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So..., start coding.
And post here specific questions when you're stuck.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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in c++ : (Account Class) Create an Account class that a bank might use to represent customers' bank accounts. Include a data member of type int to represent the account balance. Provide a constructor that receives an initial balance and uses it to initialize the data members. The constructor should validate the initial balance to ensure that it's greater than or equal to 0. If not, set the balance to 0 and display an error message indicating that the initial balance was invalid. Provide three member functions. Member function credit should add an amount to the current balance. Member function debit should withdraw money from the Account and ensure that the debit amount does not exceed the Account's balance. If it does, the balance should be left unchanged and the function should print a message indicating "Debit amount exceeded account balance." Member function getBalance should return the current balance. Create a program that creates at least two Account objects and tests the member functions of class Account.
task 1:derived two classes from Account class
one is bank albilad data members visa, points o
ther is alrajhi bank data members mastercard, points
set and get functions and chargevisa and chargemastercards.
set not exceed account balance.
charge not exceed visa or mastercards balance.
set points visa 10%, mastercards 15%. get functions
Make appropriate member functions const.
task 2:disinherite the classes
classes should share set and get function.
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...and you had question about this? What part of this don't you understand, or are having a problem with.
Just posting your homework assignment is not asking a question.
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I am trying to get ``sort(begin, end, compare)`` to work, where begin and end are iterators and compare is a boolean function. The Asset constructor is commented out because it generates an error.
I have tried to follow the example in Beginners guide to the std::sort() funct - C++ Articles[^]
This is the code:
class RDA_Names {
struct Asset { long long int asset_No = 0; string asset_Name = ""; };
struct {
bool compare(const Asset& lhs, const Asset& rhs) { return lhs.asset_No < rhs.asset_No; }
} comp;
bool compare(const Asset& x, const Asset& y);
array<Asset, 500> asset_Data;
};
bool RDA_Names::compare(const Asset& lhs, const Asset& rhs) {
return (lhs.asset_No < rhs.asset_No);
};
void RDA_Names::post_process_names() {
sort(asset_Data.begin(), asset_Data.end()) sort(asset_Data.begin(), asset_Data.end(), compare); sort(asset_Data.begin(), asset_Data.end(), comp); };
For each case, the other two cases are commented out. The format of the errors is Error number(repetition), Error text, lines within
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\ where the error was reported.
Case 1:
C2893 (5) Failed to specialize function template
\include\algorithm Lines 7361, 7419, 7423, 7434, 7447
C2672 (5) 'operator __surrogate_func': no matching overloaded function found
\include\xutility Line 1622
Case 2:
C2780 (1) 'void std::sort(const _RanIt,const _RanIt)': expects 2 arguments - 3 provided
C2672 (1) 'sort': no matching overloaded function found
C3867 (1) 'RDA_Names::compare': non-standard syntax; use '&' to create a pointer to member
Case 3:
C2064 (5) term does not evaluate to a function taking 2 arguments
\include\xutility Line 1622
\include\algorithm Lines 7419, 7423, 7434, 7447
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Case 1 fails because there's no comparison function for sort. It might work if Asset defined operator<, but I'd have to check.
EDIT: If you define bool Asset::operator<(const Asset& that), then case 1 also compiles.
Case 2 fails because compare takes a this pointer. If a comparison function is going to be part of a class, it needs to be declared static.
Case 3, I'd have to investigate. I've used this struct technique, but only for a set I believe. It's likely that array doesn't use it.
Try making your compare function a free function (outside the class) or static and see what happens in case 2. In the meantime, I'll look at this further.
* * *
Fixing case 2 looks like the way to go. I compiled the following successfully, and the constructor didn't give me any problems:
class RDA_Names {
struct Asset {
long long int asset_No = 0;
string asset_Name = "";
Asset(long long int asset, string name): asset_No(asset), asset_Name(name) {}
};
static bool compare(const Asset& x, const Asset& y);
void post_process_names();
array<Asset, 500> asset_Data;
};
bool RDA_Names::compare(const Asset& lhs, const Asset& rhs) {
return (lhs.asset_No < rhs.asset_No);
};
void RDA_Names::post_process_names() {
std::sort(asset_Data.begin(), asset_Data.end(), compare); };
modified 26-Mar-21 8:55am.
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Although it's a waste of time to say this,
And I know you've heard it before.
But your answers were most pointed
And it clearly went to the fore.
We thank you all
My wife because I don't grumble
I with nothing to grumble about.
I have tried to follow all of your suggestions (my following is full). I now have pointers or references everywhere and the thing seems to compile without complaint. Now to get rid of those damn'd nuisance run-time errors.
thanks!
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To complement what Greg was saying:
- case 3 fails because comp is a structure not a function returning a bool. Try changing it to:
bool comp (const RDA_Names::Asset& lhs, const RDA_Names::Asset& rhs)
{
return lhs.asset_No < rhs.asset_No;
}
You will have to also make Asset structure public.
As a case 4 you can try this:
sort (asset_Data.begin (), asset_Data.end (), [](auto& l, auto& r)->bool {
return l.asset_No < r.asset_No; });
where the comparison function is an anonymous lambda.
The next step is to look at how efficient your code will be. If you are sorting only 500 objects and you don't do it too often, it's probably OK. In general however your solution is highly inefficient. Every time sort has to exchange two elements it makes copies of the asset_Name string.
There are various ways to improve it:
- keep a unique_ptr pointer to string and provide a move constructor for the Asset structure.
- create an array of indexes in RDA_Names and sort it inseted of sorting the asset_Data array.
Mircea
modified 26-Mar-21 9:14am.
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Your first point is right on, and gets me back to Case 2. You're second point is incorrect. What is being sorted is an object of some type. The sort routine ignores the type and whether the object containing the type is private or public. It only works on comparison, I assume signed char comparison if there is no comparison function, and the ability to index and swap. The comparison function has no cognizance of privacy, it is only passed pointers/objects and returns a bool.
At the sort base level, the input object need not be public, and if the input object contains objects, these contained objects need not be public.
Just guessing.
thanks
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Quote: Just guessing.
Well, you didn't guess right 
Pretty much all you said is valid for the old C qsort function. std::sort is an entirely different beast. I suggest you carefully read the description at std::sort - cppreference.com[^]
Quote: The sort routine ignores the type and whether the object containing the type is private or public.
I'm not sure I understand what you mean by "the object containing the type". In C++ objects don't contain types. Besides the sort routine is not ignoring the object type at all. According to C++ reference: "The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible". That requires at least a copy constructor for the object (either user defined or generated by the compiler).
Quote: The comparison function has no cognizance of privacy, it is only passed pointers/objects and returns a bool.
Of course not, the comparison function needs to access the members of the object in order to compare them. Either it is a member function or a friend function or the members in question are public.
The example on the C++ reference page mentioned above shows all the different methods you can use to invoke the std::sort algorithm.
Mircea
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My knowledge of the low level implementation of C++ structures and classes is limited.
But I want to ask someone who might know, is it theoretically possible to derive a class from a Win32 structure and add methods and still be able to pass the new "structure" to a Win32 API?
I do know that adding class data members would be out of the question, because that would change the size of the structure.
But is adding methods to a structure something I could do and still use it in the windows api?
The difficult we do right away...
...the impossible takes slightly longer.
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Yes, it is very much possible. You can write something like this:
class MyPen : public LOGPEN {
public:
MyPen ();
void use_pen ();
private:
int stuff;
}
MyPen the_pen;
HPEN hp = CreatePenIndirect ((LOGPEN*)&the_pen);
Note that you can also extend your object with additional data members. They will be placed after the base class (Windows structure) and they will do no harm.
Mircea
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Thanks for your reply. I'm excited to try this.
Your example is great. But if I wanted to use an array of MyPen's then that would surely cause problems because of the larger size, no?
The difficult we do right away...
...the impossible takes slightly longer.
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Correct but only if the Windows API call takes an array of (the smaller) structures as parameters. Of top of my head, I cannot think of one that does.
Mircea
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This is the way some MFC classes are implemented:
typedef struct tagPOINT
{
LONG x;
LONG y;
} POINT, *PPOINT, NEAR *NPPOINT, FAR *LPPOINT;
class CPoint :
public tagPOINT
{
...
};
No additional members and virtual functions to get binary compatibility with underlying structure.
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Hi, thanks very much for your post.
Do I understand correctly that non-virtual functions would ruin binary compatibility?
The difficult we do right away...
...the impossible takes slightly longer.
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Non-virtual functions don't change a class instance size. You can use this technique, as in existing Microsoft classes like CPoint, CRect, adding instance non-virtual functions and static functions, if necessary.
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Hello,
I am displaying an image in a static control (in a dialog) and trying to stretch according to the zoom factor on mouse position. Zoom on mouse position is working fine, but the image is not fitting inside the static control, going all over the dialog.
Below is the code.
Gdiplus::Bitmap *gpBitmap = new Gdiplus::Bitmap(mImagePath);
int origW = gpBitmap->GetWidth(); int origH = gpBitmap->GetHeight();
RECT rcVPC;
GetClientRect(hWnd, &rcVPC); HDC hDc = GetDC(hWnd);
float perW = (float)rcVPC.right / (float)origW;
float perH = (float)rcVPC.bottom / (float)origH;
int newW = origW * perW * mVPZoomFactor; int newH = origH * perH * mVPZoomFactor;
Gdiplus::Bitmap *bmpResized = new Gdiplus::Bitmap(newW, newH, gpBitmap->GetPixelFormat());
Gdiplus::Graphics *graphics = new Gdiplus::Graphics(bmpResized);
graphics->DrawImage(gpBitmap, 0, 0, newW, newH);
int zoomWidth = (int)(0.5 + newW * mVPZoomFactor);
int zoomHeight = (int)(0.5 + newH * mVPZoomFactor);
double dXFactor = (double)rcVPC.right / stX; double dYFactor = (double)rcVPC.bottom / stY;
int left = stX - zoomWidth / dXFactor;
int right = stY - zoomHeight / dYFactor;
HBRUSH hB = GetSysColorBrush(COLOR_3DDKSHADOW);
FillRect(hDc, &rcVPC, hB);
HDC hdcMem = CreateCompatibleDC(hDc);
bmpResized->GetHBITMAP(0, &hBmpVPCanvas);
HBITMAP oldBmp = (HBITMAP)SelectObject(hdcMem, hBmpVPCanvas);
StretchBlt(hDc, left, right, zoomWidth, zoomHeight, hdcMem, 0, 0, newW, newH, SRCCOPY);
SelectObject(hdcMem, oldBmp);
DeleteDC(hdcMem);
delete gpBitmap;
Can anyone help me, what i am doing wrong?
Regards,
Gopinath.
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Gopi Nath wrote: what i am doing wrong?
Probably mixing GDI and GDI+; you should only use one of these, preferably GDI+. Zooming an image is quite simple in GDI+ as you just need to specify the target rectangle's position and size.
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Thank you Richard, tried with GDI+ only with some changes, now, i am able to get the required output.
Regards,
Gopinath.
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I'm working on an embedded ARM-project (STM32F) and I'm programming in C programming language and compiling with Eclipse/GCC. In the project there is TRACE functionality implemented that, if enabled, logs various things over UART using queues and DMA:
#define TRACE(grp, lvl, ...) traceToPrintStream(grp, __FILE__, __FUNCTION__, __LINE__, lvl, __VA_ARGS__) It can be used, e.g. like this:
TRACE("regCallbacks", T_D, "The user pressed the button");
TRACE("regCallbacks", T_D, "Write to reg %d. First written byte: 0x%X", regAddr, regValues[0]);I need a different trace that is not queued, does not use DMA and does not include the file name, function name and line number, but the other persons in this project do not agree to throw out the existing TRACE, so I need to make something in parallel. I want to be able to enable my TRACE in two ways, either by #defines:
#define ENABLE_USER_EVENTS_LOGGING
#define ENABLE_COMMUNICATOIN_BUS_LOGGING or by setting a varible during runtime:
Bool_t enableCommunicationBusLogging;
Bool_t enableUserEventsLogging; I need a different grouping (the grp parameter) than the others, so the example TRACEings above would have to be augmented with my grouping as well:
TRACE_EX("regCallbacks", USER_EVENTS, T_D, "The user pressed the button");
TRACE_EX("regCallbacks", COMMUNICATION_BUS, T_D, "Write to reg %d. First written byte: 0x%X", regAddr, regValues[0]);The rules I would like to apply are:
1. If my TRACE is enabled using the macros (hardcode enabled), then the other TRACE can not be used (hardcode disabled).
2. If my TRACE is not enabled using the macros, then both TRACEs can be enabled/disabled during runtime independently of each other. However, they are enabled per groups!
Does anybody know how I can solve this? I found a great website (C Preprocessor tricks, tips, and idioms · pfultz2/Cloak Wiki · GitHub[^]) that shows some really neat macro-tricks, but I'm not sure how to apply it my case.
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As I understand it (assuming the traceToPrintStream function is fixed) you need a slightly different macro for your TRACE_EX, something like:
#define TRACE_EX(grp, lvl, ...) traceToPrintStream(grp, "", "", 0, lvl, __VA_ARGS__)
If you want to enable the traces at runtime then you need them always enabled at compile time, otherwise you will need to rebuild the code every time. So to allow the traces to be based on switches you need something like:
#define TRACE_EX(switch, grp, lvl, ...) \
if (switch) \
{ \
traceToPrintStream(grp, "", "", 0, lvl, __VA_ARGS) \
}
where switch is the name of the boolean that controls the tracing.
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Ok, so this is what I have now:
#define USER_EVENTS_LOGGING 0x00000001
#define COMMUNICATOIN_BUS_LOGGING 0x00000002
uint32_t enabledMyGrpBitFlags = 0;
#if defined(ENABLE_USER_EVENTS_LOGGING)
#define TRACE_EX(grp, myGrp, lvl, ...) if (myGrp & USER_EVENTS_LOGGING) printf_(__VA_ARGS__)
#elif defined(ENABLE_COMMUNICATOIN_BUS_LOGGING)
#define TRACE_EX(grp, myGrp, lvl, ...) if (myGrp & COMMUNICATOIN_BUS_LOGGING) printf_(__VA_ARGS__)
#else
#define TRACE_EX(grp, myGrp, lvl, ...) \
do { \
if (myGrp & enabledMyGrpBitFlags) { \
printf_(__VA_ARGS__); \
} \
traceToPrintStream(grp, __FILE__, __FUNCTION__, __LINE__, lvl, __VA_ARGS__); \
} while (0)
#endifIs it possible to remove the run-time checks:
if (myGrp & USER_EVENTS_LOGGING)
if (myGrp & COMMUNICATOIN_BUS_LOGGING) so that the TRACE_EX macro would become empty when the myGrop isn't matching? In other words, let's say only ENABLE_USER_EVENTS_LOGGING (not ENABLE_COMMUNICATOIN_BUS_LOGGING) is defined, then I would like the following line to "disappear" after the preprocessor is finished:
TRACE_EX("regCallbacks", COMMUNICATION_BUS, T_D, "Write to reg %d. First written byte: 0x%X", regAddr, regValues[0]);Is that possible somehow?
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The run time checks are only effective at the time the code runs, so there is no way that the macro can be changed at that point. And the macro itself is evaluated, and its code generated in the preprocessor, long before the code is running.
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I want to be able to compile in 2 different modes:
1. Normal mode: The 2 types of TRACE can be enabled/disabled during runtime independently of each other.
2. Hardcoded my TRACE only mode: Only my TRACE is enabled (1 or more myGrp TRACE groups), it's impossible to enable/disable anything TRACE related during runtime.
So, when compiling in mode 2 above, it should be possible for the macro to evaluate the passed myGrp parameter to determine how the TRACE_EX should be expanded. So if we only enable
#define ENABLE_USER_EVENTS_LOGGING then the preprocessor should be able to determine that this line should be removed:
TRACE_EX("regCallbacks", COMMUNICATION_BUS, T_D, "Write to reg %d. First written byte: 0x%X", regAddr, regValues[0]);
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I have tried what I think you are asking for but the preprocessor rejects it. As far as I know you can only do it the way I already suggested.
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