Reading Binary files

earth_angel · 07-11-2005, 10:01 AM

Hey,

I've looked over the binary I/O post and read over some tutorials on line, but I still can't make the program read in a binary number properly.

I've tried:

Code:

 char num[5];
   int DataFormat;

   inp>>DataFormat;

   // and 

   inp.read(num, sizeof(long)); 
   num[5] = '\0';
   DataFormat = atoi(num);

It doesn't interprit DataFormat properly in either case. The input file is binary. to place the poiter at the correct position I use:

Code:

ifstream inp;
   inp.open("test.baf", ios_base::binary);

    inp.seekg(549,ios::beg);

is there another way to read in 4 bytes into a longint variable fro ma binary file?

manannan · 07-11-2005, 10:10 AM

Try

Code:

long x;

inp.read(&x, sizeof(long);

You might need to cast &x to char*.

earth_angel · 07-11-2005, 11:06 AM

Nope, doesn't work either.
Thanks though.

kuphryn · 07-11-2005, 11:28 AM

Check out this line:

num[5] = '\0';

Post an example of the bytes that is read from the file and the incorrect value assigned to DataFormat.

Kuphryn

earth_angel · 07-11-2005, 11:55 AM

Code:

	DataFormat	-858993460
	&DataFormat	0x0012f5bc

thant's using : inp.read((char*)&DataFormat, sizeof(long));

If I use

Code:

inp.read(num, sizeof(long)); 
   num[5] = '\0';
   DataFormat = atoi(num);

I get

Code:

	DataFormat	-858993460
-	num	0x0012f5c0 "ÌÌÌÌÌ"
	[0]	-52 'Ì'
	[1]	-52 'Ì'
	[2]	-52 'Ì'
	[3]	-52 'Ì'
	[4]	-52 'Ì'
	num[5]	0 ''

swoopy · 07-11-2005, 12:17 PM

Code:

inp.read((char*)&DataFormat, sizeof(long));

is correct (assuming a 4 byte int). Or better is:

Code:

inp.read((char*)&DataFormat, sizeof(DataFormat));

What's actually in your file at locations 549-552?

C+noob · 07-11-2005, 12:27 PM

this is advance but i remember that you have to treat the file as binary while opening it

Code:

ofstream file ( "file.file", ios::binary );

earth_angel · 07-11-2005, 12:32 PM

>What's actually in your file at locations 549-552?

It should be 0,1 or 2 as a long int.

>you have to treat the file as binary while opening it
I do use ios::binary

C+noob · 07-11-2005, 12:43 PM

god im stupid lol didnt read all of it hahaha sry

swoopy · 07-11-2005, 04:39 PM

I would verify the data with this then (first seek to appropriate location):

Code:

char ch;

inp.read((char*)&ch, sizeof(ch));
cout << (int) ch << " ";
inp.read((char*)&ch, sizeof(ch));
cout << (int) ch << " ";
inp.read((char*)&ch, sizeof(ch));
cout << (int) ch << " ";
inp.read((char*)&ch, sizeof(ch));
cout << (int) ch << " ";
cout << endl;

It's possible the bytes are reversed (endian problem), but first see if the data looks right.

earth_angel · 07-12-2005, 06:48 AM

I've tried everything above. It doesn't come back properly. let me look into the file structure a bit more. Maybe I'm forgetting something there. Maybe later I'll be back with a new problem.
Thanks for all the help,

AS.

07-11-2005, 10:01 AM	#1
earth_angel Registered User Join Date: May 2005 Location: Toronto, Canada Posts: 257	Reading Binary files Hey, I've looked over the binary I/O post and read over some tutorials on line, but I still can't make the program read in a binary number properly. I've tried: Code: char num[5]; int DataFormat; inp>>DataFormat; // and inp.read(num, sizeof(long)); num[5] = '\0'; DataFormat = atoi(num); It doesn't interprit DataFormat properly in either case. The input file is binary. to place the poiter at the correct position I use: Code: ifstream inp; inp.open("test.baf", ios_base::binary); inp.seekg(549,ios::beg); is there another way to read in 4 bytes into a longint variable fro ma binary file?
earth_angel is offline

07-11-2005, 10:10 AM	#2
manannan Registered User Join Date: Jul 2005 Posts: 25	Try Code: long x; inp.read(&x, sizeof(long); You might need to cast &x to char*.
manannan is offline

07-11-2005, 11:06 AM	#3
earth_angel Registered User Join Date: May 2005 Location: Toronto, Canada Posts: 257	Nope, doesn't work either. Thanks though.
earth_angel is offline

07-11-2005, 11:28 AM	#4
kuphryn Registered User Join Date: Nov 2001 Posts: 1,348	Check out this line: num[5] = '\0'; Post an example of the bytes that is read from the file and the incorrect value assigned to DataFormat. Kuphryn
kuphryn is offline

07-11-2005, 12:17 PM	#6
swoopy Registered User Join Date: Oct 2001 Posts: 2,936	Code: inp.read((char)&DataFormat, sizeof(long)); is correct (assuming a 4 byte int). Or better is: Code: inp.read((char)&DataFormat, sizeof(DataFormat)); What's actually in your file at locations 549-552? __________________ http://www.freechess.org
swoopy is offline

07-11-2005, 12:32 PM	#8
earth_angel Registered User Join Date: May 2005 Location: Toronto, Canada Posts: 257	>What's actually in your file at locations 549-552? It should be 0,1 or 2 as a long int. >you have to treat the file as binary while opening it I do use ios::binary
earth_angel is offline

07-11-2005, 04:39 PM	#10
swoopy Registered User Join Date: Oct 2001 Posts: 2,936	I would verify the data with this then (first seek to appropriate location): Code: char ch; inp.read((char)&ch, sizeof(ch)); cout << (int) ch << " "; inp.read((char)&ch, sizeof(ch)); cout << (int) ch << " "; inp.read((char)&ch, sizeof(ch)); cout << (int) ch << " "; inp.read((char)&ch, sizeof(ch)); cout << (int) ch << " "; cout << endl; It's possible the bytes are reversed (endian problem), but first see if the data looks right. __________________ http://www.freechess.org
swoopy is offline

07-12-2005, 06:48 AM	#11
earth_angel Registered User Join Date: May 2005 Location: Toronto, Canada Posts: 257	I've tried everything above. It doesn't come back properly. let me look into the file structure a bit more. Maybe I'm forgetting something there. Maybe later I'll be back with a new problem. Thanks for all the help, AS.
earth_angel is offline

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