C / C++ / MFC Discussion Boards

Re: Passing an array as argument to a function

Richard MacCutchan31-Mar-20 23:02

Richard MacCutchan

31-Mar-20 23:02

Arrays of pointers are just as trivial as arrays of anything, if you understand how to address them.

fearless_ wrote:
I`m getting an `illegal indirection` error

Since we cannot see your screen we also cannot guess where that occurs. Please format your code properly and explain exactly where the error occurs.

Re: Passing an array as argument to a function

Calin Negru31-Mar-20 23:26

Calin Negru

31-Mar-20 23:26

I get illegal indirection at this spot

*ScreenLettersP_s[LetterVertexDataincrement]->position.x = i * letterwidth + ScreenLetterGroups[i].x

Re: Passing an array as argument to a function

Richard MacCutchan1-Apr-20 0:36

Richard MacCutchan

1-Apr-20 0:36

The variable ScreenLettersP_s is an array of pointers, so the reference ScreenLettersP_s[LetterVertexDataincrement] is one of the actual pointers. The leading asterisk on ScreenLettersP_s means an extra level of indirection which is not required (or valid).

Re: Passing an array as argument to a function

Calin Negru1-Apr-20 1:12

Calin Negru

1-Apr-20 1:12

so this is specific for structures only. because if I change *data[i] = i * 2; to data[i] = i * 2; in the k5054s example I will be editing the save entry rather than the save data.

Re: Passing an array as argument to a function

Richard MacCutchan1-Apr-20 1:26

Richard MacCutchan

1-Apr-20 1:26

No. Pointers are pointers whatever they point at, be it an array or a structure. Think about a piece of memory as a sequence of cells. So a pointer to any cell allows you to access all the following cells in order, by using an index (pointer plus offset). If you (the programmer) have decided that the area you point to should be treated as if it contains different sized blocks (aka a structure), that does not affect the physical properties of the memory. It merely allows the compiler to calculate the distance between the elements of the structure. And an array of pointers is much the same thing.

If you have trouble visualising multi levels of indirection, then always go for a single level. If you have an array of pointers, then create a temporary one and allocate an array entry to it like:

C++

CUSTOMVERTEX ** ScreenLettersP_s = new CUSTOMVERTEX* [NumberOfTextBuffers]; // an array of struct pointers
CUSTOMVERTEX* pTemp = ScreenLettersP_s[0]; // get the first pointer in the array
pTemp-> // now access the struct items.

Re: Passing an array as argument to a function

Calin Negru1-Apr-20 1:49

Calin Negru

1-Apr-20 1:49

I understand. for the record that`s directx 9.

Re: Passing an array as argument to a function

Richard MacCutchan1-Apr-20 2:45

Richard MacCutchan

1-Apr-20 2:45

fearless_ wrote:
directx 9

I have not used DirectX, but I have used plenty of other Windows' functions that use structures, arrays of structures, and even arrays of structures that contain other unstructured structures. In the latter case, the presence or absence of certain items depends on settings elsewhere.

Re: Passing an array as argument to a function

Calin Negru1-Apr-20 5:19

Calin Negru

1-Apr-20 5:19

You have a vast experience, I appreciate all your help.

Re: Passing an array as argument to a function

Richard MacCutchan1-Apr-20 6:39

Richard MacCutchan

1-Apr-20 6:39

fearless_ wrote:
You have a vast experience

~Far from it, what I don't know would fill many books.

But given that I know some stuff, I am happy to help.

Re: Passing an array as argument to a function

Calin Negru31-Mar-20 4:42

Calin Negru

31-Mar-20 4:42

So is this pointer a save of the physical address of the real thing or just an artifice done by the compiler which matches the data behind the scenes to achieve the desired result?

Re: Passing an array as argument to a function

Richard MacCutchan31-Mar-20 4:58

Richard MacCutchan

31-Mar-20 4:58

It is the actual address in the pointer. In that way you can address any array, or any structure just by passing the real address to the function.

C++

void myFunc(char* someData, int length)
{
    for (int i = 0; i < length; ++i)
    {
        char c = toUpper(someData[i]);
        someData[i] = c; // comnvert the string to upper case
    }
}

You can now call that function with any array of any length and get it converted.
In every case the function receives the physical address of the array and accesses each
character by using the index value i, where 0 <= i < length.

Re: Passing an array as argument to a function

Calin Negru31-Mar-20 5:28

Calin Negru

31-Mar-20 5:28

thank you Richard

Re: Passing an array as argument to a function

Stefan_Lang30-Mar-20 23:18

Stefan_Lang

30-Mar-20 23:18

You can do either of these, depending on what you want to do:

C++

// pass read only array of ints
void process_Carray(int const* values, int n_values);
template <int size> // caution: this will create a separate function for each array size!
void process_C11array(std::array<int,size> const& values);
void process_vector(std::vector<int> const& values);
// pass read/write array of ints
void process_Carray(int* values, int n_values);
template <int size> // caution: this will create a separate function for each array size!
void process_C11array(std::array<int,size>& values);
void process_vector(std::vector<int>& values);

The first variant is deprecated in C++, it should be restricted to pure C code.
The second variant is useful if you know the size of your arrays at compile time (and it's always the same)
The third variant is the most flexible as you don't need to know the array size, and you can even add more values within your function if you desire.

GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)

Re: Passing an array as argument to a function

Calin Negru31-Mar-20 0:02

Calin Negru

31-Mar-20 0:02

thanks, I also understand `defensive programming` now.

Re: Passing an array as argument to a function

Calin Negru11-Apr-20 5:13

Calin Negru

11-Apr-20 5:13

Just as a conclusion to everything that has been said in this thread, if you want to pass an array as argument you have to declare it as pointer in the function definition.

Re: Passing an array as argument to a function

kalberts11-Apr-20 8:19

kalberts

11-Apr-20 8:19

How could you not?

A C "array" IS a pointer to the start of it. There is nothing more to it.

Stop thinking of C as a high level language. It is a CPU independent assembly language.

Error in BSTR TagVariant After project Migration from VS2010 to VS2017

Member 1326109427-Mar-20 2:19

Member 13261094

27-Mar-20 2:19

Error in line :

CString sURL = URL->bstrVal;

//bstrVal is BSTR TagVariant

Error is

error C2440: 'initializing': cannot convert from 'BSTR' to 'ATL::CStringT<char,strtraitmfc_dll<char,atl::chtraitscrt<_chartype>>>'
1> with
1> [
1> _CharType=char
1> ]
1>note: Constructor for class 'ATL::CStringT<char,strtraitmfc_dll<char,atl::chtraitscrt<_chartype>>>' is declared 'explicit'
1> with
1> [
1> _CharType=char
1> ]

Re: Error in BSTR TagVariant After project Migration from VS2010 to VS2017

Victor Nijegorodov27-Mar-20 2:39

Victor Nijegorodov

27-Mar-20 2:39

try

CString sURL = (LPCTSTR)(_bstr_t)URL->bstrVal;

Re: Error in BSTR TagVariant After project Migration from VS2010 to VS2017

CPallini27-Mar-20 3:38

CPallini

27-Mar-20 3:38

Did you preserve the project Character Set value in the migration process?

Quote:
_CharType=char

is an hint a "Not Set" or "Use Multi-Byte Character Set" is selected, while "Use Unicode Character Set" would be possiby more appropriate.

fatal error LNK1104: cannot open file 'errorStruct.lib' Getting error while compiling application

Member 1326109427-Mar-20 2:12

Member 13261094

27-Mar-20 2:12

Migrated application from VS2010 to VS2017.

application is looking for

errorStruct.lib

file.. and it is not available on my system.

Is this VS2017 file which is missing?

Guide me on this.

Re: fatal error LNK1104: cannot open file 'errorStruct.lib' Getting error while compiling application

Richard MacCutchan27-Mar-20 3:03

Richard MacCutchan

27-Mar-20 3:03

Check your project to see where it is being referenced from.

implicitly deleted because a base class invokes a deleted or inaccessible function 'CDialog::CDialog(const CDialog &)'

Member 1326109426-Mar-20 22:15

Member 13261094

26-Mar-20 22:15

Code is here 
// CSiBatchJobMigrationDlg dialog

CSiBatchJobMigrationDlg::CSiBatchJobMigrationDlg(CWnd* pParent /*=NULL*/)
	: CDialog(CSiBatchJobMigrationDlg::IDD, pParent)
{
	//{{AFX_DATA_INIT(CSiBatchJobMigrationDlg)
	m_sDatabase = _T("");
	m_leaveDevRow = TRUE;
	//}}AFX_DATA_INIT
	// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
	m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
	m_pMenu = new CMenu;
}



Giving me error in  below line

	SiBatchJobUpdateDlg updateDlg = SiBatchJobUpdateDlg(this);

Code was working fine in VS2010 but getting this error after migration from vs2010 to vs2017

Re: implicitly deleted because a base class invokes a deleted or inaccessible function 'CDialog::CDialog(const CDialog &)'

Stephane Capo26-Mar-20 22:50

Stephane Capo

26-Mar-20 22:50

Hello,

I suppose that this should be better :

SiBatchJobUpdateDlg updateDlg(this);

Re: implicitly deleted because a base class invokes a deleted or inaccessible function 'CDialog::CDialog(const CDialog &)'

Member 1326109426-Mar-20 23:26

Member 13261094

26-Mar-20 23:26

Thanks you !!!

How to solve the problem with a simple algorithm?

tianzhili439925-Mar-20 23:25

tianzhili4399

25-Mar-20 23:25

There are a total of P levels. For any level p, there are Jp nodes. Any two nodes on the same level are not connected. And the unidirectional path weight between any two nodes Ai and Bj is D(i,j).
What is the shortest distance required from the first layer to the Pth layer?
(** Note that P is generally large and it is not recommended to traverse all possible situations **)
If this problem is abstracted as a graph, then what is actually required is the shortest path from the first layer to the last layer of a fully connected network.

What I have tried:
Use deep search, Dijkstra algorithm, Floydw algorithm, etc. to search the shortest path from all J1 nodes in the first layer to the last layer in turn, and select the minimum value from the J1 values.
What I want to know is if there is a simpler algorithm to solve this problem?

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