I am looking for a way to extract the data from the 'Root Directory'.
This is using a FAT 12 floppy image. This is with Ubuntu Version 14.04.2.
I would like to be able to read the root entries found in the root sector (from what I understand this is sector 19 - 32), I would then like to be able to display the content stored in the entries (file names, directory names). This needs to be for system level programming.
traverse(){
unsinged char buf[1000];
int fd = open("CDBOOT1.IMG", O_RDONLY);
lseek(fd, 19 * 512, SEEK_SET);
read(fd, buf, 512);
}
I would like some information on how I can parse out the information in the buf array to get the information I desire. This is for a homework assignment, so I am not looking for a concrete answer, but maybe some resources on how to do this.
Update:
From advice, I used some of the other code (already written by someone else) so that it would print the HEX data of the sector I am trying to get the root data from (I can post the code for that if it is necessary). With the HEX table, I am still unsure how to interpret the data in order to get the file information, directory information, date created, etc.
I've done some parsing of FAT in the past. It can be tricky if you're not used to it.
One thing I'd strongly recommend is doing a hex dump of what you read in C and, save it in in a file and then bring it up in a good hex editor so you can verify that your algorithms are right and things are laid out as you expect. That everything cross-checks which what you get from the spec.
Here is a spec:
http://www.maverick-os.dk/FileSystemFormats/FAT12_FileSystem.html
You are really looking for two things here. The FAT contains data the represents clusters and fragments of clusters. But you also want to read the DET ( Directory Entry Table ) to get names and things like that.
So what you REALLY need to do is start here:
http://en.wikipedia.org/wiki/File_Allocation_Table
and read up on how these things are designed. This is neither simple or trivial code, even with an image file. The image file may even have things embedded in it for the software that reads and writes it.
Related
I have a file that holds manufacturing orders for a machine.
I would like to read the content of this file and edit it, but when I open it in a text editor i.e. Notepad++, I get a bunch of wierd charecters:
xÚ¥—_HSQÀo«a)’êaAXŽâê×pD8R‰¬©s“i+ƒ´#¡$
-þl-ó/ÓíºIúPôàƒHˆP–%a&RÎÈn÷ü¹·;Ú;ç<ìòÝÃý}¿ó}‡{϶«rWg>˜›ãR‡)Çn0³Ûf³yÎW[5–šw½ÇRW{ñ’rO6¹ŽŸp¦ÙœcÏ.9yÀnýg
)Ë—e90ejÕø£rC. f¦}3ËŒ˜hü”å1g[…ø±ú ÜJøz®‹˜YfÈ,4`ŽKÉ—ù“ÔË¿d„þlG3#=˜Ž´+hF¬¦£€«šm¿áØ
ïÖµv‡ËpíÍ~™‡Aù
šëÈÚ]ÿç™DŒÉFØ ïƒæsij ¦y=-74Æ/t=ÕŠr\˜š»Âä‰Ý¨žã΢
dz·à‡'fœ½yâ½4qåPjácòÄŒeÊhñ“ý™ÙÎÕ÷5ôlñ=˜Õ{ú;ø=Û;4OêYä>Ìpxbæâ'è"oëB×1gQ9“'¹]Ô³’Ô³ø!ÌózÞyŸõžÓIŽù*&OÌXPÕ"ŽWžpíOÌè‚Þ3Òr0{Ž†R=_?…/¼žÞ0,ê=/?£ûÓËîy“2Z<ij³[ËÁì™÷–ôžÎ’Ããa÷<Maêéí…¼ž}©žYýZ-˜=”á¤}π＞3°¢÷œ$ïè‰3ìž«ƒÄs¿—xnŒÀ*¯gi$ÕómDËÁìùIeоû‡À¬?3°x¾"~ª§c˜öÝÇî颌°›x¾Fßb>Ï}QXÓ{öFi-êÙßóR”œe^Ñ÷ü‘¿g[Lë ŽwJZϘë¹3”³L©gH‚,^Ïe 2ôžWGøëÙ2‚Î
øœL¾ÅqÈäõ,ýç\œË3¾þeྗ&`Ϻ<KÒf“’»ðù]í‰ãžU^wèþåÔÖy”H}ò•6ø6
It looks like the file is encoded.
Any idea how to find the encoding and make the file readable and editable?
It's binary and probably encoded so without knowledge of data structure you can't do much - just reverse engineering based on trying and checking what changed, operating with hex editor.
It isn't impossible, tho. If you can change the data the way you know (eg. change number of orders from 1 to 2) and export to file, you can compare binary values and find which byte holds that number. Of course if it is encrypted and you don't know the key... It's easier to find another way.
For further read, check this out - https://en.wikibooks.org/wiki/Reverse_Engineering/File_Formats
If you've got access to a Linux box why not use
hexdump -C <filename>
You will be able to get a much better insight into how the file is structured, than by using a text editor.
There are also many "hexdump" equivalent commands on Windows
I come to you completely stumped. I do some side work for a company that uses an old DOS based program to input and retrieve data. This is a legacy piece of software, and they have since moved to either QuickBooks or Outlook for all of their address or billing related needs. However there have been some changes made, and they work with this database fairly regularly. Since the computer that this software is on, is running XP (and none of the other computers in the office can run it) they're looking to phase this software out for when the computer inevitably explodes.
TLDR; I have an old .csv file (roughly two years) that has a good chunk of information on it, but again it's two years old. I have another file called ml.dat (I'm assuming masterlist.dat) that's in the same folder as this legacy software. I open it with notepad and excel and am presented with information like this:
S;Û).;PÃS;*p(â'a,µ,
The above chunk of text is recognized much less within notepad or excel. It's a lot more of the unrecognized squares.
Some of the information is actually readable however. I can for example read the occasional town name, or person's name but I'm unable to get all of the information since there's a lot missing. Perhaps the data isn't in unicode or something? I have no idea. Any suggestions? I'm ultimately trying to take this information and toss it into either quickbooks or outlook.
Please help!
Thanks
Edit: I'm guessing the file might be encrypted since .dat's are usually clear text? Any thoughts?
.DAT files can be anything, they are usually just application data. Since there is readable text, then it is very unlikely that this file is encrypted. Instead you are seeing ASCII representations of the bytes of other content. http://www.asciitable.com/ Assuming single byte values, the number 77 might appear in the file somewhere as M.
Your options:
Search for some utility to load and translate the dat file for that application.
Set up an appropriate dos emulator so you can run this application on another box, or even a virtual machine running freedos or something.
Figure out the file format and then write a program to translate the data.
For #3, you can attach a debugger to the application to trace how the file is read and written. Alternatively you can try to figure out record boundaries (if all the records are the same size, then things are a little bit easier.) Then you can use known values to try to find field boundaries. If you can find (or reverse compile) the source code, then that could also give you insight into the file format.
1 is your best bet, and #2 will buy you some time so that you don't need that original machine anymore. #3 would likely be something to outsource.
If you can find the source or file format, then you just recreate whatever data structure was dumped to the file and read the file into it.
To find which exe opens it, you can do something like:
for %f in (*.exe) do find "ml.dat" %f -c
Assuming the original application was written in C then there would be code something like this to read the first record from the file:
struct SecretData
{
int first;
double money;
char city[10];
};
FILE* input;
struct SecretData secretdata;
input = fopen("ml.dat", "rb");
fread(&data, sizeof(data), 1, input);
fclose(input);
(The file would have been written with fwrite.) Basically you need to figure out the innards of the SecretData structure to be able to read the file.
There likely wasn't a separate utility used to make the file, dumping data and reading it back from a file is relatively easy in most languages.
I have a program which logs its activity.
I want to implement a log file mechanism to keep the log file under a certain size, lets say 10 MB.
The log file itself just holds commands the program executed; those commands are variable length.
Right now, the program runs on a windows environment, but I'm likely to port it to UNIX soon.
I've came up with two methods for managing the log files:
1. Keep multiple files of lower size, and if the new command exceeds the current file length, truncate the oldest file to zero size, and start writing there.
2. Keep a header in the file, which holds metadata regarding the first command in the file, and the next place to write to in the file. Also I think, each command should hold metadata about it's length this way.
My questions are as follows:
In terms of efficiency which of these methods would you use, and why?
Is there a unix command / function to this easily?
Thanks a lot for your help,
Nihil.
On UNIX/Linux platforms there's a logrotate program that manages logfiles. Details can be found for example here:
http://linuxcommand.org/man_pages/logrotate8.html
i would like to know how could I possibly use the programming language C to create a file archiver such as tar.
Im stuck on the first bit on how to copy a bunch of files into one file, and then extrating them back out of that one file.
Any help would be appreciated thanks.
It's a good idea to read up on the tar format for some inspiration.
http://en.wikipedia.org/wiki/Tar_%28file_format%29
http://www.gnu.org/software/automake/manual/tar/Standard.html
It's quite simple and shouldn't be too hard to implement yourself, if you got a good grasp of basic C I/O.
Assuming you don't want compression, which is pretty hard, and just want's something REALLY simple, you are gonna need to do the following:
Create a file to hold all the files you want.
Fetch one of the files you want to archive, get it's name, name_size and it's size.
Write the name_size of the name, name, size of the file, and the size * bytes of the file into the archive one.
Repeat to all of the files you want to archive.
To get the files back from the one archive, you are gonna need to read the name's size, create that file with the next name_size next bytes, then read the size of the file bytes, and write them to the single file you created.
You would have this:
File1:
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
FileN:
yyyyyyyyyyyyyyyyyyyy
After the archiving you would have:
5File1size of File1xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx5FileNsizeof FileNyyyyyyyyyyyyyyyyyyyy
just had a general question about how to approach a certain problem I'm facing. I'm fairly new to C so bear with me here. Say I have a folder with 1000+ text files, the files are not named in any kind of numbered order, but they are alphabetical. For my problem I have files of stock data, each file is named after the company's respective ticker. I want to write a program that will open each file, read the data find the historical low and compare it to the current price and calculate the percent change, and then print it. Searching and calculating are not a problem, the problem is getting the program to go through and open each file. The only way I can see to attack this is to create a text file containing all of the ticker symbols, having the program read that into an array and then run a loop that first opens the first filename in the array, perform the calculations, print the output, close the file, then loop back around moving to the second element (the next ticker symbol) in the array. This would be fairly simple to set up (I think) but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this? Not really asking for code ( unless there is some amazing function in c that will do this for me ;) ), just some advice from more experienced C programmers.
Thanks :)
Edit: This is on Linux, sorry I forgot to metion that!
Under Linux/Unix (BSD, OS X, POSIX, etc.) you can use opendir / readdir to go through the directory structure. No need to generate static files that need to be updated, when the file system has the information you want. If you only want a sub-set of stocks at a given time, then using glob would be quicker, there is also scandir.
I don't know what Win32 (Windows / Platform SDK) functions are called, if you are developing using Visual C++ as your C compiler. Searching MSDN Library should help you.
Assuming you're running on linux...
ls /path/to/text/files > names.txt
is exactly what you want.
opendir(); on linux.
http://linux.die.net/man/3/opendir
Exemple :
http://snippets.dzone.com/posts/show/5734
In pseudo code it would look like this, I cannot define the code as I'm not 100% sure if this is the correct approach...
for each directory entry
scan the filename
extract the ticker name from the filename
open the file
read the data
create a record consisting of the filename, data.....
close the file
add the record to a list/array...
> sort the list/array into alphabetical order based on
the ticker name in the filename...
You could vary it slightly if you wish, scan the filenames in the directory entries and sort them first by building a record with the filenames first, then go back to the start of the list/array and open each one individually reading the data and putting it into the record then....
Hope this helps,
best regards,
Tom.
There are no functions in standard C that have any notion of a "directory". You will need to use some kind of platform-specific function to do this. For some examples, take a look at this post from Cprogrammnig.com.
Personally, I prefer using the opendir()/readdir() approach as shown in the second example. It works natively under Linux and also on Windows if you are using Cygwin.
Approach 1) I would just have a specific directory in which I have ONLY these files containing the ticker data and nothing else. I would then use the C readdir API to list all files in the directory and iterate over each one performing the data processing that you require. Which ticker the file applies to is determined only by the filename.
Pros: Easy to code
Cons: It really depends where the files are stored and where they come from.
Approach 2) Change the file format so the ticker files start with a magic code identifying that this is a ticker file, and a string containing the name. As before use readdir to iterate through all files in the folder and open each file, ensure that the magic number is set and read the ticker name from the file, and process the data as before
Pros: More flexible than before. Filename needn't reflect name of ticker
Cons: Harder to code, file format may be fixed.
but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this?
I have solved the exact same problem a while back, albeit for personal uses :)
What I did was to use the OS shell commands to generate a list of those files and redirected the output to a text file and had my program run through them.
On UNIX, there's the handy glob function:
glob_t results;
memset(&results, 0, sizeof(results));
glob("*.txt", 0, NULL, &results);
for (i = 0; i < results.gl_pathc; i++)
printf("%s\n", results.gl_pathv[i]);
globfree(&results);
On Linux or a related system, you could use the fts library. It's designed for traversing file hierarchies: man fts,
or even something as simple as readdir
If on Windows, you can use their Directory Management API's. More specifically, the FindFirstFile function, used with wildcards, in conjunction with FindNextFile