C / C++ / MFC

Re: 'get_osfhandle': identifier not found

20-Apr-20 1:37

Microsoft have helpfully changed the name, it is now _get_osfhandle (with a leading underscore), as defined in io.h.

leon de boer20-Apr-20 3:05

leon de boer

20-Apr-20 3:05

There are very clear and compelling reasons they had to do it when they embedded linux in the windows API via WSL2. Windows then effectively has both the linux and windows functions available and it needs to know which you are wanting to call which is down to what app you are compiling a linux one or a windows one.
Compatibility | Microsoft Docs[^]

If you aren't aware of WSL2 in Windows 10 it's time to meet to meet it Smile | :)

Trying the New WSL 2. It's Fast! (Windows Subsystem for Linux) ― Scotch.io[^]

In vino veritas

Re: 'get_osfhandle': identifier not found

Richard MacCutchan20-Apr-20 4:28

SOLVED Passing function with parameters as parameter

20-Apr-20 4:28

Yes, I was well aware of that. I have been using WSL for some time, but maybe I should upgrade to WSL2. Thanks for the link.

Vaclav_18-Apr-20 9:38

18-Apr-20 9:38

Since today is my day to ask stupid questions, here is another one.
I have some understanding how to pass a function as a parameter.
I can even add and use ONE parameter to such function.
I do not understand the

- syntax.

how to add more parameters.

What I am also missing is syntax on how to read / access , verify passed parameters.
I need to make a decision based on the parameter.

C++

void OpenGL_Stencil(void (*f)(int parameter));
void OpenGL_Stencil(void (*Stencil)(int parameter)) {
	Stencil(0);	// pass parameter ??

PS Take your time , my interned connection is like a yo-yo today.

modified 20-Apr-20 9:24am.

Greg Utas18-Apr-20 10:07

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18-Apr-20 10:07

To add more parameters, just extend the argument list: (int parameter1, int parameter2) and so on.

All you have at this point is a declaration and definition of the function OpenGL_Stencil. Its parameter is a function that returns void and takes one int parameter. The next step is to implement a function with that signature and pass it as an argument to OpenGL_Stencil.

void Something(int value) { /* code */ }

After which invoking OpenGL_Stencil(Something) should cause OpenGL_Stencil to invoke Something.

Vaclav_18-Apr-20 10:22

18-Apr-20 10:22

Yes, I got that far.
I need to read the passed parameter.

C++

<pre>void OpenGL_Stencil(void (*Stencil)(int parameter)) {
	
// clear all three buffers - not neccessary
	glClear(GL_STENCIL_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//enable estecil test
	glEnable(GL_STENCIL_TEST);
// turn off writing to color buffer
	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
// enable only to verify the stencil
//glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
// setup stencil function
	glStencilFunc(GL_ALWAYS, 1, 1);							// ??
// setup stencil opertion
	glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);					// ??
// ??
	glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
// get stencil
// TDOD need parameter here
//OpenGL_Unit_Circle(0);
	Stencil(0);	// works with OpenGL_Unit_Circle(0) parameter
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
//
this is where I am missing how to test the parameter 
	// switch keep area
	//Stencil->paramater == 0;
//	if (Stencil->paramater == 0)
		glStencilFunc(GL_EQUAL, 1, 1);		///keep inside circle
//	else
//		glStencilFunc(GL_NOTEQUAL, 1, 1);	 // keep all outside of stencil
//
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

C++

Greg Utas18-Apr-20 11:24

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18-Apr-20 11:24

I'm not certain what you're asking here.

Inside OpenGL_Stencil, the name of the parameter that was passed in (a function) is Stencil. If you're talking about the int parameter for Stencil, OpenGL_Stencil has to provide that itself. It isn't the parameter associated with Stencil, because that only describes Stencil's function signature and could actually be left out, the same as in a function declaration:

void OpenGL_Stencil(void (*Stencil)(int))

If OpenGL_Stencil doesn't know what value to pass to Stencil, you could provide it like this:

void OpenGL_Stencil(void (*Stencil)(int), int value)

after which you can invoke

Stencil(value)

Vaclav_18-Apr-20 11:52

18-Apr-20 11:52

May try it this way
the parameter is a function - Stencil
such function is passed with its own parameter - such in Stencil(parameter)

how do I access that parameter "value" in OpenGL_Stencil function?
I need to do

if(Stencil(parameter == x )

Greg Utas18-Apr-20 12:04

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18-Apr-20 12:04

You have to pass it as a parameter to OpenGL_Stencil, the way I described in the second half of my post.

Vaclav_19-Apr-20 6:47

19-Apr-20 6:47

OK, I think I have the concept - have passed function return value insed of being void.
Now I am still not sure about the proper syntax.
Here is my code

C++

OpenGL_Stencil_Circle_Build(parameter);         returns parameter OK

OpenGL_Stencil(OpenGL_Stencil_Circle_Build(6)); wrong syntax

And here is the error

Description	Resource	Path	Location	Type
Invalid arguments '
Candidates are:
int OpenGL_Stencil(void (*)(int))
'	A_STENCIL.cpp	/A_STENCIL/src	line 766	Semantic Error
invalid conversion from ‘int’ to ‘void (*)(int)’ [-fpermissive]	A_STENCIL.cpp	/A_STENCIL/src	line 766	C/C++ Problem

The declaration may be the issue ?
int OpenGL_Stencil(void (*f)(int parameter));

Could somebody please reply with correct syntax or help me with declaration ?

Greg Utas19-Apr-20 7:05

Robust Services Core | Software Techniques for Lemmings | Articles

19-Apr-20 7:05

I believe that this

invalid conversion from ‘int’ to ‘void (*)(int)

means that you are passing an int argument when a function argument is expected, specifically a function that takes one int parameter and returns void.

The problem appears to be

C++

OpenGL_Stencil(OpenGL_Stencil_Circle_Build(6))

where, based on previous posts in this thread, I assume you want OpenGL_Stencil to call OpenGL_Stencil_Circle_Build with a value of 6. If that's the case, you did not read my previous post very carefully, because you need to do it as follows:

OpenGL_Stencil(OpenGL_Stencil_Circle_Build, 6)

where OpenGL_Stencil is defined as

C++

void OpenGL_Stencil(void (*func) (int), int arg)
{
   //...
   func(arg);  // this is the line that will call OpenGL_Stencil_Circle_Build with a value of 6
}

SOLVED Re: Passing function with parameters as parameter

Vaclav_19-Apr-20 10:03

19-Apr-20 10:03

It is now working, however, the mechanics are NOT what you have presented.
The initial problem was to pass a parameter to the passed function such as
Stencil(parameter); // parameter);
Now in my poor English interpretation I have
A function OpenGL_Stencil with first argument int (*Stencil)(int) and second argument int parameter
The OpenGL_Stencil returns int which is not currently used.
The first argument - function takes the second argument as a -parameter- and returns it.
The returned value is used to switch the code which follows.
That was the original task , however, I could just use the passed second argument to do the switching, without the use of the return value.
But that is just the way I like to make sure the code is actually processing the first argument - the function.

I believe my original misunderstanding was trying to pass the second argument - parameter _ as a argument to the first argument - the function.

Next task - pass multiple arguments or a pointer....

Many thanks for your help, really appreciate it.
Cheers.

Richard MacCutchan18-Apr-20 22:21

the c programming language 3rd edition - Google Search[^]

18-Apr-20 22:21

Math problem with C code

Vaclav_18-Apr-20 7:47

Re: Math problem with C code

18-Apr-20 7:47

Just FYI, this is NOT a repost.
As usual I have posted the original in WRONG pew.
However, I found another even weirder failure of simple math case and I really do not have a clue what I am doing wrong.
Are my local variable assignments incorrect ?
Is "printf" lying to me ?

Here is the entire test code

C++

#define MAX_CIRCLES 5

struct TAG_Circles {
	float radius;
	float center;
	float center_x;
	float center_y;

} REAL_Circle[MAX_CIRCLES], IMG_Circle[MAX_CIRCLES];

void OpenGL_Stencil_Circle_Build(void);
// copy last circle to stencil
void OpenGL_Stencil_Circle_Build(void) {
	//
	int index = 5;
	{
		// last circle
		float radius = IMG_circle[index].radius;
		float center_x = IMG_circle[index].center_x;
		float center_y = IMG_circle[index].center_y;
		printf("\n Last circle #%i  radius struct %f radius  %f", index,
				REAL_Circle[index].radius, radius);
		printf("\n Last circle #%i center_x  struct %f center_x  %f", index,
				REAL_Circle[index].center_x, center_x);
		printf("\n Last circle #%i center_y  struct %f center_y  %f", index,
				REAL_Circle[index].center_y, center_y);

	}
}

Here is the output

Last circle #5  radius struct 0.065789 radius  0.131579
Last circle #5 center_x  struct 0.000000 center_x  0.118421
Last circle #5 center_y  struct 0.000000 center_y  0.000000

The questions are NOT what I am trying to accomplish with the code ,
the questions are:

1. why values printed FROM struct DO NOT match assigned values ?
2. why is "radius" TWICE of the value assigned from struct?

PS
Only

radius struct 0.065789

is of correct value.

Cheers

k505418-Apr-20 8:00

k5054

18-Apr-20 8:00

Could it be because you're assigning radius from IMG_circle but printing the value of REAL_circle?

Keep Calm and Carry On

SOLVED Re: Math problem with C code

Vaclav_18-Apr-20 9:16

Re: Math problem with C code

18-Apr-20 9:16

I am not so sure how to answer this (honestly).
Maybe I should get a different hobby - like basket weaving...
For what it is worth
I started with IMG and then realized it was wrong struct, but changed only part of the code !

Richard MacCutchan18-Apr-20 8:02

Pass a struct as a function parameter or just use it as a global variable?

18-Apr-20 8:02

Vaclav_ wrote:
Here is the entire test code

As usual it is not the entire code, since none of your struct entities have been initialised with values. Please provide the values of all the variables that you are using, explain what you are trying to calculate, and why you consider the results are wrong.

Vaclav_18-Apr-20 6:23

Re: Pass a struct as a function parameter or just use it as a global variable?

18-Apr-20 6:23

Yet another one of my favourites - academic questions.
Hopefully a decent discussion will follow, but please no more RTFM.
Cheers

k505418-Apr-20 7:17

k5054

18-Apr-20 7:17

Unless you have a good, compelling argument otherwise (and there are a few), you should prefer to pass structs as parameters. If its small (e.g. something like a struct timeval), and you don't need to modify the members, its OK to pass by value. If its large, then pass by reference (pointer). If you're not going to modify the struct in the function then you should mark the reference as const.

C++

struct small_obj {
   char description[16];
   int count;
};  // size = 20 bytes

struct large_obj {
    char text[1024][1024];
    double factor[1024][1024];
}; // size = 9 MB

void f1(small_obj arg);  // OK, puts 20 bytes on the stack, f1 gets a copy
                                // of the struct. Any modifications to the struct are
                                // local ot f1

void f2(small_obj* arg);  // stack is 4 bytes only. changes to f2 members will not
                                 // be seen by caller

void f3(const small_obj *arg); // stack is 4 bytes only. attempts within f3 to modify members
                               // should produce compiler warnings

void f4(small_obj& arg);   // similar to f2(), but uses C++ reference type

void f5(const small_obj& arg);   // similar to f3, but uses C++ reference type

void f6(large_obj arg);   // questionable.  This copys 9 MB onto the stack, which might
                          // be more than the OS can handle, and might incur performance
                          // penalties you can avoid by passing as a pointer or reference

The problem with global values, especially global values that are not local to a single file (e.g. declared as static), is it becomes increasingly more difficult to reason about where the variable gets modified. Given a function say print_item(void) you might not expect your global Item to get modified, but print_item() calls foo(void), which calls bar(void) which calls frobnicate(void), which modifies Item. If you are trying to trace down a bug, trying to see where Item gets modified can be difficult. On the other hand, calling print_item(const Item&), you can be (more or less) sure that Item doesn't get modified during the lifetime of print_item() (more or less because print_item() could be nasty and cast away constness, but that's an evil for another tale). Alternatively, you might have print_item(Item foo), which gets a local copy of Item, so the caller knows that whatever changes print_item might make to its copy, the callers Item remains unchanged.

Keep Calm and Carry On

Re: Pass a struct as a function parameter or just use it as a global variable?

Vaclav_18-Apr-20 7:30