-22 6:27

Randor

19-Feb-22 6:27

Looks like you send a WM_ERASEBKGND message to the parent group window (pGroup) and then redraw it. But parent windows will clip the child windows[^]. This is why you still see the windows you deleted.

In other words when you invalidate/redraw pGroup it skips over the rectangles where your m_pDynEdit child windows were being drawn.

You can use the ExcludeClipRect function[^] to remove the clipped rectangles from the clipping region.

Also, you can use the RectVisible function[^] to check for clipping.

I'm on a TV, I apologize in advance for any typos.

Azure DevOps Chocolatey question : install vs2022

Maximilien17-Feb-22 7:52

Maximilien

17-Feb-22 7:52

(I'm not sure there's a better place to ask)

I'm trying to use VS2022 in our build pipeline.

I have a pipeline like this :

Quote:
pool:
vmImage: 'windows-latest'

variables:
solution: 'MySolution.sln'

steps:

task: CmdLine@2
displayName: 'Choco install additional packages'
inputs:
script: |
choco install windows-sdk-8.1 visualstudio2017community microsoft-build-tools-2013 visualstudio2022professional
task: VSBuild@1
displayName: 'Build Debug143|x64'
inputs:
vsVersion: '17.0'
solution: '$(solution)'
maximumCpuCount: true
msbuildArchitecture: 'x64'
platform: 'x64'
configuration: 'Debug143'

I get errors that it cannot find the installation.

Quote:
2022-02-17T18:46:30.0197396Z ##[error]MyProject.vcxproj(77,3): Error MSB4019: The imported project "C:\Program Files\Microsoft Visual Studio\2022\Professional\MSBuild\Microsoft\VC\v170\Microsoft.Cpp.Default.props" was not found. Confirm that the expression in the Import declaration "C:\Program Files\Microsoft Visual Studio\2022\Professional\MSBuild\Microsoft\VC\v170\Microsoft.Cpp.Default.props" is correct, and that the file exists on disk.

When I put a "dir /s" in my pipeline, it looks like VS2022 is not installed in that path.

I'm not sure what I have to do to make it work.

Any Idea ?
Thanks.

CI/CD = Continuous Impediment/Continuous Despair

Re: Azure DevOps Chocolatey question : install vs2022

Mircea Neacsu17-Feb-22 8:02

Mircea Neacsu

17-Feb-22 8:02

Not sure if it applies to you but this is the magic incantation I use find latest VS installation:

BAT

@echo off
rem
rem Setup environment for MSBuild 2017 and later rem

if not "%VSCMD_VER%"=="" (
  echo MSBuild environment is already set
  goto :EOF
) 
rem VS2017U2 contains vswhere.exe if "%VSWHERE%"=="" set "VSWHERE=%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe"

for /f "usebackq tokens=*" %%i in (`"%VSWHERE%" -latest -products * -requires Microsoft.Component.MSBuild -property installationPath`) do (
  set VSInstallDir=%%i
)
rem echo Visual studio installation folder is: %VSInstallDir% rem "%VSInstallDir%\common7\tools\vsdevcmd.bat" "%VSInstallDir%\common7\tools\vsmsbuildcmd.bat"

Mircea

Re: Azure DevOps Chocolatey question : install vs2022

Maximilien18-Feb-22 3:23

Maximilien

18-Feb-22 3:23

Thanks I will look at it.
Thumbs Up | :thumbsup:

CI/CD = Continuous Impediment/Continuous Despair

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