Re: about change array length - C / C++ / MFC Discussion Boards

Re: Prevent Windows From Entering Hibernate Mode

Rishav Prabhakar14-Dec-11 20:39

14-Dec-11 20:39

That's the client side requirement so this wont be a hostile act..

and this code wont allow window to any state.. system will be continuously ON in windows 7

Re: Prevent Windows From Entering Hibernate Mode

C^hris L^osinger15-Dec-11 5:59

C^hris L^osinger

15-Dec-11 5:59

can't you just disable hibernation from the OS's power settings ?

seems cleaner than trying to do it from an application.

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Re: Prevent Windows From Entering Hibernate Mode

jeff616-Dec-11 23:24

jeff6

16-Dec-11 23:24

Juts disable it by schemes
code had been posted many times on pro win32 group

news://nntp.aioe.org/comp.os.ms-windows.programmer.win32
or http://tinyurl.com/cmhb5g by Google

about change array length

desatir731613-Dec-11 21:02

desatir7316

13-Dec-11 21:02

how we can change array length in c and c++?
for example: dose the programmer have to dispose the allocated memory and reallocate a new space in memory or the own language do this?

thanks if gimme a good document about it.
I need the answer in design programming language scope.
thanks so much.

Re: about change array length

Richard MacCutchan13-Dec-11 22:15

Richard MacCutchan

13-Dec-11 22:15

desatir7316 wrote:
dose the programmer have to dispose the allocated memory and reallocate a new space

Yes.

See here[^] for details about the C++ language.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

Re: about change array length

CPallini14-Dec-11 1:57

CPallini

14-Dec-11 1:57

In C programming language:
If you allocate the array on the stack then you cannot change its size.
On the other hand, if you allocate an array on the heap (using, for instance malloc) then you may change the size calling realloc.

All the above rules hold for C++. However you usually use the new operator for allocating arrays on the heap and new lacks of a reallocating mechanism. Anyway C++ provides, via the STL library, containers[^] that take care about memory reallocation.

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: about change array length

Randor 14-Dec-11 10:31

Randor

14-Dec-11 10:31

CPallini wrote:
In C programming language:

If you allocate the array on the stack then you cannot change its size.

Heh, don't forget about that Microsoft non-standard _malloca[^] beast that was added to the CRT a few years ago.

-Dave the Nitpicker. Big Grin | :-D

Re: about change array length

CPallini14-Dec-11 11:44

CPallini

14-Dec-11 11:44

Hey man, if it is Microsoft then it is 'the standard'!
Big Grin | :-D

Re: about change array length

David Crow14-Dec-11 3:27

David Crow

14-Dec-11 3:27

The first thing I thought of was realloc(), but then I got a twinge in my side and remembered this.

If you are using C++, consider a container. Your friends will thank you for it.

"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

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Re: about change array length

CPallini14-Dec-11 11:43

CPallini

14-Dec-11 11:43

Very good link. Smile | :)

Re: about change array length

szpillka15-Dec-11 5:32

szpillka

15-Dec-11 5:32

Unfortunaltely C/C++ does not allow programmer to use something similar to Delphi's setlength procedure, so that array once set length cannot be resized. When u want to resize, u must declare new array with bigger size, copy elements from old to new, delete old array. So therefore STL has some classes-containers, most often used by me is a list (from #include (list))

Read about list, vector, map, check Google

A quastion in programming language desing' scope

desatir731613-Dec-11 20:43

desatir7316

13-Dec-11 20:43

hello
what is difference between these assigning values for "a" and "b" ?

C++

class c1{
int a;
int b;
c1():b(0){
a=3;
}
}

thanks a lot

Re: A quastion in programming language desing' scope

Orjan Westin14-Dec-11 0:05

Orjan Westin

14-Dec-11 0:05

b is assigned first, since class initialising is executed before the constructor body. This is also the only place where you can assign a value to a non-static const or reference member variable.

Re: A quastion in programming language desing' scope

David Crow14-Dec-11 3:32

David Crow

14-Dec-11 3:32

See here.

what is the result(union & structure)?

desatir731613-Dec-11 20:32

desatir7316

13-Dec-11 20:32

hi there
can someone say what is the answer of this piece of code
by the way it is so important that why this answer made by the code in Programming language's scope
tnx

C++

union U{
struct S{
shortint x;
shortint y;
}
float f;
long l;
}u1;
u1.S.x=3;
u1.s.y=4;
cout<<f;
cout<<l;

Re: what is the result(union & structure)?

Richard MacCutchan13-Dec-11 22:13

Richard MacCutchan

13-Dec-11 22:13

The answers will most likely be garbage as the code refers to three different types in the same piece of memory. The float and long values will not have been initialised properly.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

Re: what is the result(union & structure)?

CPallini14-Dec-11 2:33

CPallini

14-Dec-11 2:33

Your code is utterly broken. A more compiler-friendly one could be:

C++

#include <iostream>
using namespace std;

union U
{
  struct S
  {
    short int x;
    short int y;
  }s;
  float f;
  long l;
} u1;

int main()
{
  u1.s.x=3;
  u1.s.y=4;

  cout << u1.f << endl;
  cout << u1.l << endl; 

}

Now let's have a look at the u1 memory layout (at least on my 32 bit machine):

ADDR      00 01 02 03
VALUE     03 00 04 00

where addresses are relative to &u1.
Since the (my) machine is little endian, we have the following bit configuration

BYTES   0    0    0    4    0    0    0    3
BITS  0000 0000 0000 0100 0000 0000 0000 0011

That is, for the float member,

SIGN     0
EXP      0
MANTISSA 00001000000000000000011

That is a denormalized float (see here[^]) with value

(2^-5 + 2^-22 + 2^-23) * 2^-126 = 3.6735039242275079514265571025945 * 10^-40

that looks similar to the program output: 3.67346E-040

Re: what is the result(union & structure)?

Richard MacCutchan14-Dec-11 2:40

Richard MacCutchan

14-Dec-11 2:40

Excellent answer.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

Re: what is the result(union & structure)?

CPallini14-Dec-11 2:42

CPallini

14-Dec-11 2:42

Thank you, Richard. Smile | :)

Re: what is the result(union & structure)?

Stefan_Lang14-Dec-11 5:34

Stefan_Lang

14-Dec-11 5:34

While C.Pallini's response may be correct, there is no guarantee, as the internal format of float is not defined by the standard and therefore compiler-specific! There may even be compiler options to use a specific representation, so the result may change depending on those options.

Also the standard does not specify that long is a 32 bit type, only that it must be at least 32 bit. While I know of no compiler that does this*, any compiler is free to use more than 32 bits, especially when the OS is not 32 bit! If for instance long were a 64 bit type, the value of l would be 3*2^48+4*2^32, which is a lot bigger than 3*2^16+4 in case of a 32 bit long type.

*compilers that support bigger than 32 bit integer types usually provide them by different names, such as 'long long' or '__int64', rather than just 'long'

Re: what is the result(union & structure)?

CPallini15-Dec-11 10:10

CPallini

15-Dec-11 10:10

As you correctly note, the particular memory layout I considered is not assured (this is why I specified 'on my 32 bit', 'little endian' machine and so on). My aim was to give him a method for investigating such matter.
Smile | :)

How to Convert vector::reference to vector::iterator ?

002comp13-Dec-11 20:21

002comp

13-Dec-11 20:21

Hello Friends

I am using vector and I used vector::iterator to iterate over the elements.
And after that I am using vector::reference = vector.back() to access last element.

Now,i want to assign all these refernce value to iterator one.

Any Ideas ?

Thanks & Regards
Yogesh

Re: How to Convert vector::reference to vector::iterator ?

C^hris L^osinger14-Dec-11 2:22

C^hris L^osinger

14-Dec-11 2:22

C++

for (int i=1;i<vec.size();i++) vec[i] = vec[0];

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Re: How to Convert vector::reference to vector::iterator ?

Stefan_Lang14-Dec-11 5:40

Stefan_Lang

14-Dec-11 5:40

You can't. The type of vector<T>::reference is T&, and has no reference to the original vector object, only to one element of type T.

The only way to assign an iterator is either through one of the methods of vector, or by assigning another iterator.

If you want an iterator to the last element, you can do this:

C++

std::vector<int> myvector(5); // 5 elements
std::vector::iterator last = myvector.end(); // points past the last element
--last; // now points at the last element

P.S.: after rereading your question I think I may have misinterpreted your question. If this isn't what you wanted and need more help, please clarify.

Re: How to Convert vector::reference to vector::iterator ?

002comp14-Dec-11 17:30

002comp

14-Dec-11 17:30

Thanks For your Answers.
I also proceed with the Stefan Method.

Thanks A Lot.
Regards
Yogesh

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