473,324 Members | 2,548 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,324 software developers and data experts.

ifstream and binary file reading problem....

Hello,
Please look the code below where I am reading the first 2,2,4 bytes
from a binary file using two methods.

I am getting a wierd (wrong) output with ifstream and memcpy method,
but get the correct output with CFile read.
I am trying to get the values 1400 1050 and 2014 from the binary file.

Can anybody point out the mistake in the following code?

int main ()
{
ifstream myStream;
filedesc fd;
char sz2[30];
short i = 0;
short j = 0;

//Start Method one
fd = _open("my_binary_file.inf", _O_RDONLY, _O_BINARY);
myStream.clear();
myStream.attach(fd);

myStream.read(sz2, 20);
memcpy( &i, &sz2[0], 2 );
printf("x value is %d \n", i);
memcpy( &i, &sz2[2], 2 );
printf("y value is is %d \n", i);
memcpy( &i, &sz2[4], 4 );
printf("Version is %d \n", i);

myStream.close();
myStream.clear(); // reset eof state

//End Method one

//Start Method two

CFile file("my_binary_file.inf", CFile::modeRead);

file.Read((LPSTR)&j, 2);
printf("x value is %d \n", j);
file.Read((LPSTR)&j, 2);
printf("y value is %d \n", j);
file.Read((LPSTR)&j, 4);
printf("Version is %d \n", j);

file.Close();

//End Method two
return 0;

}

Jul 23 '05 #1
3 4068
sredd01 wrote:
Please look the code below where I am reading the first 2,2,4 bytes
from a binary file using two methods.
Both methods are non-standard. You should consider posting to a newsgroup
dedicated to your platform, since those are probably platform-specific, or
to a newsgroup for your compiler in case they are compiler-specific.
I am getting a wierd (wrong) output with ifstream and memcpy method,
Perhaps you shouldn't use memcpy...
but get the correct output with CFile read.
I am trying to get the values 1400 1050 and 2014 from the binary file.

Can anybody point out the mistake in the following code?

int main ()
{
ifstream myStream;
filedesc fd;
char sz2[30];
short i = 0;
short j = 0;

//Start Method one
fd = _open("my_binary_file.inf", _O_RDONLY, _O_BINARY);
myStream.clear();
myStream.attach(fd);
I am unaware of any 'attach' members in 'ifstream'. Why don't you simply
open the stream instead of this?

myStream.open("my_binary_file.inf", ios::binary);
myStream.read(sz2, 20);
memcpy( &i, &sz2[0], 2 );
printf("x value is %d \n", i);
memcpy( &i, &sz2[2], 2 );
printf("y value is is %d \n", i);
memcpy( &i, &sz2[4], 4 );
printf("Version is %d \n", i);
This is rather strange. Why don't you simply read the fields are they are
intended (and in order to compare to the CFile method):

myStream.read(reinterpret_cast<char*>(&i), sizeof(short));

???

myStream.close();
myStream.clear(); // reset eof state

//End Method one

//Start Method two

CFile file("my_binary_file.inf", CFile::modeRead);

file.Read((LPSTR)&j, 2);
printf("x value is %d \n", j);
file.Read((LPSTR)&j, 2);
printf("y value is %d \n", j);
file.Read((LPSTR)&j, 4);
printf("Version is %d \n", j);

file.Close();

//End Method two
return 0;

}


V
Jul 23 '05 #2
REH

"sredd01" <rs*****@gmail.com> wrote in message
news:11**********************@g14g2000cwa.googlegr oups.com...
myStream.read(sz2, 20);
memcpy( &i, &sz2[0], 2 );
printf("x value is %d \n", i);
memcpy( &i, &sz2[2], 2 );
printf("y value is is %d \n", i);
memcpy( &i, &sz2[4], 4 );
printf("Version is %d \n", i);

This is implementation-specific. The size of i and j are as least 2, but
may not be big enough to hold four bytes.
Jul 23 '05 #3
Thanks a lot for your help.
I figured it out.

Jul 23 '05 #4

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

1
by: wtnt | last post by:
Hello. I've searched all over and haven't seen another thread with this problem. Please bear with me as I try to explain. thanks. :) I have some programs that need to be cross-platform...
4
by: Dr. Len | last post by:
Hi all! Given that I have a binary file which contains 4-byte integer values in sequence and I know in advance how many there are, does the C++ standard have any algorithm or like method to read...
5
by: Jacek Dziedzic | last post by:
Hi! Consider the following program #include <fstream> #include <iostream> using namespace std; int main() { ifstream in("test.txt");
7
by: shawn | last post by:
Hi All, Am using MSVC6 compiler on a WinXP machine. Am trying to read a file using std::ofstream; the problem is that Tofstream.is_open() fails and Tifstream.rdstate() returns "2" which...
7
by: Hamburgpear | last post by:
Dear All, Is it possible to reset the value of xxx.peek() after it reachs EOF ? Regards HP
3
by: farseer | last post by:
Hi, Hi, i am reading the content of a binary file, enoding as base64 and writing to an output file. After noticing that my output file seems to be truncated, i created the following simple test...
3
by: toton | last post by:
Hi, I want to unread a few things while I am reading a file. One solution I know is putback the characters read to the buffer. But as I need frequent moving file pointer , to a few steps back, I...
1
by: SantaClaus | last post by:
Hi all, Im getting an exception in the middle of reading a file and here is my code std::ifstream inf; const int bufSize=1024; char tbuffer; std::string filex = path; // may be C:\test.txt const...
0
by: James Kanze | last post by:
On 11 avr, 17:44, "mc" <mc_r...@yahoo.comwrote: OK. If the actual format is well documented, that's half the battle won already. Note, however, that reading a float as an int is still very...
0
by: DolphinDB | last post by:
Tired of spending countless mintues downsampling your data? Look no further! In this article, you’ll learn how to efficiently downsample 6.48 billion high-frequency records to 61 million...
0
by: ryjfgjl | last post by:
ExcelToDatabase: batch import excel into database automatically...
0
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
1
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
1
by: PapaRatzi | last post by:
Hello, I am teaching myself MS Access forms design and Visual Basic. I've created a table to capture a list of Top 30 singles and forms to capture new entries. The final step is a form (unbound)...
1
by: Defcon1945 | last post by:
I'm trying to learn Python using Pycharm but import shutil doesn't work
1
by: Shællîpôpï 09 | last post by:
If u are using a keypad phone, how do u turn on JavaScript, to access features like WhatsApp, Facebook, Instagram....
0
by: af34tf | last post by:
Hi Guys, I have a domain whose name is BytesLimited.com, and I want to sell it. Does anyone know about platforms that allow me to list my domain in auction for free. Thank you
0
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 3 Apr 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome former...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.