C / C++ / MFC

002comp25-Apr-12 3:05

002comp

25-Apr-12 3:05

I am using Vs2008 professional.

Thanks For Your Reply.
Trying To Understand.

Thanks
Yogesh

JohnCz25-Apr-12 3:47

JohnCz

25-Apr-12 3:47

OK, that is good so far. If you have SP1 installed, why not to follow my previous advice (from my earlier response):

If you are using VS 2008 with feature pack or with SP1 use CMFCButton class. To set button face color, call SetFaceColor member. You have to set m_bTransparent to FALSE anf disable teaming by calling EnableWindowsTheming member and passing FALSE as parameter.

This is much easier than reinventing a wheel.

JohnCz

002comp25-Apr-12 7:51

002comp

25-Apr-12 7:51

Hello JohnCz
I tried to use CMFCButton but there is no class in VS2008 prof.
Do i need to link up something?

Thanks Again.
Regards
Yogesh

David Crow25-Apr-12 8:09

David Crow

25-Apr-12 8:09

yogeshs wrote:
I tried to use CMFCButton...

How? When you added a button to the dialog template and went to assign a variable to it, the Add Member Variable Wizard defaulted to CButton. All you need to do is change that to CMFCButton. The appropriate header file (i.e., afxbutton.h) would have been added automatically, if it was not already included.

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JohnCz26-Apr-12 2:28

JohnCz

26-Apr-12 2:28

Hi yogeshs,
You have to learn how to be patient and read all answers and documentation without skipping some parts.
I have already mentioned twice:

If you are using VS 2008 with feature pack or with SP1 use CMFCButton class.
You need Visual Studio SP1 installed.

Web installer[^]

ISO image[^]

Than you can subclass button using CMFCCustButton.
Subclassing is easy if you use wizard:
Right click on the button in the resource editor and choose Add Variable.
The only option you have is CButton, so select it.
After wizard closes, open dialog’s header file and change CButton to CMFCMenuButton.

JohnCz

David Crow25-Apr-12 2:39

David Crow

25-Apr-12 2:39

yogeshs wrote:
CColorbutton* pBtn = new CColorButton();
pBtn->Attach(GetDlgItemId( IDC_BUTTON_ID + ndx )->GetSafeHwnd());

It's highly unlikely that you would need to do this. Why not just replace CButton with CColorbutton in your dialog's .h file?

Reference return vs Pointer return

002comp25-Apr-12 7:55

002comp

25-Apr-12 7:55

Hello david
I didnt get your point.

Regards
Yogesh

Aragtey24-Apr-12 0:05

Aragtey

24-Apr-12 0:05

Hi all,

i was just wondering if what are the advantages/disadvantages of a reference return vs a pointer return?

Suppose if we have a large vector of objects in terms of performance there is any difference between returning a pointer to a object or the object reference.

Thanks

CPallini24-Apr-12 0:56

CPallini

24-Apr-12 0:56

What do you mean with 'reference' return?
Usually you obtain 'out' parameters as arguments passed by reference.
Moreover, there is no performance penalty in passing values by reference.

Veni, vidi, vici.

enhzflep24-Apr-12 1:10

enhzflep

24-Apr-12 1:10

In terms of performance, they're identical.

In practise, references mean you can use the . operator instead of the -> operator to access member functions/variables.

While there are a considerable number of differences between the two (look into operator overloading - it relies on references), I've just concentrated on the difference as it relates to your question.

[EDIT:] What CPallini said, above.

Aescleal24-Apr-12 1:55

Aescleal

24-Apr-12 1:55

There are loads of different rules you can apply here...

- Are you writing a member operator? Return *this by reference

- Are you writing a non-member operator? Return by value and either do your damnedest to trigger NRVO/RVO or write a move constructor in C++11

- Are you transferring ownership of something? Return a std::unique_ptr

- Do you want to read something that legitimately might or might not exist? Use a const pointer using 0 as an error value

- Do you want to read something that should exist and if it doesn't then the whole program's sunk? Return a const reference and throw if something goes wrong

- Are you returning a writable address or a reference to one or more of an object's data members? You are insane, please report to the funny farm

- Do you want to return a reference to an object to an automatic variable? See previous answer for details.

One thing to remember though is that sometimes you'll want to do something that's a bit unusual and you'll have to do something unusual to implement it.

Cheers,

Ash

Aragtey24-Apr-12 5:37

Aragtey

24-Apr-12 5:37

Thanks for all the answers.

Giving an example:

C++

vector<int> my_vec;

int* get_int(int positon) {
   int* value = my_vec.at[position]
   return value;
}

int& get_int(int positon) {

   return my_vec.at[position];
}

So both cases will avoid a copy of the object and will be fast them passing by value but besides that what are the differences.

References cant be null so probably returning by reference will have to assure that case, but im more concern in vantages of one side to the other (if there are any).

Thanks

Aescleal24-Apr-12 6:31

Aescleal

24-Apr-12 6:31

In both those case I'd return a value, not a reference or pointer. Unless you want to directly modify what's in the vector in which case you'd just use operator[].

Basically return by value first, if that's not what you want use pointers when failure isn't critical, references otherwise.

Cheers,

Ash

Aragtey24-Apr-12 6:36

Aragtey

24-Apr-12 6:36

The example is for a vector<int> and in this case its better returning by value, but in cases where we have a vector<my_object> and the object class is big its better returning a reference or a pointer. Just would like to know in those cases which one is better?

Thanks

Best approach to compare files

Aescleal25-Apr-12 5:19

Aescleal

25-Apr-12 5:19

Neither - always return by value from a vector. Don't mess about with storing pointers or references. And if you have to store something by reference use a shared_ptr.

If you write the class being stored in the vector correctly (fast default construction, move constructor, transactional exception safe assignment operator, using named return values) copying objects out of collections is very fast.

Cheers,

Ash

MKC00223-Apr-12 23:37

MKC002

23-Apr-12 23:37

If there are some directories and each directory contains some files then i want to make a program which will compare each file of any directory with each file of all directories.
Can someone suggest me a best approach which works faster and dont miss any comparision.

sangamdumne23-Apr-12 23:49

sangamdumne

23-Apr-12 23:49

Hi friend,
use findfirstfile() and findnextfile()
msdn api's.....hope this will help you

MKC00224-Apr-12 0:22

MKC002

24-Apr-12 0:22

Hi,
Thanks for your reply. FindFirst/Next file will give me file name.
Here i asked about the approach i.e. container and logic to implement comparision which should be faster and reliable.

enhzflep24-Apr-12 1:35

enhzflep

24-Apr-12 1:35

It really depends on what kind a value you wish to return from the function.

For instance I can envisage two basic approaches - true/false for same/not same, or a -/0/+ value as strcmp does.

Here's an approach that just returns true/false.
I've timed it - it takes 6 seconds to compare a 347MB video file with itself - Win7 Home Premium x64, Intel i3 @ 2.13Ghz, 4GB ram - gcc 4.4.1

C++

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void loadFile(char *szFilename, size_t &sizeOut, char* &bufferOut)
{
    FILE *fp;

    fp = fopen(szFilename, "rb");
    fseek(fp, 0, SEEK_END);
    sizeOut = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    bufferOut = (char*) malloc(sizeOut);
    fread(bufferOut, 1, sizeOut, fp);
    fclose(fp);
}

bool isSame(char *szFilename1, char *szFilename2)
{
    size_t len1, len2;
    long curPos;
    char *buffer1, *buffer2;
    bool result = true;

    loadFile(szFilename1, len1, buffer1);
    loadFile(szFilename2, len2, buffer2);

    if (len1 == len2)
    {
        for (curPos=0; curPos<len1; curPos++)
        {
            if (buffer1[curPos] != buffer2[curPos])
                result = false;
        }
    }

    else
        result = false;

    free(buffer1);
    free(buffer2);
    return result;
}


int main()
{
    if (isSame("testVideo.avi", "testVideo.avi"))
        printf("Same\n");
    else
        printf("Not Same\n");
}

image processing toolkits | batch image processing

C^hris L^osinger24-Apr-12 1:46

C^hris L^osinger

24-Apr-12 1:46

for SuperDuper[^] i did this:

0. build the list of files to compare.
1. read the first 1000 bytes of each file to compare.
2. from those 1000 bytes, generate an SHA1 hash.
3. store the hashes, file size, and file names in a list
4. sort the list by hash values. duplicates will clump together.
5. for hash matches, do a full file compare.

Randor 24-Apr-12 20:35

Randor

24-Apr-12 20:35

Chris Losinger wrote:
2. from those 1000 bytes, generate an SHA1 hash.

3. store the hashes, file size, and file names in a list

Why would you want to waste all those cpu cycles by calculating a SHA1 hash? If you know that the maximum number of bytes you're going to read is 1000 then you could have used an inexpensive hashing algorithm... there are dozens of inexpensive hash algorithms that will have a collision probability of zero within 1000 bytes. Your application would probably have a huge performance boost. Not to mention... the SHA1 hash will produce 20 bytes of data to store... you could reduce your database size by 50% just by moving to a more efficient algorithm.

Were you initially planning on hashing the entire file or something?

Best Wishes,
-David Delaune