Opening a Binary File

Dream86 · #1 22-Sep-2004, 14:40

Hi,
My program is suppose to scan the directory, and count the number of files in it. The number of files in the direcotry should be appended to the name of the output file which can be selected by the user. After that, it is suppose to read the first 512 bytes of the first file in the direcoty according to a certain format. (the files are image files output of a microscope and they have 512 b header that contains the information about that specific image.) after the program scans and counts the number of directories, the pointer is put at the beginning of the directory, then it skips "." and " .. " and start by reading the byte 16 of the first file. I used seekg to put the pointer at byte 16.
The tellg(), however gives back a value of -1. When i checked to see if the file opens properly or not using fail(), i got the error message, showing that the file has not been opened corectly. How can i know what is going wrong here?

here is the the corresponding code for this part:

CPP / C++ / C Code:

 while ( (ent = readdir(dir)) != NULL)
  {
 
    if ( (strcmp((char*)ent->d_name, ".") != 0) && (strcmp((char*)ent->d_name, "..") != 0) )
    {
  
        ifstream inFile(ent->d_name, ios::in |ios::binary);

        if (inFile.fail())
        {

         //ERR message

         }

         else

         {...}

...
}

Thanks

davekw7x · #2 23-Sep-2004, 08:35

Quote:

Originally Posted by Dream86

Hi,
My program is suppose to scan the directory
...

When i checked to see if the file opens properly or not using fail(), i got the error message, showing that the file has not been opened corectly. How can i know what is going wrong here?

Thanks

There is no way that I can tell you why the file failed to open. You can get clues from your own program.

Are you sure that you are trying to open the right file? Put in a line to show the file name. Something like the following:

CPP / C++ / C Code:

  cout << "Trying to open <" << ent->d_name << ">" << endl;
   ifstream inFile(ent->d_name, ios::in |ios::binary);

If the file name is correct, does the file exist in the directory where your executable is?

Regards,

Dave

LuciWiz · #3 23-Sep-2004, 09:42

Hm, I remember this problem from another thread....
I only suggested the fail thing, but then I failed to answer your next question. Unfortunatelly, what I wanted to suggest was something like Dave already did

Print the exact path to your file as you have it in your program (obtained through argv). Maybe it's not what you would expect (I'm thinking something like "c:\bla\bla", and then your filename, instead of "c:\bla\bla\" and then your filename - I'm only suggesting this because it happened to me ;-) )
So, please get back to us when you did it.

Best regards,
Luci

Dream86 · #4 23-Sep-2004, 21:14

I have already tried to print out the name of the file that is supposed to be opened. It seems to be fine. I mean it prints the correct file name.
I do not compeltely understand what you mean by defining the path of the file. The program is suppose to go through the files in a (sub)directory one by one. It asks for the name of the directory, and the direcoty that contains the files is in the same directory as the program.
do i need to specify the path of the directory in the ifstream ? something like :

CPP / C++ / C Code:

ifstream inFile(c:\ent->d_name, ios::in | ios::binary);

Thank you

Dream86 · #5 23-Sep-2004, 22:21

well, i actually tried

CPP / C++ / C Code:

ifstream inFile(c:\ent->d_name, ios::in | ios::binary);

and it did not work.
Since it gives back the name of the file that is supposed to be read correctly, does not that mean the program has already located the file properly?

thanks

Dream86 · #6 23-Sep-2004, 22:24

Quote:

Originally Posted by LuciWiz

Print the exact path to your file as you have it in your program (obtained through argv). Maybe it's not what you would expect (I'm thinking something like "c:\bla\bla", and then your filename, instead of "c:\bla\bla\" and then your filename -Luci

I am sorry but i do not quite follow you here. would you please explain...

thank you

LuciWiz · #7 24-Sep-2004, 03:12

Quote:

Originally Posted by Dream86

I am sorry but i do not quite follow you here. would you please explain...

thank you

I'm sorry I didn't answer very promptly, but when you posted it was 5-6 A.M. in my country. I was sleeping like a baby

I hope you didn't literrally try this:

CPP / C++ / C Code:

ifstream inFile(c:\ent->d_name, ios::in | ios::binary);

but, rather like this:

CPP / C++ / C Code:

ifstream inFile("c:\\" + ent->d_name, ios::in | ios::binary);

Observe the double "\\"(that's Windows)
Of course, this kind of concatenation will not work under C (you'll get something about adding 2 pointers). It works with VC CStrings, though

You' can do something with std:string and Insert, I don't mean to bore you...
However, since it is in a (sub)directory of your application's directory, you still need something like:

CPP / C++ / C Code:

destFile = directoryName + "\\" +  ent->d_name;
ifstream inFile(destFile, ios::in | ios::binary);

Quote:

Originally Posted by Dream86

Since it gives back the name of the file that is supposed to be read correctly, does not that mean the program has already located the file properly?

Does it print "SubDirectoryName\FileName"?

BTW, I'm away for the weekend (Motivational Weekend

), so I hope you solve this....

Best of luck,
Luci

Dream86 · #8 28-Sep-2004, 16:33

My Problem was resolved

Thank you

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