I got the problem with my program made for downloading the DateTimeOrginal data from the .JPG file. I found the document about it on the internet:
https://ExifTool.org/TagNames/EXIF.html
I see that the data I'm looking for is at 0x9003 address.
So right now what I'm trying to do is:
temp = fopen(name, "rb");
open the file binary
fseek (temp, 0x9003, SEEK_SET);
move the File pointer to the address
fscanf(temp, "%s", str);
and load the data to the char[] structure.
Is atleast any of that correct? I'm still thinking that i got the problem with the address, because after compile that program i see only some trash from the file.
The EXIF data is embedded into the jpeg tag APP1 (0xE1).
The first thing to do is to find the jpef tag 0xE1 in the stream; you have to scan all the jpeg tags (marked by 0xFF+tag, in your case 0xFF,0xE1). After you get the tag, find its length by reading the next 2 bytes (and adjust for high endian), then get the tag's content.
After you get the tag's content, then look in it for the EXIF tag you are interested in (0x9003).
The method readStream in the jpeg class of the open source project Imebra gives you an example on how to parse jpeg tags: https://bitbucket.org/binarno/imebra/src/2eb33b2170e76b5ad2737d1c2d81c1dcaccd19e5/project_files/library/imebra/src/jpegCodec.cpp?at=default#cl-867
Given the style of programming of the OP, I'd recommend Easyexif at https://github.com/mayanklahiri/easyexif
It's relatively easy to integrate. Note that fseek() goes to a file position; it does not search for a certain number.
Related
My question almost exactly the same as this one which is unanswered. I am trying to read the binary data of a .jpg to send as an HTTP response on a simple web server using C++. The code for reading the data is below.
FILE *f = fopen(file.c_str(),"rb");
if(f){
fseek(f,0,SEEK_END);
int length = ftell(f);
fseek(f,0,SEEK_SET);
char* buffer = (char*)malloc(length+1);
if(buffer){
int b = fread(buffer,1,length,f);
std::cout << "bytes read: " << b << std::endl;
}
fclose(f);
buffer[length] = '\0';
return buffer;
}
return NULL;
When the request for the image is made and this code runs, fread() returns 25253 bytes being read, which seems correct. However, when I perform strlen(buffer) I get only 4. Of course, this gives an error on a browser when the image tries to display. I have also tried manually setting the HTTP content length to 25253 but I then a receive a curl error 18, indicating the transfer ended early (as only 4 bytes exist).
As the other poster mentioned in their question, the 5th byte of the image (and I assume most .jpg images) is 0x00, but I am unsure if this has an effect on saving to the buffer.
I have verified the .jpg images I am loading are in the directory, valid, and display properly when opened normally. I have also tried 2 different methods of loading the binary data, and both also give only 4 bytes, so I am really at a loss. Any help is much appreciated.
When the request for the image is made and this code runs, fread()
returns 25253 bytes being read, which seems correct. However, when I
perform strlen(buffer) I get only 4.
Well there is your problem: You read binary data, not text, meaning that special characters like newline or the null character is not a something that indicates the structure of a text, its simple numbers.
strlen is a function to give you the count of characters other than '\0' or simply 0. However in a binary file like jpeg there a dozen of zeros usually in there, and because of a binary header structure, there seems to be always a zero at position 5 so, so strlen will stop at the first it found and return 4.
Also you seem confused by the fact that you try to send this "text interpreted" jpeg to a HTTP server. Of course it will complain, because you can not simply send binary data as text in HTTP, you either have to encode it, base64 is very popular, or set the content length header. Of course you also have to tell the HTTP client/server the type by setting the proper MIME header.
I'm trying to read struct data from specific position in a a binary file.
Found out that I can use import std.stdio and its File, however all i seem to find is all about string handling.
I have c-code written data on binary files that compose of several different structs and they all, as far as I understand coding lay in a oneliner. In order to find specific struct I need to, like in old c,
Open file for reading .... (binary read??)
using sizeof and move to startposition of struct data to read
read data (struct.sizeof data) into receivingbuffer and
Close file
Documentation for std.stdio.File # read talks about reading entire or up to size but can't find how to read as below c-code line?
fseek(filehandle, sizeof(firstStructData), SEEK_SET));
read(filehandle, (char *)nextReceivingBuffer, sizeof(nextReceivingBuffer))
Any ideas or hints?
Try File.seek and File.rawRead. They work like their C counterparts, but rawRead determines the read count from the size of the output buffer you hand it.
How can i read content of a file which is not a simple text file in c/c++? For example, I want to read image file such as .jpg/.png/.bmp and see the value at certain index,to check what colour it is? or if I have a .exe/.rar/.zip and want to know what value is stored at different indices?
I am aware of c style reading file, which is
FILE *fp;
fp = fopen("example.txt","r"); /* open for reading */
char c;
c = getc(fp) ;
I want to know if i replace "example.txt" with "image.png" or so, will it works? will i get correct data?
When you open a non-text file, you'll want to specify binary (untranslated) mode:
FILE *fp = fopen("example.png", "rb");
In a typical case, you do most of your reading from binary files by defining structs that mirror the structures in the file, and then using fread to read from the file into the structure (but this has to be done carefully, to ensure that things like padding in the struct don't differ between the representation in-memory and on-disk).
You would need to open the file in binary mode. This allows you to read the bytes in a "raw" mode where they are unchanged from what was in the file.
However, determining the color of a particular pixel, etc. requires that you fully understand the meaning of the bytes in the file and how they are arranged for the file being read. This second requirement is much more difficult. You'll need to do some research on the format of that file type in order to do that.
yea ofcorse you can open any file in binary mode in c. if you are interested then you can also read some 1st byte of any such non text file.
In most of the cases all different file-format has some fixed header so based on that you can identify the type of that file.
Open any matroska(.mkv) file and read 1st 4 byte you will always have this
0x1A 0x45 0xDF 0xA3
you can also see any file in binary representation hexdump utility in linux
====================
Edit:
such as .jpg/.png/.bmp and see the value at certain index,to
check what colour it is?
here you need to understand the format of that file and based on that you can know on which place's data what information is indicating..!!!
I am writing a class that compresses binary data using a zlib stream. I have a buffer that I fill with the output stream and once it becomes full I dump the buffer out to a file using fopen(filename, 'ab');... What this means is that my program only opens up the file to write to it whenever it has a buffer full of data to dump, it goes and does it and immediately closes it.
The issue is in my format I use an 8 byte header at the beginning of each file which contains the original length and compressed length but I do not know these values until the end of the whole compression process.
What I wanted to do was write 8 bytes of zeros, then append with all my compressed data, then come back at the end during cleanup to fill in those 8 bytes with the size data, but I can't seem to find a way to open the file without bringing it all back into memory. I just want to edit the first 8 bytes of the file. Do I need to use mmap?
Since you're using the file in append mode, you do need to close and re-open it:
open with fopen(filename, "r+b");
write the 8 bytes;
close the file using fclose().
The r+ means
Open for reading and writing. The stream is positioned at the
beginning of the file.
and the b is needed to open in binary mode.
You can use this method to change the data at any position in the file, not just at the beginning: simply use fseek() to seek to the required position before writing.
Use rewind() to take the file pointer back to the start of the file after you write out the last few bytes of data. You can then output your 8 bytes of length info.
If you have flexibility in changing your format, I might suggest this. Define your compressed stream such that it is a sequence of an unknown number of blocks, and each block is preceded by a fixed length integer specifying the number of bytes in the block. The stream is finished when the next block has a size of zero.
The drawback to this format is that there no way for the reader of the stream to know how much data is coming until it's all been read. But the advantage is that it avoids this problem you are trying to solve.
More importantly, it allows you to send a compressed stream of data somewhere as you read the input and you don't have to save it all before sending it. For example, you could write a compression Unix filter that you could put in a pipe stream:
prog1 | yourprog -compress | rsh host yourprog -expand | prog2
Good luck.
I am trying to read a bmp file in C++(Turbo). But i m not able to print binary stream.
I want to encode txt file into it and decrypt it.
How can i do this. I read that bmp file header is of 54 byte. But how and where should i append txt file in bmp file. ?
I know only Turbo C++, so it would be helpfull for me if u provide solution or suggestion related to topic for the same.
int main()
{
ifstream fr; //reads
ofstream fw; // wrrites to file
char c;
int random;
clrscr();
char file[2][100]={"s.bmp","s.txt"};
fr.open(file[0],ios::binary);//file name, mode of open, here input mode i.e. read only
if(!fr)
cout<<"File can not be opened.";
fw.open(file[1],ios::app);//file will be appended
if(!fw)
cout<<"File can not be opened";
while(!fr)
cout<<fr.get(); // error should be here. but not able to find out what error is it
fr.close();
fw.close();
getch();
}
This code is running fine when i pass txt file in binary mode
EDIT :
while(!fr)
cout<<fr.get();
I am not able to see binary data in console
this was working fine for text when i was passing character parameter in fr.get(c)
I think you question is allready answered:
Print an int in binary representation using C
convert your char to an int and you are done (at least for the output part)
With steganography, what little I know about it, you're not "appending" text. You're making subtle changes to the pixels (shading, etc..) to hide something that's not visually obvious, but should be able to be reverse-decrypted by examining the pixels. Should not have anything to do with the header.
So anyway, the point of my otherwise non-helpful answer is to encourage you go to and learn about the topic which you seek answers, so that you can design your solution, and THEN come and ask for specifics about implementation.
You need to modify the bit pattern, not append any text to the file.
One simple example :
Read the Bitmap Content (after header), and sacrifice a bit from each of the byte to hold your content
If on Windows, recode to use CreateFile and see what the real error is. If on Linux, ditto for open(2). Once you have debugged the problem you can probably shift back to iostreams.