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And i really do like 'M'...
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Of course. 
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C is highly portable and simple language. But, because of some limitation of C, it is loosing fame.
The main reason behind is, it doesn't support object-oriented programming features. Means-
Inheritance
Encapsulation
Polymorphism etc.
are not suported by C programming language, that's why C++ is developed.
Even C doesn't perform run time type checking.
modified 16-Apr-19 21:38pm.
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Abhays01 wrote: The main reason behind is, it doesn't support object-oriented programming features
…
Inheritance
Encapsulation
Inheritance (structs inheriting from other structs), and encapsulation (struct name in the H file, and struct implementation in the C file) are certainly possible with C.
"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
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David Crow wrote: struct name in the H file, and struct implementation in the C file
That's not encapsulation, in any sense.
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In object oriented programming languages, encapsulation is used to refer to one of two related but distinct notions, and sometimes to the combination thereof:
- A language mechanism for restricting direct access to some of the object's components.
- A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.
Opaque structs in C fit at least one of those definitions for abstraction. You could probably make the case that since you'd need to bundle the opaque struct with some subroutines to manipulate it that you're basically writing methods - the only difference is the class keyword and the lack of an implicit *this* pointer.
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But you cannot do any form of abstraction or encapsulation in C. There is no mechanism for hiding members of a struct.
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Richard MacCutchan wrote: There is no mechanism for hiding members of a struct.
Are you saying that given the H and LIB files I mentioned earlier, that you'd be able to directly access the members of the CarPrivate struct?
"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
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Sorry, I misread that. No you could not refer to the members if they are not defined in the header. But in most cases of writing pure C code this is not an issue. Both the caller and the provider need the definition of the struct in order to pass data between them.
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How about something like:
car.h
struct car; car.c
struct car
{
private:
char make[10];
char model[10];
int year;
public:
char *getMake();
char *getModel();
char *getYear();
};Direct access to the object's components has been restricted.
The data and the methods that operate on that data are bundled together.
"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
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The keywords private and public do not exist in the C language.
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Indeed (too many years away from it), but that does not change my point. If you had something like this in the H file:
struct CarPrivate;
struct Car
{
struct CarPrivate* priv;
};
extern char* GetYear(struct Car* car);And had something like this in the C file:
struct CarPrivate
{
int year;
};
int GetYear(struct Car* car)
{
return car->priv->year;
}You would not be able to access members of CarPrivate like:
void main( void )
{
struct Car* car = some_method_to_create_car();
int year = car->priv->year;
}
"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
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Putting the definition in a header file only matters if you are trying to access the struct in separate source modules; and that has nothing to do with encapsulation. And yes, of course you could do what you suggest above, but it serves little purpose since you can still access the data directly, and thus break the pseudo encapsulation. In OOP languages the data can actually be hidden from the users of the class, in C it cannot.
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Richard MacCutchan wrote: ...since you can still access the data directly...
What if the structs were compiled into a LIB file? The user of that LIB file only has access to what is in the corresponding H file, correct?
"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
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How would that work? If you have the definitions in a header that you include in your source, then you have access to all members of the struct. Whether the actual struct is allocated on the stack, the heap or via a pointer to an external piece of memory, you can still see all the members.
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Richard MacCutchan wrote: If you have the definitions in a header...
The declaration would be in the H file. The implementation/definition would be in the C file, which would get compiled into a LIB file. Thus the only thing accessible to those using the LIB file would be the declarations in the corresponding H file (which does not include anything private).
"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
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At the risk of repeating myself, that is not going to work. If you are going to do all the data manipulation in the lib file and not provide the struct definition to the user, then there is nothing required in the H file at all. But that means the user cannot allocate any space for the data in the first place.
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Richard MacCutchan wrote: At the risk of repeating myself, that is not going to work.
Please repeat, because I really want to know what I'm doing wrong.
Richard MacCutchan wrote: ...and not provide the struct definition to the user...
In the sample code that I showed, the user would have access to the definition of the Car struct (which could obviously contain more public members), and to the declaration of the CarPrivate struct. CarPrivate would be fully implemented/defined in the LIB file.
Richard MacCutchan wrote: But that means the user cannot allocate any space for the data in the first place.
Are you referring to the user doing something like:
struct Car* car = some_method_to_create_car(); Similar to the GetYear() function shown earlier, the some_method_to_create_car() function (that I didn't bother implementing) would have access to the CarPrivate members.
"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
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David Crow wrote: I really want to know what I'm doing wrong.
You are not doing anything wrong. But I think maybe you are trying to solve a problem that does not exist.
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Interesting discussion, since i have implemented similar functionality in the passed. The only thing the user had to work with was a handle and predefined functions that take the handle as an argument.
I used this method to create STL type containers. The drawback being there was no type checking, as the data stored was just a block of memory supplied by the user.
I used a similar method when creating my old DOS interface library, it would wire up the function pointers defined in the window structure at run-time. Basically all visual elements were a window; how they were wired-up depended on the function called to create them.
You cannot created protected members, but you can created hidden members. If I remember correctly, MS uses a similar method when you create a window - there is hidden data.
The following is just off the top of my head and does not represent an actual implementation.
#define EXPHANDLE void*
EXPHANDLE ExpContainer_Create(size_t data_size, size_t count);
void ExpContainerDestroy(EXPHANDLE hExpContainer);
size_t ExpContainer_Insert(EXPHANDLE hExpContainer, void*, size_t pos);
size_t ExpContainer_Append(EXPHANDLE hExpContainer, void*);
struct ExpContainer
{
size_t data_size_;
size_t size_;
size_t used_;
void* data_;
unsigned signature_;
};
EXPHANDLE ExpContainer_Create(size_t data_size, size_t count);
{
struct ExpContainer* pContainer = malloc(sizeof(struct ExpContainer));
return (EXPHANDLE)(pContainer + offsetof(signature_));
}
INTP
"Program testing can be used to show the presence of bugs, but never to show their absence." - Edsger Dijkstra
"I have never been lost, but I will admit to being confused for several weeks. " - Daniel Boone
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Yes I did the same thing.
The header file did not expose the structure. It was defined in the source file and allocated/managed by the methods. Not sure if I typedef'd a handle for the void pointer or just passed the void pointer directly.
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Aakashdata wrote: Why C is not popular among developers?
What developers are you referring to specifically? The ones here? Probably because the pool here is mainly focused on windows.
But in general it is a rather popular language and has been so for a long time.
TIOBE Index | TIOBE - The Software Quality Company[^]
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How can I retrieve the menu color for an MDI/SDI MFC app that has MFC feature pack inside ?
I mean, I have the "Application look" menu that let me choose several theme for my app, everyone having a background color, including menu. And I intend to use this color to draw some control inside app, but I don't know how to retrieve this color ... can you help me ?
I have tried with afxGlobalData and CMFCVisualManager, none of them told me what I had need ...
modified 14-Apr-19 6:20am.
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I have used a tabcontrol which should show different views for each tabs. As a trial, I have created a CView class and tried to show it for the first tab. When I select the tab, the appropriate view ( white screen view) is showing.
The problem is when I click on the view, it throws an assertion "Debug Assertion Failed at line: 252 in viewcore.CPP".
I have added the below code for selection of tabs.
if (nTab == 0)
{
CRect clientRect;
m_cTabCtrl.GetClientRect(&clientRect);
clientRect.DeflateRect(5, 18);
CTrendview *m_pNewView = new CTrendview();
// Creation of the view window
if(! m_pNewView->Create(NULL, NULL, WS_VISIBLE | WS_CHILD, clientRect,
&m_cTabCtrl, 1))
{
TRACE( "Failed view creation\n" );
}
m_pNewView->ShowWindow(SW_SHOW);
}
Please help me to find a solution for this problem.
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manoharbalu wrote:
The problem is when I click on the view, it throws an assertion "Debug Assertion Failed at line: 252 in viewcore.CPP".
And what is the code "at line: 252 in viewcore.CPP" and some lines above it?
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