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HOW TO ANSWER A QUESTION

Chris Maunder — Thu, 16 Jul 2009 13:09:00 GMT

Apologies for the shouting but this is important.

When answering a question please:

Read the question carefully
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar
If a question is poorly phrased then either ask for clarification, ignore it, or mark it down. Insults are not welcome
If the question is inappropriate then click the 'vote to remove message' button

Insults, slap-downs and sarcasm aren't welcome. Let's work to help developers, not make them feel stupid.

cheers,
Chris Maunder

The Code Project Co-founder
Microsoft C++ MVP

How to get an answer to your question

Chris Maunder — Thu, 16 Jul 2009 13:05:00 GMT

For those new to message boards please try to follow a few simple rules when posting your question.

Choose the correct forum for your message. Posting a VB.NET question in the C++ forum will end in tears.
Be specific! Don't ask "can someone send me the code to create an application that does 'X'. Pinpoint exactly what it is you need help with.
Keep the subject line brief, but descriptive. eg "File Serialization problem"
Keep the question as brief as possible. If you have to include code, include the smallest snippet of code you can.
Be careful when including code that you haven't made a typo. Typing mistakes can become the focal point instead of the actual question you asked.
Do not remove or empty a message if others have replied. Keep the thread intact and available for others to search and read. If your problem was answered then edit your message and add "[Solved]" to the subject line of the original post, and cast an approval vote to the one or several answers that really helped you.
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cheers,
Chris Maunder

The Code Project Co-founder

Microsoft C++ MVP

AI

Ted Snyders — Sat, 18 Nov 2023 20:52:00 GMT

how do I get started with AI

Help with STL list::insert

ForNow — Wed, 21 Sep 2022 11:54:00 GMT

Hi

I need a little guidance trying to insert a element my element is a structure here below are my data structures

so I define a structure of type tcbholder struct tcbholder tcbx;

I initialize the iterator member with the following code

C++

tcbx.straverse = tcbx.strptr.begin(); // storage discriptor pointer
	tcbx.stdecsx.blktraverse = tcbx.stdecsx.ablkptr.begin(); // begin block pointer

then to insert a blkdesc type I use the following code

C++

tcbx.stdecsx.ablkptr.insert(tcbx.stdecsx.blktraverse,tcbx.stdecsx.ablkdescx);

I then think I would have to bump up the postion of the iterator so I do the following

C++

tcbx.stdecsx.blktraverse++;

after which I get an exception that I went past the end

Any help would be appreciated

thanks

My first question is am I correct that in initalizing the iterator the code is call list::begin

and then to bump up the interator to get next postion its operator ++

C++

struct blkdesc
   {
       char type;
       int blkaddr;
       int blklen;
       //  struct blkdesc* nextblkdesc;
   };
   struct stdecs
   {
       struct vsmdesc stordesc;
       char* tcb;
       struct blkdesc ablkdescx;
       struct blkdesc fblkdescx;
       //  struct stdecs* nextdecs;

       list<blkdesc> ablkptr;
       list<blkdesc>::iterator blktraverse;
       list<blkdesc> fblkptr;
   };

   struct tcbholder
   {
       char* tcb;
       char programname[8];
       //  struct stdecs *storageptr;
       struct stdecs stdecsx;
       list <stdecs> strptr;
       list <stdecs>::iterator stfirstptr;
       list <stdecs>::iterator straverse;
   };

/std:c++20 broke a template class

Member 15671062 — Sun, 12 Jun 2022 20:07:00 GMT

Hi -

I have a template array class based on a std::vector. All worked well w/ c++17, but there is one line I can't seem to port to the new standard. I'm trying to acquire an iterator to the underlying vector.

Any advice is greatly appreciated.

An abbreviated depiction:

C++

template <class Type> class CMy_Array 
{

    private:
		std::vector<Type> m_vItems;

	public:

		CMy_Array()
		{
		}
		virtual ~CMy_Array ()
		{
			m_vItems.clear();
		}
        void InsertAt(int index)
        {

       	//	THE LINE IN QUESTION - trying to acquire an iterator...
        // this worked w/ std:c++17   -

            std::vector<Type>::iterator p =  m_vItems.begin();

        // With c++20, 2 errors occur; 
        // C2760 - syntax error: unexpected token 'identifier', expected ';' , and 
        // C7510 - 'iterator': use of dependent type name must be prefixed with 'typename'

        // Using the documentation for C2760, I modified the line in question as so -

    		std::vector<Type>::iterator p =  static_cast <std::vector<Type>::iterator> m_vItems.begin();

        // This eliminated the C7510 error, but C2760 remains.


        }      
}

how to implement CButton as CListbox item

rtischer8277 — Fri, 06 May 2022 12:51:00 GMT

I see many code projects that enhance the CListBox control, but none that lets each item be another control, like fx CButton. How would one implement that?

How can I get access to CXXView variables from a Parent Class in MFC

Member 15033704 — Tue, 19 Jan 2021 18:34:00 GMT

Hello everybody
I have an SDI solution in MFC. I have created a class with the name of "CLASS A"
and
class CXXView : public CView, public CLASS A

How can I get access to CXXView variables from CLASS A in MFC?

Indeed; DOSE NOT WORK ==> CXXView * pCurrentView = static_cast<cxxview*>(GetActiveView());
Because of this error:
GetActiveView() is undifined (XXView.h is included in CLASS A)

Best Regads

code of this question

avadhnaresh kushwaha — Wed, 12 Aug 2020 18:17:00 GMT

codeNation fresher batch has a tradition of laser tournaments .in laser tag two team play against each other .a team can have any number of players >=1.the two teams can have unequal team member.
for successful completion of this tournament ipshita want that every person must have played every other person as part of different teams.every laser tag match take 30 minutes to complete .now the gaming arena has allowed codeNation to play for a maxima of X hours after which the arena close . given the number of folks in the batch as N you will have to find out if codeNation will be able to finish the tournament before the complex closes?

Keypad locks

kalberts — Sun, 08 Mar 2020 00:23:00 GMT

For those who enjoy playing with algoritms ... A two-step problem: The simple part, make something that works. The difficult part: Provomg that your solution is the optimal one.

Disclaimer: I have no clue about the second part.

Problem: We have a keypad lock at our work facilities. You present your card, and then if the last four digits typed are a valid entry code, the door opens. So if a valid code is 2345, and you type 1234, the door doesn't open. If you then add a 5, the door opens.

An algoritm for trying all possible keys is like the first homework assignment in 101 Elementary Programming.

If you have no knowledge of any entry code, but you know that if the last four digits are correct, the door will open, what will be your dialing strategy for making the minimal nunber of keys dialled to get in? What will be the worst case number of digits dialled? Can you prove that this it the theoretically best, that no other algorithm will provide a lower worst case?

What will be the average across all possible entry codes? Can you prove that your algorithm provides the minimal number of total keypresses in the average case?

I do not have any ready-made "right answer" to this problem, just a bunch of implementations of how to make sure I get it if I have forgotten the code with no complexity analysis. I do know the code, so I do get in - don't worry about that! The problem here is not to get in, but the complexity of getting in if you do NOT know the code!

To insert a node at the back of a XOR doubly linked list

Tarun Jha — Thu, 17 Oct 2019 19:38:00 GMT

here is the method to insert a node at the front in the XORed doubly linked list or also known as memory efficient doubly linked list :

C++

// To write a memory efficient linked list
#include <iostream>
using namespace std;

// Node structure of a memory efficient doubly linked list
class Node {
public:
    int data;
    Node *npx;      //  XOR of next and previous node
};

// return XORed value of the node address
Node *XOR(Node *a, Node *b){
    return ((Node *)( (uintptr_t)(a) ^ (uintptr_t)(b) ));
}

// insert a node at the beggining of the XORed linked list and makes the newly inserted node as head
void insert(Node **head_ref, int data){
    // allocate memory for new node
    Node *new_node = new Node();
    new_node->data = data;

    // since node is inserted at the beggining, npx of the new node will always be XOR of curent head and null
    new_node->npx = XOR((*head_ref), nullptr);

    // if the linked list is not empty, then npx of current head node will be XOR of new node and node next to current head
    if(*head_ref != nullptr){
        // (*head_ref)->npx is XOR of null and next.
        // so if we do XOR of it with null, we get next
        Node *next = XOR((*head_ref)->npx, nullptr);
        (*head_ref)->npx = XOR(new_node, next);
    }

    // change head
    *head_ref = new_node;
}

// prints contents of doubly linked list in forward direction
void printList(Node *head){
    Node *curr = head, *prev = nullptr, *next;

    cout << "Following are the nodes of Linked List: \n";

    while(curr != nullptr) {
        // print current node
        cout << curr->data << " ";

        // get the address of next node : curr->npa is next^prev,
        // so curr->npx^prev will be next^prev^prev which is next
        next = XOR(prev, curr->npx);

        // update prev and curr for next iteration
        prev = curr;
        curr = next;
    }
}

// Driver function
int main(){
    Node *head = nullptr;
    insert(&head, 10);
    insert(&head, 20);
    insert(&head, 30);
    insert(&head, 40);
    insert(&head, 50);
    insert(&head, 60);

    printList(head);

    return 0;
}

Here is the code i have tried to put an element at the back of the list:

C++

Node *insert(Node **last, int data){
    // allocate memory for new node
    Node *new_node = new Node();
    new_node->data = data;

	new_node->npx = XOR(*last, nullptr);

	if(*last != nullptr) {
		Node *prev = XOR((*last)->npx, nullptr);
		(*last)->npx = XOR(prev, new_node);
	}

	// *last = new_node;
	return (new_node);
}

// Driver function
int main(){
    Node *head = nullptr;
    head = insert(&head, 10);
    head = insert(&head, 20);
    head = insert(&head, 30);
    head = insert(&head, 40);
    head = insert(&head, 50);
    head = insert(&head, 60);

    printList(head);

    return 0;
}

But it is not working
output: it is same in both the cases

Thank you

Why non-template function does not compile where as template function compiles?

PBMBJoshi — Fri, 03 May 2019 09:23:00 GMT

I am trying to call two identical functions (one is templated and the other one is normal). The templated one compiles successfully, but the non-templated one gives compilation error. Why?

template <typename ParamType>
void Template_universal_ref(ParamType&& param)
{
    cout << "Template_universal_ref, param : " << param << endl;
}

void NonTemplate_universal_ref(int&& param)
{
    cout << "NonTemplate_universal_ref, param : " << param << endl;
}

int main()
{
    int x=5;
    Template_universal_ref(x);
    //NonTemplate_universal_ref(x); // This is giving compilation error
    return 0
}

In my view

NonTemplate_universal_ref(x);

is special version of

Template_universal_ref(x);

. Why does NonTemplate_universal_ref(x); result in compilation error?

Advice on interdependent asynchronous functions and task queuing?

arnold_w — Fri, 08 Feb 2019 10:07:00 GMT

I am working with embedded programming in standard C and there are 2 microcontrollers communicating with each other using a home-made SPI-protocol. In addition, microcontroller 2 has a CAN-bus that should also (indirectly) be fully accessible from microcontroller 1. The scheduler and task queues are also home-made so no realtime operating system is used. My tasks look like this:

C++

void (*task_t)(uint8_t* taskData, uint16_t sizeOfTaskDataInBytes);

My functions to add 1 or 2 tasks look like this:

C++

typedef enum {
    TASK_IN_WAIT_PHASE      = 0,
    TASK_FINISHED           = 1
} taskStatus_e;

typedef taskStatus_e (*getTaskStatusCallback_t)(uint8_t* data, uint16_t dataSizeBytes);

Bool_t queueTask(taskQueueSelector_e, task_t, uint8_t* data, uint16_t dataSizeBytes, getTaskStatusCallback_t);
Bool_t queue2Tasks(taskQueueSelector_e, task_t task1, uint8_t* data1, uint16_t data1SizeBytes, getTaskStatusCallback_t getTaskStatusCallback1, task_t task2, uint8_t* data2, uint16_t data2SizeBytes, getTaskStatusCallback_t getTaskStatusCallback2);

When microcontroller 1 wants to read from microcontroller 2 over SPI, the following code is used:

C++

struct SPI_secretData_s {
    volatile Bool_t                    accessInProgress;
    volatile int8_t                    numRetriesLeft;
};

#define PLEASE_SEE_NUM_REGS_TO_ACCESS_PARAMETER     (1)

struct SPI_readRegsTaskParams_s {
    struct SPI_secretData_s            secretData;
    volatile uint32_t                  startAddr;
    volatile uint16_t                  numRegsToAccess;
    volatile SPI_readStatus_e          readStatus;
    volatile uint16_t                  readBuffer[PLEASE_SEE_NUM_REGS_TO_ACCESS_PARAMETER];
};

queue2Tasks(SPI_QUEUE_SELECTOR, SPI_readRegs, (uint8_t*)&SPI_readRegsTaskParams, sizeof(SPI_readRegsTaskParams), SPI_getTaskStatusCallback, SPI_handleReadIsFinished, NULL, 0, NULL);

taskStatus_e SPI_getTaskStatusCallback(uint8_t* data, uint16_t dataSizeBytes) {
    struct SPI_readRegsTaskParams_s* SPI_readRegsTaskParams = (struct SPI_readRegsTaskParams_s*)data;
    return (SPI_readRegsTaskParams->secretData.accessInProgress) ? TASK_IN_WAIT_PHASE : TASK_FINISHED;
}

uint32_t SPI_handleReadIsFinished(uint8_t* notUsed, uint16_t sizeOfNotUsedInBytes) {
    struct SPI_readRegsTaskParams_s* SPI_readRegsTaskParams = (struct SPI_readRegsTaskParams_s*)getPreviousTaskData();
    //... Do what you need to do with the read data...
}

When microcontroller 2 wants to read from the CAN-bus, the following code is used:

C++

struct CAN_secretData_s {
    volatile Bool_t                         accessInProgress;
};

struct CAN_readRegsTaskParams_s {
             struct CAN_secretData_s        secretData;
    volatile uint32_t                       startAddr;
    volatile uint8_t                        numRegsToReadMax4;
    volatile uint16_t                       readRegsBuffer[4];
    volatile CAN_readStatus_e               readStatus;
};

queue2Tasks(CAN_QUEUE_SELECTOR, CAN_readRegs, (uint8_t*)&CAN_readRegsTaskParams, sizeof(CAN_readRegsTaskParams), CAN_getTaskStatusCallback, CAN_handleReadIsFinished, NULL, 0, NULL);

taskStatus_e CAN_getTaskStatusCallback(uint8_t* data, uint16_t dataSizeBytes) {
    struct CAN_readRegsTaskParams_s* CAN_readRegsTaskParams = (struct CAN_readRegsTaskParams_s*)data;
    return (CAN_readRegsTaskParams->secretData.accessInProgress) ? TASK_IN_WAIT_PHASE : TASK_FINISHED;

uint32_t CAN_handleReadIsFinished(uint8_t* notUsed, uint16_t sizeOfNotUsedInBytes) {
    struct CAN_readRegsTaskParams_s* CAN_readRegsTaskParams = (struct CAN_readRegsTaskParams_s*)getPreviousTaskData();
    //... Do what you need to do with the read data...
}

Could someone please suggest how I should handle the case when microcontroller 1 wants to read from the CAN-bus, via microcontroller 2?

Recommended way to deal with queues and pointers to buffers

arnold_w — Sun, 03 Feb 2019 20:09:00 GMT

I am working with embedded programming in standard C and there are 2 microcontrollers communication with each other using a home-made protocol. The scheduler and task queues are also home-made so no realtime operating system is used. My tasks look like this:

C++

void (*task_t)(uint8_t* taskData, uint16_t sizeOfTaskDataInBytes);

My add-task-to-queue-function looks like this:

C++

Bool_t addTaskToQueue(queueSelector_e, task_t, uint8_t* taskData, uint16_t sizeOfTaskDataInBytes);

Please note that the taskData is also inserted into the queue (in an area called task data pool area) so it's not just a pointer to taskData that is being queued. The task data to write data from microcontroller 1 to microcontroller 2 needs to look something like this:

C++

struct writeRegTaskData_s {
    uint32_t startAddr;
    uint16_t numRegsToWrite;
    uint8_t dataToWrite[numRegsToWrite]; // When I want the data to be put inside the queue as well
or
    uint8_t* dataToWrite // When I have a big static buffer that I don't want to put inside the queue
}

The problem is with the dataToWrite parameter. Sometimes a lot of data will be written, for example, during a firmware upgrade, and then it's overkill to put all the dataToWrite into the queue, it's perfectly fine to have one static buffer. At other times, for example when reacting to different push button events, I want to put my dataToWrite on the stack and then add it into my task queue. However, when I do this, I must make sure dataToWrite points to the proper location inside my task queue data pool and not on the original buffer on the stack. What's the recommended way to solve this issue in a clean way?

Can a union in standard C "skip" members?

arnold_w — Fri, 01 Feb 2019 09:46:00 GMT

The following is an example of a simple struct union:

C++

typedef union _UINT32_PART_ {
   uint32_t dwWord;

   struct {
      uint16_t dwMSB;
      uint16_t dwLSB;
   } hw;

   struct {
      uint8_t byMSB;
      uint8_t byMSBL;
      uint8_t byLSBH;
      uint8_t byLSB;
   } b;
} DWORD_PART;

Is is possible to somehow omit, for example dwMSB and byLSBH, without making the subsequent members point to the wrong things? So, basically this is what I want:

C++

typedef union _UINT32_PART_ {
   uint32_t dwWord;

   struct {
                         // 2 bytes empty gap
      uint16_t dwLSB;    // This must still point to the 2nd word, not the 1st!
   } hw;

   struct {
      uint8_t byMSB;
      uint8_t byMSBL;
                         // 1 byte empty gap
      uint8_t byLSB;     // This must still point to the 4th byte, not the 3rd!
   } b;
} DWORD_PART;

Which type of Regex best to learn for programming with C?

HS_C_Student — Mon, 17 Dec 2018 14:43:00 GMT

I like C but I feel it's Achilles heel is string processing. I've started to do a lot of parsing of text databases in arbitrary format without documentation lately and I need to adapt.

What I need to do is define patterns - expected format for the data and to store the values only if the whole string matches that known pattern. Input validation.

I'd rather not run the rest of my code without verifying the input conforms.

I think regular expressions are the best way to augment my existing skills without learning a new language, but regexes seem kind of varied and mixed breed.

Perl (5?) Seems to have formal standardization of regexes which is supported in many searching and text editing programs. There's also PCRE which I can compile on windows or download precompiled lib/dll.

Should I learn Perl regexes and use PCRE or am I overlooking things?

Directory manipulation in C++

tasumisra — Tue, 16 Oct 2018 14:26:00 GMT

Dear Friends,

I am working on a legacy project where i do not have support for boost libraries or latest C++ version.

I need to identify the path of a file with given extension(*.abc) that is inside couple of folder.

as example i have path like C:\test

but the given file is found in c:\test\Application\SomeohterApplication\hello.abc

can someone help please ?

Thanks in advance.

vikas da

Microsoft Office Object Library

JM2251 — Sun, 14 Oct 2018 15:31:00 GMT

Hi,
I am trying to use Ribbon control in my outlook addin but could not find "

Microsoft Office xx.x Object Library

in available type library.

I am using Microsoft Office 365 ProPlus. Please help.

Unable to find atlapp.h file in Visual Studio 2017

Krishna Rao Yekkali — Wed, 29 Aug 2018 10:17:00 GMT

Hi,

Freshly installed Windows 10 and VS2017 enterprise and doing migration from VS2010 to VS2017. Getting fatal error C1083: Cannot open include file: 'atlapp.h: No such file or direectory when i compile one of the project, even i have selected ATL and required options during VC2017 installation.
I would appreciate if anyone can suggest how to resolve this issue.

Thanks & Regards
Krishna Rao

CEditCtrl in FrameWnd

john5632 — Thu, 02 Aug 2018 08:24:00 GMT

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

MFC VC2015 How to build from command line both settings: Use Shared DLL and Use Static DLL

Member 10245587 — Sun, 15 Jul 2018 11:37:00 GMT

Hello boys.

I use Visual Studio 2015.
Projekt setting: Use MFC in a Shared DLL.

For building from command line is used:
msbuild .\my_project.sln /t:Rebuild /p:Configuration=Release /p:Platform=x64
All is working well, build runs OK.

I would like to ask you:
Is there a way how to switch (any parametr for msbuild) between Shared and Static MFC DLL?

for example:
msbuild .\my_project.sln /t:Rebuild /p:Configuration=Release /p:Platform=x64 /p:ANYKEYWORD=Shared
or
msbuild .\my_project.sln /t:Rebuild /p:Configuration=Release /p:Platform=x64 p:/ANYKEYWORD=Static
or anything like that.

I can not find a way, how to build project from command line and switch both possibilities: "Use MFC in a Shared DLL" and "Use MFC in a Static DLL" without opening IDE and switching it there manualy in project setting.

Thank you for advices and help.
Lubomir