C, howto read binary file into buffer

carbonfiber · 01-14-2010, 08:36 AM

Code:

dump_buffer(&buffer, fileLen);

Sergei Steshenko · 01-14-2010, 09:00 AM

Quote:

Originally Posted by carbonfiber

Code:

dump_buffer(&buffer, fileLen);

Yep, it's a mistake, but, still, in the very first post:

Quote:

Could somebody provide a complete example of code that shows how to read a binary file into a buffer/array in C

.

I.e. even a correct WRT the above mistake program won't print much meaningful data because of

Code:

printf("%c", ((char *)buffer)[i]);

.

theNbomr · 01-14-2010, 09:59 AM

If all you want to do is see the content of a binary file in a 'readable' format, then od is a useful tool.
--- rod.

carbonfiber · 01-14-2010, 10:44 AM

Sergei Steshenko: I know. I wasn't disagreeing with your post, I was simply pointing out one mistake I thought would tourment him later on.

naphstor · 01-14-2010, 10:57 PM

Quote:

Originally Posted by Sergei Steshenko

What kind of data do you expect on the screen and why do you expect it to look not like junk ? I.e. do you know what data is displayed on screen as something meaningful and what data as junk/gibberish ? If I may, have you ever heard of ASCII ? If not, try to perform web search on ASCII and/or try

man ascii

on your UNIX/Linux bix.

hi i m sorry, if had done any mistake. i actually meant to say that my output screen shows output in ascii data, then it holds for some seconds and prints something weird, which doesnt look like ascii. and then in the last it stops by saying segmentation fault.
so coz of that i said i am getting some junk data. the output i got is shown below.

Quote:

[root@is02vmbig code]# ./test4.out
value isð2ÀH,ü¿3n ð2ÀH,ü¿3nt,ü¿|,ü¿FKôo¨,ü¿H,ü¿ð+ü¿õmÔï
JÐSÔï
½
D t,ü¿ÐSl,ü¿¿0¿<¿Z¿e¿u¿¿ª¿½¿Ç¿þ¿¤þ¿*þ¿Âþ¿æþ¿÷þ¿*þ¿2þ¿=þ¿Jþ¿þ¿«þ¿Àþ¿Îþ¿ÿóëd
[-ü¿i686PuTTY./test4.outHOSTNAME=is02vmbig.ittiam.comTERM=xtermSHELL=/bin/bashHISTSIZE=1000SSH_CLIENT=::ffff:172.20.33.23 4410 22SSH_TTY=/dev/pts/1USER=rootLS_COLORS=no=00:fi=00:di=00;34:ln=00;36i=40;33:so=00;35:bd=40;33;01:cd=40;33;01r=01;05 ;37;41:mi=01;05;37;41:ex=00;32:*.cmd=00;32:*.exe=00;32:*.com=00;32:*.btm=00;32:*.bat=00;32:*.sh=00;3 2:*.csh=00;32:*.tar=00;31:*.tgz=00;31:*.arj=00;31:*.taz=00;31:*.lzh=00;31:*.zip=00;31:*.z=00;31:*.Z= 00;31:*.gz=00;31:*.bz2=00;31:*.bz=00;31:*.tz=00;31:*.rpm=00;31:*.cpio=00;31:*.jpg=00;35:*.gif=00;35: *.bmp=00;35:*.xbm=00;35:*.xpm=00;35:*.png=00;35:*.tif=00;35:MAIL=/var/spool/mail/rootPATH=/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin:/root/mv_pro_4.0/montavista/pro/devkit/arm/v5t_le/bin:/root/mv_pro_4.0/montavista/pro/devkit/arm/v5t_le/armv5tl-montavista-linuxeabi/binINPUTRC=/etc/inputrcPWD=/win_d/WORKS/NEW_TOOL/TEST/codeLANG=en_US.UTF-8SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpassSHLVL=1HOME=/rootLOGNAME=rootSSH_CONNECTION=::ffff:172.20.33.23 4410 ::ffff:172.20.33.44 22LESSOPEN=|/usr/bin/lesspipe.sh %sG_BROKEN_FILENAMES=1_=./test4.outOLDPWD=/win_d/WORKS/NEW_TOOL/TEST./test4.outSegmentation fault

now i cant make out why is it showing this kind of output.
thanks.

naphstor · 01-14-2010, 11:55 PM

my actual requirement is that, i have a bitstream of some 100mb. now i want to extract some 1000 bytes from it. well i dont know exactly how to perform this action so i tried to fread the file. but i still dont know how to extract some fixed number of data from binary file and display it in bits format.

would appreciate any reply.

Sergei Steshenko · 01-15-2010, 04:05 AM

Quote:

Originally Posted by naphstor

hi i m sorry, if had done any mistake. i actually meant to say that my output screen shows output in ascii data, then it holds for some seconds and prints something weird, which doesnt look like ascii. and then in the last it stops by saying segmentation fault.
so coz of that i said i am getting some junk data. the output i got is shown below.

now i cant make out why is it showing this kind of output.
thanks.

As I have already asked, why do you expect a different output ? I.e. justify your expectations first.

Sergei Steshenko · 01-15-2010, 04:06 AM

Quote:

Originally Posted by naphstor

my actual requirement is that, i have a bitstream of some 100mb. now i want to extract some 1000 bytes from it. well i dont know exactly how to perform this action so i tried to fread the file. but i still dont know how to extract some fixed number of data from binary file and display it in bits format.

would appreciate any reply.

Try

man split

first.

Corsari · 11-27-2014, 05:02 PM

Do any of you have any clue of how to apply this to read RAW disk content?

I'm doing some learning stage of ANSI C under linux and in my first attempt

I'd like

- read raw sectors form e.g /dev/sdb
- sequentially get one sector (so its 512 bytes) at a time
- print on the terminal the 512 bytes as ASCII characters (not formatted, just a raw output, ok, also formatted but it is not a must)
- at next sector, overwrite the precedent 512 characters (terminal should not scroll up)
- loop so fast until a user break happen

Thank you for helps
Cor

theNbomr · 11-27-2014, 05:32 PM

The majority of the question from the original poster (and you should have started your own thread, not hijack an existing and quite old one) has to do with the representation of his binary data. The problem is that ASCII doesn't define all 256 bytes as characters, and many of the one that it does define are not printable as human-readable glyphs.
Having said that, I suggest NOT reading partitions or block devices as a learning exercise. Read/write files, instead. When you print the contents, format it in human readable form, such as hex or octal text, with lines that break on friendly byte boundaries, etc. Example (untested)

Code:

for( i = 0; i < sizeof( myBuffer ); i++ ){
    if( i % 16 == 0 ){
        printf( "\n%08X: ", i );
    }
    printf( "%02X ", myBuffer[i] );
}