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Old Question Revisited, (comparing file data)

Posted on 2000-04-19
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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

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Question by:kainhart
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5 Comments
 
LVL 1

Expert Comment

by:ntdragon
ID: 2733637
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
ID: 2733738
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 400 total points
ID: 2733779
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
ID: 2734726
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
ID: 2748883
Thanks a lot I made this change and it made me function work like a charm.
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