C / C++ / MFC Discussion Boards

Re: 10 & 10/3*3 are not equal ! ! ! WHY?

EverettJF13-Jul-10 14:47

13-Jul-10 14:47

i remember,when i was a student,
my c language teacher told me , if i compare two "float" or "double", i should check it between a very little number.
such as ,

const float c_tmp = 0.000001;
bool b;
float f1 = 10.0;
float f2 = f1 / 3;
b = (f1 >= (f2 * 3.0) - c_tmp) && (f1 <= (f2 * 3.0) + c_tmp);

Re: 10 & 10/3*3 are not equal ! ! ! WHY?

Rick York13-Jul-10 16:32

Rick York

13-Jul-10 16:32

or you could write

double difference = f1 - ( f2 * 3.0 );
bool b = fabs( difference ) < epsilon;

I think that is a little more self-explanatory plus it is faster since the calculations and comparisons are only performed once.

Re: 10 & 10/3*3 are not equal ! ! ! WHY?

Aescleal13-Jul-10 21:47

Aescleal

13-Jul-10 21:47

10 divided by 3 is 3.333 recurring in decimal and in binary it's something like: 11.01010101 (can't be bothered working it out any further). Say you have a computer which stores floats as 6 bits for the non-exponent chunk of the number. It'd truncate the value of 10/3 to 11.0101. When you multiply it by three you get: 1001.1111 which is truncated to 1001.11 which is 9.75 in decimal. While real double precision numbers use oodles more bits to represent the non-exponential part you get the same problem.

Note that you've got a similar problem with order of evaluation: (A * B ) / C for a computer using a finite number of bits is not necessarily equal to ( A / C ) * B. Fortunately most real world uses of computers don't have these problems - it's really only a concern to people doing simulation or some science. The rest of us can use integers most of the time and get away with it.

Cheers,

Ash

Re: 10 & 10/3*3 are not equal ! ! ! WHY?

josda100014-Jul-10 6:26

josda1000

14-Jul-10 6:26

In the code, you do this: float f2 = f1 / 3;
I believe you're looking for this: fload f2 = f1 / 3.0;
I'm not sure it's going to set b = true, however, it's more correct nontheless.

Josh Davis

This is what plays in my head when I finish projects.

DLL injection at start time.

Code-o-mat13-Jul-10 6:13

Code-o-mat

13-Jul-10 6:13

Hello people!

I'm experimenting with DLL injection and API hooking, there's no real goal to it, just playing around. So, injecting a DLL into a running process and hooking methods works fine, i have done that a few times already in the past so i have some experience.
Now, what i tried this time is to create a process with CreateProcess[^], specifying the flag CREATE_SUSPENDED to create the process' main thread suspended, then, i used the CreateRemoteThread method to inject a DLL, do some API hooking, and then called ResumeThread on the process' main thread. When i do this i hear a *clonk* soundeffect and the runned process does not start/exists prematurely. So i wonder, what could cause this? If i run the process "normally" and inject the DLL (with the same remote thread method) it works as expected.
Can anyone shed some light on this? Thanks for the answers.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> "It doesn't work, fix it" does not qualify as a bug report. <
> Amazing what new features none of the programmers working on the project ever heard of you can learn about when reading what the marketing guys wrote about it. <

Word automation using MFC - how to hide Word toolbar and menu bar

Member 422150713-Jul-10 4:46

Member 4221507

13-Jul-10 4:46

I use ActiveX container to host a Word document in my app. I want to hide Word toolbar and
menu bar.

I tried to use the following code

// app is an instance of _Application
CCommandBars cbs = app.GetCommandBars();
for (int i=1; i<=cbs.get_Count(); i++)
{
CCommandBar bar = cbs.get_Item(COleVariant((short)i));
bar.put_Enabled(false);
//bar.put_Visible(false);
}

I tried put_Enabled, it won't hide toolbar/menu bar.

I also tried put_Visible but it caused the Word document being closed.

I am wondering if some one can point me direction here.

Using Open SSL

Rajmohan SK13-Jul-10 3:54

Rajmohan SK

13-Jul-10 3:54

I want to build a SSL server application in VC++, unmanaged code, using OpenSSL.
I got many sample application of SSL Client. but the server sample application is not so frequent, the application which I got was not working . The problem I am facing is that I am not sure about the method of developing a server application and the usage of digital certificate. Can anybody help me how to do it or send me some useful links.

Any help will be appreciated

Thanks in advance

Regards

Rajmohan

Re: Using Open SSL

Aescleal13-Jul-10 4:11

Aescleal

13-Jul-10 4:11

Beg, borrow or steal a copy of "Network Security with OpenSSL" by Viega, Messier and Chandra. It doesn't describe the SSL protocol that well but it has a recipe for a client server app including where certificate checking fits in.

Cheers,

Ash

Re: Using Open SSL

Rajmohan SK13-Jul-10 17:57

Rajmohan SK

13-Jul-10 17:57

Thank you so much for the reply.

Regards

Rajmohan

const string reference variables

apphia_j_7913-Jul-10 2:43

apphia_j_79

13-Jul-10 2:43

A const string reference is being passed just as a string to another proc.The code crashes after the call a_proc(). Please give your inputs

Imp::Reset(const string& res_str, const bool& b)
{

a_proc(res_str);
a_get();

}

Imp::a_proc(string res_str)
{
//res_str is just validated
}

Re: const string reference variables

Cedric Moonen13-Jul-10 2:47

Cedric Moonen

13-Jul-10 2:47

Nothing wrong with passing the string a const reference, it's not the cause of the crash. Use your debugger to see where the crash occurs precisely and for what reason.

Cédric Moonen
Software developer

Charting control [v3.0]
OpenGL game tutorial in C++

Re: const string reference variables

apphia_j_7913-Jul-10 3:24

apphia_j_79

13-Jul-10 3:24

The Issue now is passing the variable that was retreived as a const string& is passed to another proc as just a string(passing by value). Any comments on this.
sorry, I don't have a debugger.

Re: const string reference variables

Cedric Moonen13-Jul-10 3:32

Cedric Moonen

13-Jul-10 3:32

As I said, there's nothing wrong with passing a string by const reference and it won't make any different. You are focusing on the wrong problem and should try to find the real cause of the problem.

apphia_j_79 wrote:
sorry, I don't have a debugger.

With which IDE are you coding Confused | :confused:

? Developping without a debugger is like cooking without knives Dead | X|

Cédric Moonen
Software developer

Charting control [v3.0]
OpenGL game tutorial in C++

Re: const string reference variables

CPallini13-Jul-10 2:58

CPallini

13-Jul-10 2:58

Probably you should post the actual code to get better help.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: const string reference variables

Aescleal13-Jul-10 3:52

Aescleal

13-Jul-10 3:52

And while you're thinking of posting your code consider why you're passing the string by value to a_proc and using a const reference to bool in Reset.

The first one I can see a point for if you were going to copy the string anyway to mangle it but the const bool &b thing doesn't make a lot of sense.

Oh, hang on, you're not casting it to something else in the function to modify it are you?

Ash

Re: const string reference variables

Niklas L13-Jul-10 4:42

Niklas L

13-Jul-10 4:42

You should check the string before sending it to Reset, or the object owning the string. Taking its reference might be ok even if the instance no longer exists, but once you dereference it, you might get an access violation.

Typically, problems like this occurs if your string is a member variable in an instance you have deleted (or is null).

class A
{
    string s;
public:
    void method() { Reset(s); }
};
A *a = nullptr;
a->method();

The above code will work when Reset() takes a reference to the string, but not if it accesses its value, which a call-by-value does.

home

C2782

T.RATHA KRISHNAN13-Jul-10 1:47

T.RATHA KRISHNAN

13-Jul-10 1:47

Hi!
I got the following while compiling my program.

d:\test\test\nrp2dpictureflow.cpp(90) : error C2782: 'const T &irr::core::min_(const T &,const T &,const T &)' : template parameter 'T' is ambiguous
1> e:\irrlicht-1.7.1\include\irrmath.h(123) : see declaration of 'irr::core::min_'
1> could be 'irr::u32'
1> or 'int'
1>d:\test\test\nrp2dpictureflow.cpp(90) : error C2780: 'const T &irr::core::min_(const T &,const T &)' : expects 2 arguments - 3 provided
1> e:\irrlicht-1.7.1\include\irrmath.h(116) : see declaration of 'irr::core::min_'

Th function min_ is defined as follows:

//! returns minimum of two values. Own implementation to get rid of the STL (VS6 problems)
	template<class T>
	inline const T& min_(const T& a, const T& b)
	{
		return a < b ? a : b;
	}

	//! returns minimum of three values. Own implementation to get rid of the STL (VS6 problems)
	template<class T>
	inline const T& min_(const T& a, const T& b, const T& c)
	{
		return a < b ? min_(a, c) : min_(b, c);
	}

Why the compiler expects the third value? What value do I have to pass as third argument to min_?

Re: C2782

Cedric Moonen13-Jul-10 2:09

Cedric Moonen

13-Jul-10 2:09

And what is your code actually ? Unsure | :~

Cédric Moonen
Software developer

Charting control [v3.0]
OpenGL game tutorial in C++

Re: C2782

Emilio Garavaglia13-Jul-10 7:20

Emilio Garavaglia

13-Jul-10 7:20

Check the way you're calling the function. The parameter you pass must have all the same type (or decade implicitly all into a same common type). If -for example- you pass an int and a float the compiler cannot decide which has to be converted into the other.

2 bugs found.
> recompile ...
65534 bugs found.
D'Oh! | :doh:

import a registry file in the registry editor

mazizi13-Jul-10 1:07

mazizi

13-Jul-10 1:07

is there any API which i can import a registry file in the registry editor? moreover in my registry file is a key which need full control permission for everyone in HKEY_LOCAL_MACHINE, how can i get this through source?!
thanks

Re: import a registry file in the registry editor

Electron Shepherd13-Jul-10 3:05

Electron Shepherd

13-Jul-10 3:05

mazizi wrote:
is there any API which i can import a registry file in the registry editor?

http://msdn.microsoft.com/en-us/library/ms724889.aspx[^]

mazizi wrote:
need full control permission for everyone in HKEY_LOCAL_MACHINE, how can i get this through source?!

http://msdn.microsoft.com/en-us/library/aa379314.aspx[^]

Server and Network Monitoring

Re: import a registry file in the registry editor

mazizi13-Jul-10 19:14

mazizi

13-Jul-10 19:14

thanks a lot for your attention, but i want to use just one function to import file to registery editor, something like "import" option in "file" menu of registry editor since there is lots of keys in HKEY_CLASSES_ROOT, HKEY_CURRENT_USER and HKE_LOCAL_MACHINE in this file, and i don't want to import them separately.
moreover be conscious please, i have to use MFC i'm NOT allowed to use .net framework.
thanks for your help

Spin Control

AbhiHcl13-Jul-10 0:52

AbhiHcl

13-Jul-10 0:52

How to show the time value in edit control which is attached with spin control. I also need increase or decrease the time value with the help of Spin control..
Please help me..

Thanks..

Re: Spin Control

Richard MacCutchan13-Jul-10 1:33

Richard MacCutchan

13-Jul-10 1:33

Use one of the time[^] functions to obtain a string with the current time which you can display in the edit box. Use the spinner controls to adjust the values (based on selected characters) up or down and adjust your time value as necessary.

It's time for a new signature.

Re: Spin Control

AbhiHcl13-Jul-10 21:40

AbhiHcl

13-Jul-10 21:40

can u please provide me some sample code as I m very new in MFC..

Thanks..

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