Solved

Old Question Revisited, (comparing file data)

Posted on 2000-04-19
5
189 Views
Last Modified: 2010-04-02
I asked a question about how to compare to files if they have exacly the same content. For example in windows you copy a file and change it's name so it's basically the same file with a different name. The answer I got was to make a the function listed below. I used this function for a while until I got a nice hex editor and I found out that even if the files were somewhat different, that the function was still saying that they were duplicates. Here is a listing of my function with a small driver.


#include <fstream.h>
#include <string.h>

bool CompareFileData(const char *Fil1, const char *Fil2)
// Returns TRUE if the files have the same content
// Returns FALSE otherwise
{
      fstream inDataFile1(Fil1,ios::in || ios::binary);
      fstream inDataFile2(Fil2,ios::in || ios::binary);
      const int BufferSize = 1024;
      char Buffer1[BufferSize];
      char Buffer2[BufferSize];
      int RedLen1;                        // what are these are for?
      int RedLen2;

      while (true)    
      {
            inDataFile1.read(Buffer1,BufferSize);
            RedLen1 = inDataFile1.gcount();  // what does this function do?
            inDataFile2.read(Buffer2,BufferSize);
            RedLen2 = inDataFile2.gcount();
            if (RedLen1 != RedLen2)
                  return false;            
            if (RedLen1 == 0)
                  return true;
            if (memcmp(Buffer1,Buffer2,RedLen1))
                  return false;
      }
}

void main()
{
      char fileName1[120] = {"G:\\download\\testfolder\\copy1.jpg\0"};
      char fileName2[120] = {"G:\\download\\testfolder\\copy2.jpg\0"};

      if(CompareFileData(&fileName1[0], &fileName2[0]))
            cout << "\n\nThese files are the same.\n";
      else
            cout << "\n\nThese files are not the same.\n";
}

I'm really frustrated with all the different available functions for reading file buffers and such, and I don't know why I'm using char arrays when I'm trying to deal with binary data. If somebody can figure out why this function is not working and explain it to me I would greatly appreciate it. Thanks

0
Comment
Question by:kainhart
5 Comments
 
LVL 1

Expert Comment

by:ntdragon
Comment Utility
why don't you read all the file to the memory and then use strcmp
i mean you can read the two files to two
char* and then compaire them with strcmp

i'm not sure about your code i"ll go to my second comp and rewrite the func for you for now as i understand

the:
int RedLen1; // what are these are for?
int RedLen2;
//will keep the length of files

RedLen1 = inDataFile1.gcouent();  // what does this function do?
//gets the length of the file
0
 
LVL 1

Expert Comment

by:ntdragon
Comment Utility
first version :

#include <fstream.h>
#include <string.h>

bool CompareFileData(const char *Fil1, const char *Fil2)
// Returns TRUE if the files have the same content
// Returns FALSE otherwise
{
fstream inDataFile1(Fil1,ios::in || ios::binary);
fstream inDataFile2(Fil2,ios::in || ios::binary);
char *Buffer1;
char *Buffer2;
int RedLen1;
int RedLen2;

inDataFile1.seekg(2);
RedLen1=inDataFile1.tellg ();
inDataFile1.seekg (0);

inDataFile2.seekg(2);
RedLen2=inDataFile2.tellg ();
inDataFile2.seekg (0);

if (RedLen1 != RedLen2)
return false;
if (RedLen1 == 0)
return true;
Buffer1=new char[RedLen1+1];
inDataFile1.get(Buffer1,RedLen1);

Buffer2=new char[RedLen1+1];
inDataFile2.get(Buffer2,RedLen2);

if (strcmp(Buffer1,Buffer2))
return false;
return true;
}

void main()
{
char fileName1[120] = {"G:\\download\\testfolder\\copy1.jpg\0"};
char fileName2[120] = {"G:\\download\\testfolder\\copy2.jpg\0"};

if(CompareFileData(fileName1, fileName2))
cout << "\n\nThese files are the same.\n";
else
cout << "\n\nThese files are not the same.\n";
}

//end

second version:

#include <fstream.h>
#include <string.h>

bool CompareFileData(const char *Fil1, const char *Fil2)
// Returns TRUE if the files have the same content
// Returns FALSE otherwise
{
fstream inDataFile1(Fil1,ios::in || ios::binary);
fstream inDataFile2(Fil2,ios::in || ios::binary);
char Buffer1;
char Buffer2;
int RedLen1;
int RedLen2;

inDataFile1.seekg(2);
RedLen1=inDataFile1.tellg ();
inDataFile1.seekg (0);

inDataFile2.seekg(2);
RedLen2=inDataFile2.tellg ();
inDataFile2.seekg (0);

if (RedLen1 != RedLen2)
return false;
if (RedLen1 == 0)
return true;

while (!inDataFile1.eof()){
inDataFile1>>Buffer1;
inDataFile2>>Buffer2;
if (Buffer1!=Buffer2)
return false;
}
return true;
}

void main()
{
char fileName1[120] = {"G:\\download\\testfolder\\copy1.jpg\0"};
char fileName2[120] = {"G:\\download\\testfolder\\copy2.jpg\0"};

if(CompareFileData(fileName1, fileName2))
cout << "\n\nThese files are the same.\n";
else
cout << "\n\nThese files are not the same.\n";
}

//end

check them there maybe bugs about the length of the file but i think it should work
0
 
LVL 2

Accepted Solution

by:
Serega earned 100 total points
Comment Utility
Kainhart, in order that your function to work, you should to change constructors:
your:

fstream inDataFile1(Fil1,ios::in || ios::binary);
fstream inDataFile2(Fil2,ios::in || ios::binary);

necessary:
ifstream inDataFile1(Fil1,ios::binary);
ifstream inDataFile2(Fil2,ios::binary);

0
 
LVL 14

Expert Comment

by:AlexVirochovsky
Comment Utility
to ntdragon: you can't use
strcmp for test binary data(becouse
must test 0x00 and after this too.
see, that original text(of nietod?) use
memcmp.
0
 

Author Comment

by:kainhart
Comment Utility
Thanks a lot I made this change and it made me function work like a charm.
0

Featured Post

IT, Stop Being Called Into Every Meeting

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

Join & Write a Comment

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
This article shows you how to optimize memory allocations in C++ using placement new. Applicable especially to usecases dealing with creation of large number of objects. A brief on problem: Lets take example problem for simplicity: - I have a G…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

728 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

9 Experts available now in Live!

Get 1:1 Help Now