C / C++ / MFC

7-Oct-22 21:35

Try breaking it down into its constituent parts:

mark is an array of 5 elements.
Each element is a vector.
And each element of the vector is also a vector.
And each element of the inner vectors is an integer.

As it stands though, the array is null, so you need to initialise each of its elements with a new vector. You then need to decide what actual information you want to store in the vectors.

Style question

Mircea Neacsu3-Oct-22 15:33

3-Oct-22 15:33

I have a C++ function that takes as argument an iterator and needs to increment it without passing the end of the container. I can write it as:
variant A:

C++

bool func (std::string::iterator& ptr, std::string& container)
{
  //...
  if (ptr != container.end())
    //do stuff
}

and call it as:

C++

func (s.begin(), s);

or I could write it as
variant B:

C++

bool func (std::string::interator& ptr, std::string::const_iterator& limit)
{
  //...
  if (ptr != limit)
    //do stuff
}

and call it as:

C++

func (s.begin(), s.end());

(the example assumes the container is a string but that's not important)

Which one would you favor?

Mircea

Graham Breach3-Oct-22 21:23

Graham Breach

3-Oct-22 21:23

If the function modified the contents of the container I would probably pass it the container reference, otherwise I would prefer the iterators (or even a std::span).

Mircea Neacsu4-Oct-22 2:27

4-Oct-22 2:27

Good points, thank you! However std::span is C++20 and I want to keep the code C++14.

Mircea

CPallini3-Oct-22 23:47

CPallini

3-Oct-22 23:47

The second one: give to the function the strict necessary for its task.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Mircea Neacsu4-Oct-22 2:28

4-Oct-22 2:28

Yep, my thoughts exactly. Thank you!

Mircea

CPallini7-Oct-22 1:35

CPallini

7-Oct-22 1:35

"great minds..."
Laugh | :laugh:

You are welcome.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

BernardIE53177-Oct-22 3:14

BernardIE5317

7-Oct-22 3:14

I have a more or less strict rule i.e. to wit in particular to be specific namely things that act like pointers are passed via copy constructor not via reference since raw pointers are fundamental type objects so take up little space and a reference is a pointer anyway. I agree w/ the chap who suggested passing only what the function requires i.e. first, last iterators. Further at point of call the code is easier to understand its purpose as it passes only what the function requires also it just looks better and is easier to understand as fewer ideas/concepts are involved namely the one idea/concept "iterator" rather than the two ideas/concepts "iterator and container". Was there not a recent article in a recent CP newsletter discussing this very thing i.e. minimizing the number of ideas/concepts needed to understand any code?

Mircea Neacsu7-Oct-22 3:18

7-Oct-22 3:18

meagreProgrammer wrote:
things that act like pointers are passed via copy constructor not via reference

Except that in my case the iterator needs to be changed by the function, hence I have to pass a reference.

Mircea

BernardIE53177-Oct-22 3:27

BernardIE5317

7-Oct-22 3:27

Would it be too lengthy or tedious an explanation to explain the need to modify the iterator. I find such a need quite unusual and do not recall ever having to perform same.

Mircea Neacsu7-Oct-22 3:40

'System': a namespace with this name does not exist

7-Oct-22 3:40

No problem: the iterator is a pointer in a UTF-8 encoded string and the function (called next) has to advance to the next code point (1, 2, 3 or 4 char). If iterator is at end of string it doesn't advance.

Although a very simple function, I had a number of design decisions to make:
- How should I deal with improperly encoded UTF-8 strings? I decided to return false if the string is not properly encoded.
- Should I just leave out the boundary check and just document it? I decided against as it would have been unsafe.

And the last one I was asking about: For limit check, should I just pass the string or the end iterator.

Mircea

Kevin Marois3-Oct-22 6:12

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:12

I am NOT a C++ guy, so bear with me.

I am working on a C#/WPF app that references two C++ projects.

We just converted the solution from .Net Framework to .Net Core 6.0, and now the C++ projects won't compile while in the solution. If I open the C++ projects stand-alone, they compile file.

Primarily I'm getting the compile time error

'System': a namespace with this name does not exist

I've been Googling and 99% of the answers all say this. I've tried the answers and still get the same errors.

At this point I need help. I'm guessing it's some kind of configuration issue, but I really don't know.

Thanks

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard MacCutchan3-Oct-22 6:26

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:26

An error message by itself does not tell us much. What is the context, and are you sure this would not fit better in Managed C++/CLI Discussion Boards[^] ?

Kevin Marois3-Oct-22 6:30

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:30

Richard MacCutchan wrote:
What is the context

Not sure what you mean by "what is the context". Like I said, the project is in a solution with a C#/WPF project and the C++ project now doesn't compile.

Richard MacCutchan wrote:
and are you sure this would not fit better in Managed C++/CLI Discussion Boards

I have no clue. But I could move it there.

Again, I have ZERO C++ experience, so I'm really in the dark with all this.

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard MacCutchan3-Oct-22 6:39

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:39

Kevin Marois wrote:
Not sure what you mean by "what is the context"

All you have given us is an error message. We have no idea whether this is unmanaged or managed code, what the actual code that causes the error looks like &c.

Kevin Marois3-Oct-22 6:43

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:43

OK, so here's the lines of code that are failing:

using namespace System;
using namespace System::Reflection;
using namespace System::Runtime::CompilerServices;
using namespace System::Runtime::InteropServices;
using namespace System::Security::Permissions;

This error occurs in the using statements in every C++ file in the project.

It's a .Net 6 project, so I'm assuming it Managed code.

I'm not trying to be difficult, but I just don't know what I'm looking at so it's hard for me to know what to post here.

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard MacCutchan3-Oct-22 6:50

Re: 'System': a namespace with this name does not exist

3-Oct-22 6:50

OK, what you have is managed C++, AKA C++/CLI, which uses .NET. Those using statements are correct and it should build. However since you are converting from the Net Framework you probably need to look at Migrating C++/CLI projects to .NET Core and .NET 5+ - .NET Core | Microsoft Learn[^].

Kevin Marois3-Oct-22 6:51

3-Oct-22 6:51

OK thanks. I'll take a look

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

List assertation failure

ForNow2-Oct-22 15:50

2-Oct-22 15:50

Hi

I have the following

C++

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

C++

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;
	}

C++

struct blkdesc
	{
		char type;
		int blkaddr;
		int blklen;
		//	struct blkdesc* nextblkdesc;
	};

I declare a list class

C++

list<tcbholder> tcbcollecter;

then a iterator

C++

list <tcbholder>::iterator tcbitrate;

I am able to initialize the main iterator

C++

tcbitrate = tcbcollecter.begin();

However when I try

C++

tcbitrate->straverse = tcbitrate->strptr.begin();

I get the following

C++

_STL_VERIFY(this->_Ptr != _Mycont->_Myhead, "cannot dereference end list iterator");

its in the list member line 151

Dont Understand

Thanks

Graham Breach2-Oct-22 21:06

Graham Breach

2-Oct-22 21:06

It means that your "tcbcollecter" list was empty when you assigned the "tcbitrate" iterator. Calling begin() on an empty list will give you the end() iterator, because there is no real element to point to. You can't dereference it because it doesn't point at anything.

ForNow2-Oct-22 21:22

2-Oct-22 21:22

How would I solve this problem would calling tcbitrate->push_back solve it after that there is something on the list though the members of tcbcollector have not been assigned values

Graham Breach2-Oct-22 21:46

Graham Breach

2-Oct-22 21:46

Instead of trying to manipulate the contents of these structs from outside I would add member functions to do it.

ForNow3-Oct-22 8:49

3-Oct-22 8:49

Was thinking how to that don’t know if it’s practical my list represents the output of VSMLIST z/os assembler mainframe macro representing the amount allocate free and I unallocated storage for an address space
It’s listed by storage blocks ( address and length ) storage descriptors representing a storage subpool which different attributes and storage keys and the TCB task control blocks of the task that own them

CPallini2-Oct-22 21:08

CPallini

2-Oct-22 21:08

Quote:
tcbitrate = tcbcollecter.begin();

Quote:
tcbitrate->straverse = tcbitrate->strptr.begin();

If tcbcollecter is empty then the complaint is correct.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

ForNow2-Oct-22 22:17