Programming

I am trying to receive a packet of data as bytes in C, but the picture is getting messed up.

I am using fwrite to append bytes to jpg file, but the append or write does not
seem to be appending jpg correctly.

Packet 1 data comes in append to file
Packet 2 data comes in append to file
...
N packets

Code:

void BWrite(unsigned char *b){
    FILE *fp;
    fp = fopen(filename, "ab");
    fwrite(b,1,1,fp);
    fclose(fp);
}

The computer runs centos on flash hard drive.

My brain is fried and out of ideas on how to get this JPEG looking right instead of as bad looking jigsaw puzzle

You're not using the file I/O buffering that fopen gives you, so you may as well use open, which will be quicker...try:

Code:

void BWrite(unsigned char *b){
    int fd;
    fd=open(filename,O_CREAT|O_APPEND,0700);
    write(fd,b,1);
    close(fd);
}

Thanks for reply.

OK, that created the file, but left file empty with 0 bytes.

Any other ideas, my brain hurts.

Also, JPEG is Big-Endian and my CentOS is Little-Endian, so I was trying to
see if reversing the char would correct, but have been unsuccessful so far.
Not sure if this is correct path to fix problem or if writing to disk is problem.

Open to any suggestions, thanks.

---------- Post updated at 11:09 AM ---------- Previous update was at 10:49 AM ----------

Changing your code to:

Code:

void BWrite(unsigned char *b){
    FILE *fd;
    fd=fopen(filename,"ab+");
    write(fd,b,1);
    fclose(fd);
}

wrote to file, but it is not opening as jpg file still???

You can't mix fopen and write() calls. fopen belongs with fwrite, open belongs with write.

Your first code wasn't wrong, either. It looks like it should write one more byte onto the end of the file.

I think what's wrong is the fact that you're writing single bytes. Are you sure your packets are single bytes? That seems really odd! You might be throwing out 99% of the packet.

I am getting all the data as bytes in packets.

What ways are there to wright data blocks of bytes?

Maybe 10 bytes a block.

Would this affect the JPEG image size, because all jpg files
have the same size, even when camera sends different size
images.

Of course you are. Anything chunk of data whatsoever can be represented as 8-bit bytes. But that doesn't mean you're getting only one byte! You already know 2 different ways. The difference is that, instead of using them to write 1 byte, you use them to write more. Do you actually know that? Do you know your packets are even all the same size? You shouldn't have to guess -- something, somewhere in your code must know the size of the packet you received, but you're either not keeping that result or not using it...

Unfortunately we can't see your code from here. Please post it.

I certainly hope it would affect the jpeg image size, right now they're only going to be a tiny fraction of the size they should be.

I don't have documentation that is the problem and I am forced to try and understand how to get this JPEG image correct.

Documentation does say image size is

Code:

0xNNMMZZYY - Image Size 32 bits

The data for example gives me:
NN=0
MM=0
ZZ=10
YY=64

I know how many data bytes total from the formula I calulated.
((zz - 1) * 259) + 256 + YY = DataSize for individual packets

Don't know what the formula means, but it works, so I tried to append
the bytes one by one, but got a fuzzy image and I know the camera works
because the older pascal code works and uses a Blockwrite function:

Code:

 Blockwrite(MyFileHandle, byte, 1, BytesRead);

which writes byte by byte in a loop, similar to the way I first explained and tried to emulate.